#import "lib/unify.typ": qty, qtyrange
#import "@preview/cetz:0.5.2"

= Mechanical specifications <mechanical-specifications>

== Modules <modules>

=== Cassette <cassette>

==== Shielding and construction <shielding-and-construction>

To achieve metrologic tier precision, modules must be fully shielded from
external interference. The only entry points for noise are:

- The DB-25 and BNC connectors at the rear, which connects via a shielded cable
  to the power distribution board
- The banana jacks at the front panel, which include input protection circuits.

Modules must also not pollute neighboring modules with internally generated
noise (such as PWAM oscillators). For this reason, all modules are enclosed in
individual steel cassettes.

We chose steel instead of aluminum, as it has better shielding properties,
especially in terms of magnetic shielding.

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Material], [DC01 cold-rolled steel (EN 10130)],
    [Thickness], [$qty(1.2, "mm")$],
    [Finish], [Matte black powder coard (RAL 9005), all surfaces.],
  ),
  caption: [Cassette construction parameters],
) <table-cassette-construction-parameters>

==== External dimensions <cassette-external-dimensions>

#figure(
  cetz.canvas({
    import cetz.draw: *

    // Scale factor: 1 mm = 0.06 drawing units
    let s = 0.06

    let h-panel = 177.8 * s // 6.223
    let h-body = 165.1 * s // 5.7785
    let h-lip = 6.35 * s // 0.22225
    let w-panel = 38.0 * s // 1.33
    let d-body = 152.4 * s // 5.334
    let t-panel = 3.0 * s // 0.105 (exaggerated slightly for visual clarity)

    let y-center = 0
    let y-top-panel = h-panel / 2
    let y-bot-panel = -h-panel / 2
    let y-top-body = h-body / 2
    let y-bot-body = -h-body / 2

    // --- FRONT ELEVATION ---
    let x-front-left = 0
    let x-front-right = w-panel
    let x-front-mid = w-panel / 2

    // View Title
    content((x-front-mid, y-top-panel + 0.8), text(
      size: 9pt,
      weight: "bold",
    )[FRONT ELEVATION])

    // Front Panel Outline
    rect(
      (x-front-left, y-bot-panel),
      (x-front-right, y-top-panel),
      fill: luma(250),
      stroke: 1.2pt + black,
    )

    // Hidden Body Transition Lines (Dashed)
    line(
      (x-front-left, y-top-body),
      (x-front-right, y-top-body),
      stroke: (paint: luma(130), thickness: 0.7pt, dash: "dashed"),
    )
    line(
      (x-front-left, y-bot-body),
      (x-front-right, y-bot-body),
      stroke: (paint: luma(130), thickness: 0.7pt, dash: "dashed"),
    )

    // Panel Mounting Screw Holes (Top and Bottom Lips)
    circle(
      (x-front-mid, y-top-panel - h-lip / 2),
      radius: 0.08,
      fill: white,
      stroke: 0.8pt + black,
    )
    circle(
      (x-front-mid, y-bot-panel + h-lip / 2),
      radius: 0.08,
      fill: white,
      stroke: 0.8pt + black,
    )

    // Dimension: Panel Width (38.0 mm)
    line(
      (x-front-left, y-bot-panel),
      (x-front-left, y-bot-panel - 0.6),
      stroke: 0.5pt + luma(120),
    )
    line(
      (x-front-right, y-bot-panel),
      (x-front-right, y-bot-panel - 0.6),
      stroke: 0.5pt + luma(120),
    )
    line(
      (x-front-left, y-bot-panel - 0.6),
      (x-front-right, y-bot-panel - 0.6),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.12,
      stroke: 0.7pt + black,
    )
    content((x-front-mid, y-bot-panel - 0.9), text(
      size: 7.5pt,
    )[$qty(38.0, "mm")$])

    // Dimension: Panel Height (177.8 mm / 4U)
    line(
      (x-front-left, y-top-panel),
      (x-front-left - 0.6, y-top-panel),
      stroke: 0.5pt + luma(120),
    )
    line(
      (x-front-left, y-bot-panel),
      (x-front-left - 0.6, y-bot-panel),
      stroke: 0.5pt + luma(120),
    )
    line(
      (x-front-left - 0.6, y-bot-panel),
      (x-front-left - 0.6, y-top-panel),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.12,
      stroke: 0.7pt + black,
    )
    content(
      (x-front-left - 0.95, y-center),
      text(size: 7.5pt)[$qty(177.8, "mm")$ ($qty(4, "U")$)],
      angle: 90deg,
    )

    // --- SIDE ELEVATION ---
    let x-side-start = 2.8
    let x-panel-back = x-side-start + t-panel
    let x-body-rear = x-panel-back + d-body
    let x-side-mid = (x-side-start + x-body-rear) / 2

    // View Title
    content((x-side-mid, y-top-panel + 0.8), text(
      size: 9pt,
      weight: "bold",
    )[SIDE ELEVATION])

    // Cassette Steel Body
    rect(
      (x-panel-back, y-bot-body),
      (x-body-rear, y-top-body),
      fill: luma(235),
      stroke: 1.2pt + black,
    )

    // Front Panel Plate Attached to Body
    rect(
      (x-side-start, y-bot-panel),
      (x-panel-back, y-top-panel),
      fill: luma(210),
      stroke: 1.2pt + black,
    )

    // Rear DB-25 Connector Standoff / Bezel Projection
    rect(
      (x-body-rear, y-center - 0.6),
      (x-body-rear + 0.25, y-center + 0.6),
      fill: luma(240),
      stroke: 0.8pt + black,
    )

    // Dimension: Depth (152.4 mm)
    line(
      (x-panel-back, y-top-panel),
      (x-panel-back, y-top-panel + 0.2),
      stroke: 0.5pt + luma(120),
    )
    line(
      (x-body-rear, y-top-panel - 0.4),
      (x-body-rear, y-top-panel + 0.2),
      stroke: 0.5pt + luma(120),
    )
    line(
      (x-panel-back, y-top-panel + 0.2),
      (x-body-rear, y-top-panel + 0.2),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.12,
      stroke: 0.7pt + black,
    )
    content(((x-panel-back + x-body-rear) / 2, y-top-panel + 0.4), text(
      size: 7.5pt,
    )[$qty(152.4, "mm")$])

    // Dimension: Body Height (165.1 mm)
    line(
      (x-body-rear, y-top-body),
      (x-body-rear + 0.6, y-top-body),
      stroke: 0.5pt + luma(120),
    )
    line(
      (x-body-rear, y-bot-body),
      (x-body-rear + 0.6, y-bot-body),
      stroke: 0.5pt + luma(120),
    )
    line(
      (x-body-rear + 0.6, y-bot-body),
      (x-body-rear + 0.6, y-top-body),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.12,
      stroke: 0.7pt + black,
    )
    content(
      (x-body-rear + 0.9, y-center),
      text(size: 7.5pt)[$qty(165.1, "mm")$],
      angle: -90deg,
    )

    // Dimension: Top Lip Height (6.35 mm)
    line(
      (x-panel-back, y-top-panel),
      (x-body-rear + 1.8, y-top-panel),
      stroke: 0.4pt + luma(160),
    )
    line(
      (x-panel-back, y-top-body),
      (x-body-rear + 1.8, y-top-body),
      stroke: 0.4pt + luma(160),
    )
    line(
      (x-body-rear + 1.65, y-top-body),
      (x-body-rear + 1.65, y-top-panel),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.10,
      stroke: 0.7pt + black,
    )
    content(
      (x-body-rear + 2.2, (y-top-panel + y-top-body) / 2),
      text(size: 7.0pt)[$qty(6.35, "mm")$],
    )
  }),
  caption: [Cassette enclosure orthographic projections (front and side elevation) detailing external physical dimensions and lip offsets.],
) <figure-cassette-external-dimensions-diagram>

#figure(
  table(
    columns: 4,
    table.header([Dimension], [Value], [Tolerance], [Note]),
    [Panel height],
    [$qty(177.8, "mm")$ ($qty(4, "U"), qty(7, "inch")$)],
    [$plus.minus qty(0.1, "mm")$],
    [Full rack unit height],

    [Grid pitch],
    [$qty(38.1, "mm")$ ($qty(1.5, "inch")$)],
    [N/A],
    [Theoretical center to center spacing. Two columns of banana jacks
      ($qty(0.75, "inch")$ grid).],

    [Panel Width],
    [$qty(38.0, "mm")$ ($qty(1.5, "inch")$)],
    [$+0.0 "/" -0.1 "mm"$],
    [Undersized to accomodate paint thickness and thermal expansion.],

    [Body height], [$qty(165.1, "mm")$, ($qty(6.5, "inch")$)], [$plus.minus qty(0.1, "mm")$], [Fits between rails],

    [Body width], [$qty(38.0, "mm")$ ($qty(1.5, "inch")$)], [$+0.0 "/" -0.1 "mm"$], [Same as panel],

    [Depth], [$qty(152.4, "mm")$ ($qty(6, "inch")$)], [$plus.minus qty(0.2, "mm")$], [Front to rear],

    [Lip height], [$qty(6.35, "mm")$ ($qty(0.25, "inch")$)], [N/A], [Top and bottom],
  ),
  caption: [Cassette external dimensions],
) <table-cassette-external-dimensions>

The panel lips extend above and below the cassette body to fill the full
$qty(4, "U")$ rack opening while the body fits between the chassis rails.

==== Construction <cassette-construction>

The cassette consists of the front panel, one L-shaped steel channel and one
interlocking U-shaped steel channel:

===== L-channel (chassis) <l-channel-chassis>

#figure(
  cetz.canvas({
    import cetz.draw: *

    // Scale factor: 1 mm = 0.030 drawing units
    let s = 0.030

    let h = 165.1 * s // 4.953
    let d = 152.4 * s // 4.572
    let w = 35.7 * s // 1.071
    let f = 8.0 * s // 0.240 (8 mm flange width)

    let db25-y = 55.0 * s // 1.650
    let bnc-y = 130.0 * s // 3.900
    let db25-x = 17.85 * s // 0.5355 (centered in 35.7 mm width)

    let y-bot = 0
    let y-top = h

    // ==========================================
    // 1. LEFT ELEVATION (Left Wall: 152.4 x 165.1 mm)
    // ==========================================
    let x-left-start = 0
    let x-left-end = x-left-start + d
    let x-left-mid = (x-left-start + x-left-end) / 2

    // View Title
    content((x-left-mid, y-top + 0.8), text(
      size: 8.5pt,
      weight: "bold",
    )[LEFT ELEVATION])

    // Main Left Wall Sheet
    rect(
      (x-left-start, y-bot),
      (x-left-end, y-top),
      fill: luma(245),
      stroke: 1.2pt + black,
    )

    // Folded Flanges (Top, Bottom, Front folded 90 deg inward - shown as dashed lines)
    // Top Flange
    line(
      (x-left-start, y-top - f),
      (x-left-end, y-top - f),
      stroke: (paint: luma(120), thickness: 0.7pt, dash: "dashed"),
    )
    // Bottom Flange
    line(
      (x-left-start, y-bot + f),
      (x-left-end, y-bot + f),
      stroke: (paint: luma(120), thickness: 0.7pt, dash: "dashed"),
    )
    // Front Flange (at x-left-start)
    line(
      (x-left-start + f, y-bot),
      (x-left-start + f, y-top),
      stroke: (paint: luma(120), thickness: 0.7pt, dash: "dashed"),
    )

    // PEM Nut Press-Fit Inserts on Flanges (Representative circles)
    circle(
      (x-left-start + f / 2, y-bot + 12 * s),
      radius: 0.06,
      fill: white,
      stroke: 0.6pt + black,
    )
    circle(
      (x-left-start + f / 2, y-top - 12 * s),
      radius: 0.06,
      fill: white,
      stroke: 0.6pt + black,
    )
    circle(
      (x-left-mid, y-bot + f / 2),
      radius: 0.06,
      fill: white,
      stroke: 0.6pt + black,
    )
    circle(
      (x-left-mid, y-top - f / 2),
      radius: 0.06,
      fill: white,
      stroke: 0.6pt + black,
    )

    // Dimensions: Depth & Height
    line(
      (x-left-start, y-bot),
      (x-left-start, y-bot - 0.6),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-left-end, y-bot),
      (x-left-end, y-bot - 0.6),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-left-start, y-bot - 0.6),
      (x-left-end, y-bot - 0.6),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.10,
      stroke: 0.6pt + black,
    )
    content((x-left-mid, y-bot - 0.9), text(size: 7pt)[$qty(152.4, "mm")$])

    line(
      (x-left-start, y-bot),
      (x-left-start - 0.6, y-bot),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-left-start, y-top),
      (x-left-start - 0.6, y-top),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-left-start - 0.6, y-bot),
      (x-left-start - 0.6, y-top),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.10,
      stroke: 0.6pt + black,
    )
    content(
      (x-left-start - 0.9, (y-bot + y-top) / 2),
      text(size: 7pt)[$qty(165.1, "mm")$],
      angle: 90deg,
    )

    // ==========================================
    // 2. REAR ELEVATION (Rear Closure: 35.7 x 165.1 mm)
    // ==========================================
    let x-rear-start = 5.8
    let x-rear-end = x-rear-start + w
    let x-rear-mid = (x-rear-start + x-rear-end) / 2

    // View Title
    content((x-rear-mid, y-top + 0.8), text(
      size: 8.5pt,
      weight: "bold",
    )[REAR ELEVATION])

    // Main Rear Closure Plate
    rect(
      (x-rear-start, y-bot),
      (x-rear-end, y-top),
      fill: luma(235),
      stroke: 1.2pt + black,
    )

    // Flanges (Top, Bottom, Right folded 90 deg inward)
    line((x-rear-start, y-top - f), (x-rear-end, y-top - f), stroke: (
      paint: luma(120),
      thickness: 0.7pt,
      dash: "dashed",
    ))
    line((x-rear-start, y-bot + f), (x-rear-end, y-bot + f), stroke: (
      paint: luma(120),
      thickness: 0.7pt,
      dash: "dashed",
    ))
    line((x-rear-end - f, y-bot), (x-rear-end - f, y-top), stroke: (
      paint: luma(120),
      thickness: 0.7pt,
      dash: "dashed",
    ))

    // DB-25 Cutout at Y = 55.0 mm (Centered)
    let db25-w = 26.0 * s
    let db25-h = 11.0 * s
    rect(
      (x-rear-start + db25-x - db25-w / 2, db25-y - db25-h / 2),
      (x-rear-start + db25-x + db25-w / 2, db25-y + db25-h / 2),
      fill: white,
      stroke: 0.9pt + black,
    )
    content((x-rear-start + db25-x, db25-y), text(
      size: 5.5pt,
      weight: "bold",
    )[DB-25])

    // BNC Cutout at Y = 130.0 mm (Centered, Facultative)
    let bnc-r = 6.0 * s
    circle(
      (x-rear-start + db25-x, bnc-y),
      radius: bnc-r,
      fill: white,
      stroke: 0.9pt + black,
    )
    content((x-rear-start + db25-x, bnc-y), text(
      size: 5pt,
      weight: "bold",
    )[BNC])

    // Cutout Centerline Indicators & Heights
    line((x-rear-start - 0.2, db25-y), (x-rear-end + 0.6, db25-y), stroke: (
      paint: luma(160),
      thickness: 0.4pt,
      dash: "dash-dotted",
    ))
    line((x-rear-start - 0.2, bnc-y), (x-rear-end + 0.6, bnc-y), stroke: (
      paint: luma(160),
      thickness: 0.4pt,
      dash: "dash-dotted",
    ))

    // Width Dimension (35.7 mm)
    line(
      (x-rear-start, y-bot),
      (x-rear-start, y-bot - 0.6),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-rear-end, y-bot),
      (x-rear-end, y-bot - 0.6),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-rear-start, y-bot - 0.6),
      (x-rear-end, y-bot - 0.6),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.10,
      stroke: 0.6pt + black,
    )
    content((x-rear-mid, y-bot - 0.9), text(size: 7pt)[$qty(35.7, "mm")$])

    // Height Dimensions: DB-25 (55 mm) & BNC (130 mm)
    line(
      (x-rear-end, y-bot),
      (x-rear-end + 0.6, y-bot),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-rear-end + 0.6, y-bot),
      (x-rear-end + 0.6, db25-y),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.10,
      stroke: 0.6pt + black,
    )
    content(
      (x-rear-end + 0.9, db25-y / 2),
      text(size: 6.5pt)[$qty(55.0, "mm")$],
      angle: -90deg,
    )

    line(
      (x-rear-end + 0.6, db25-y),
      (x-rear-end + 0.6, bnc-y),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.10,
      stroke: 0.6pt + black,
    )
    content(
      (x-rear-end + 0.9, (db25-y + bnc-y) / 2),
      text(size: 6.5pt)[$qty(130.0, "mm")$],
      angle: -90deg,
    )

    // ==========================================
    // 3. ISOMETRIC VIEW (3D Sheet Metal Structure)
    // ==========================================
    let iso-x0 = 12.5
    let iso-y0 = -1

    // Helper function for isometric projection
    // X = Width (0..35.7 mm), Y = Height (0..165.1 mm), Z = Depth (0..152.4 mm)
    let p(x-mm, y-mm, z-mm) = {
      let px = iso-x0 + (x-mm * 0.866 - z-mm * 0.866) * s
      let py = iso-y0 + (y-mm + x-mm * 0.5 + z-mm * 0.5) * s
      return (px, py)
    }

    // View Title
    content((iso-x0, y-top + 0.8), text(
      size: 8.5pt,
      weight: "bold",
    )[ISOMETRIC VIEW])

    // Left Wall Outer Face (Z=0..152.4, Y=0..165.1, X=0)
    line(
      p(0, 0, 0),
      p(0, 0, 152.4),
      p(0, 165.1, 152.4),
      p(0, 165.1, 0),
      close: true,
      fill: luma(240),
      stroke: 1pt + black,
    )

    // Rear Closure Outer Face (X=0..35.7, Y=0..165.1, Z=0)
    line(
      p(0, 0, 0),
      p(35.7, 0, 0),
      p(35.7, 165.1, 0),
      p(0, 165.1, 0),
      close: true,
      fill: luma(225),
      stroke: 1pt + black,
    )

    // Folded Inward Flanges (8 mm width)
    // Left Wall Top Flange
    line(
      p(0, 165.1, 0),
      p(0, 165.1, 152.4),
      p(8.0, 165.1, 152.4),
      p(8.0, 165.1, 0),
      close: true,
      fill: luma(210),
      stroke: 0.8pt + black,
    )

    // Left Wall Front Flange
    line(
      p(0, 0, 152.4),
      p(0, 165.1, 152.4),
      p(8.0, 165.1, 152.4),
      p(8.0, 0, 152.4),
      close: true,
      fill: luma(215),
      stroke: 0.8pt + black,
    )

    // Rear Wall Bottom Flange
    line(
      p(0, 0, 0),
      p(0, 0, 8.0),
      p(35.7, 0, 8.0),
      p(35.7, 0, 0.0),
      close: true,
      fill: luma(200),
      stroke: 0.8pt + black,
    )

    // Left Wall Bottom Flange
    line(
      p(0, 0, 0),
      p(0, 0, 152.4),
      p(8.0, 0, 152.4),
      p(8.0, 0, 8),
      close: true,
      fill: luma(210),
      stroke: 0.8pt + black,
    )

    // Rear Wall Right Flange
    line(
      p(35.7, 0, 0),
      p(35.7, 165.1, 0),
      p(35.7, 165.1, 8.0),
      p(35.7, 0, 8.0),
      close: true,
      fill: luma(200),
      stroke: 0.8pt + black,
    )

    // Rear Wall Top Flange
    line(
      p(0, 165.1, 0),
      p(0, 165.1, 8.0),
      p(35.7, 165.1, 8.0),
      p(35.7, 165.1, 0.0),
      close: true,
      fill: luma(200),
      stroke: 0.8pt + black,
    )

    // DB-25 Cutout on Rear Face (Z=0)
    let db-w2 = 13.0
    let db-h2 = 5.5
    line(
      p(17.85 - db-w2, 55.0 - db-h2, 0),
      p(17.85 + db-w2, 55.0 - db-h2, 0),
      p(17.85 + db-w2, 55.0 + db-h2, 0),
      p(17.85 - db-w2, 55.0 + db-h2, 0),
      close: true,
      fill: white,
      stroke: 0.8pt + black,
    )

    // BNC Cutout on Rear Face (Z=0)
    line(
      p(17.85 - 4.5, 130.0 - 4.5, 0),
      p(17.85 + 4.5, 130.0 - 4.5, 0),
      p(17.85 + 4.5, 130.0 + 4.5, 0),
      p(17.85 - 4.5, 130.0 + 4.5, 0),
      close: true,
      fill: white,
      stroke: 0.8pt + black,
    )

    // PEM Nut Threaded Insert Points (Visual markers on top/front flanges)
    circle(p(4.0, 165.1, 30.0), radius: 0.05, fill: black)
    circle(p(4.0, 165.1, 120.0), radius: 0.05, fill: black)
    circle(p(4.0, 0, 30.0), radius: 0.05, fill: black)
    circle(p(4.0, 0, 120.0), radius: 0.05, fill: black)
    circle(p(4.0, 30.0, 152.4), radius: 0.05, fill: black)
    circle(p(4.0, 135.0, 152.4), radius: 0.05, fill: black)
    circle(p(35.7 - 4.0, 30.0, 0), radius: 0.05, fill: black)
    circle(p(35.7 - 4.0, 135.0, 0), radius: 0.05, fill: black)
    circle(p(17.85, 165.1, 4.0), radius: 0.05, fill: black)
    circle(p(17.85, 0, 4.0), radius: 0.05, fill: black)

    // Masked Unpainted Area Callout Annotation
    line(
      p(4.0, 165.1, 75.0),
      (iso-x0 + 1.2, y-top),
      stroke: 0.5pt + black,
    )
    content(
      (iso-x0 + 1.25, y-top - 0.3),
      text(size: 6.5pt)[Unpainted EMI flange \
        contact area (PEM nuts \
        fitted)],
      anchor: "south-west",
    )
  }),
  caption: [Cassette L-Channel structural spine technical drawings showing orthographic projections (left and rear elevations) and 3D isometric sheet metal form.],
) <figure-cassette-lchannel-diagram>

/ Role: Structural spine. Holds the PCB and Front Panel.
/ Geometry:
  / Left wall ($qty(165.1, "mm") times qty(152.4, "mm")$): PCB mounts here.
  / Rear closure ($qty(165.1, "mm") times qty(35.7, "mm")$): Includes DB-25 and
    BNC cutouts.
    / DB-25 cutout: Center X: $qty(17.85, "mm")$ (centered). Center Y:
      $qty(55.0, "mm")$ from bottom edge.
    / BNC cutout: Center X: $qty(17.85, "mm")$ (centered). Center Y:
      $qty(130.0, "mm")$ from bottom edge.
      / Facultative: Required only for modules utilizing the Master Oscillator.
        If absent, the steel surface remains solid to maintain maximum shielding
        integrity.
/ Flanges (The Mounting Points):
  - The Left Wall features Top, Bottom and Front flanges folded
    $qty(90, "degree")$ inward.
  - The Rear Wall features Top, Bottom, and Right flanges folded
    $qty(90, "degree")$ inward.
  - The flanges are $qty(8, "mm")$.
/ Threads: These flanges must be fitted with M3 Press-Fit Threaded Inserts (PEM
  Nuts) or similar clinching fasteners.
  / Why: The $qty(1.2, "mm")$ steel is too thin to tap reliably for repeated
    use. Inserts ensure the threads don't strip after years of maintenance.
/ Finish: The outer face of these flanges must be masked (unpainted) to ensure
  electrical contact with the U-Channel and the front panel.

===== U-channel (cover) <u-channel-cover>

#figure(
  cetz.canvas({
    import cetz.draw: *

    // Scale factor: 1 mm = 0.060 drawing units
    let s = 0.060

    let h = 165.1 * s // 4.953 mm
    let d = 152.4 * s // 4.572 mm
    let w = 35.7 * s // 1.071 mm
    let f = 8.0 * s // 0.240 mm (8 mm flange overlap)
    let t = 1.2 * s // Sheet metal thickness (1.2 mm)

    let y-bot = 0
    let y-top = h

    // ==========================================
    // 1. FRONT ELEVATION (U-Profile End View: 35.7 x 165.1 mm)
    // ==========================================
    let x-front-start = 0
    let x-front-end = x-front-start + w
    let x-front-mid = (x-front-start + x-front-end) / 2

    // View Title
    content((x-front-mid, y-top + 0.8), text(
      size: 8.5pt,
      weight: "bold",
    )[FRONT ELEVATION])

    // U-Channel Sheet Metal Cross-Section Outline
    // Top Limb
    rect(
      (x-front-start, y-top - t),
      (x-front-end, y-top),
      fill: luma(210),
      stroke: 0.8pt + black,
    )
    // Right Side Wall
    rect(
      (x-front-end - t, y-bot),
      (x-front-end, y-top),
      fill: luma(230),
      stroke: 0.8pt + black,
    )
    // Bottom Limb
    rect(
      (x-front-start, y-bot),
      (x-front-end, y-bot + t),
      fill: luma(210),
      stroke: 0.8pt + black,
    )

    // Inner Cavity Hatch/Indicator Line
    line(
      (x-front-start, y-bot + t),
      (x-front-end - t, y-bot + t),
      (x-front-end - t, y-top - t),
      (x-front-start, y-top - t),
      stroke: (paint: luma(140), thickness: 0.5pt, dash: "dotted"),
    )

    // Front Width Dimension (35.7 mm)
    line(
      (x-front-start, y-bot),
      (x-front-start, y-bot - 0.6),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-front-end, y-bot),
      (x-front-end, y-bot - 0.6),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-front-start, y-bot - 0.6),
      (x-front-end, y-bot - 0.6),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.10,
      stroke: 0.6pt + black,
    )
    content((x-front-mid, y-bot - 0.9), text(size: 7pt)[$qty(35.7, "mm")$])

    // Front Height Dimension (165.1 mm)
    line(
      (x-front-start, y-bot),
      (x-front-start - 0.6, y-bot),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-front-start, y-top),
      (x-front-start - 0.6, y-top),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-front-start - 0.6, y-bot),
      (x-front-start - 0.6, y-top),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.10,
      stroke: 0.6pt + black,
    )
    content(
      (x-front-start - 0.9, (y-bot + y-top) / 2),
      text(size: 7pt)[$qty(165.1, "mm")$],
      angle: 90deg,
    )

    // ==========================================
    // 2. RIGHT ELEVATION (Inner Face View: 152.4 x 165.1 mm)
    // ==========================================
    let x-right-start = 3.5
    let x-right-end = x-right-start + d
    let x-right-mid = (x-right-start + x-right-end) / 2

    // View Title
    content((x-right-mid, y-top + 0.8), text(
      size: 8.5pt,
      weight: "bold",
    )[RIGHT ELEVATION (INNER FACE)])

    // Main Right Wall Sheet Metal Surface
    rect(
      (x-right-start, y-bot),
      (x-right-end, y-top),
      fill: luma(245),
      stroke: 1.2pt + black,
    )

    // Masked Unpainted Perimeter Area (8mm border where it mates with L-channel flanges)
    rect(
      (x-right-start + f, y-bot + f),
      (x-right-end - f, y-top - f),
      fill: luma(230),
      stroke: (paint: luma(130), thickness: 0.7pt, dash: "dashed"),
    )
    content(
      (x-right-mid, (y-bot + y-top) / 2),
      text(size: 7.5pt, fill: luma(100))[Painted Central Surface],
    )

    // Countersunk Through-Holes (Crosshair + concentric circles for 90-deg countersink)
    let draw-csink(cx, cy) = {
      circle((cx, cy), radius: 0.10, fill: white, stroke: 0.6pt + black)
      circle((cx, cy), radius: 0.05, fill: luma(180), stroke: 0.4pt + black)
      line((cx - 0.13, cy), (cx + 0.13, cy), stroke: 0.3pt + luma(120))
      line((cx, cy - 0.13), (cx, cy + 0.13), stroke: 0.3pt + luma(120))
    }

    // Top & Bottom Edge Countersunk Hole Pattern (matching top/bottom flanges)
    draw-csink(x-right-start + 30.0 * s, y-top - f / 2)
    draw-csink(x-right-start + 122.4 * s, y-top - f / 2)
    draw-csink(x-right-start + 30.0 * s, y-bot + f / 2)
    draw-csink(x-right-start + 122.4 * s, y-bot + f / 2)

    // Front & Rear Edge Countersunk Hole Pattern
    draw-csink(x-right-start + f / 2, y-bot + 30.0 * s)
    draw-csink(x-right-start + f / 2, y-top - 30.0 * s)
    draw-csink(x-right-end - f / 2, y-bot + 30.0 * s)
    draw-csink(x-right-end - f / 2, y-top - 30.0 * s)

    // Depth Dimension (152.4 mm)
    line(
      (x-right-start, y-bot),
      (x-right-start, y-bot - 0.6),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-right-end, y-bot),
      (x-right-end, y-bot - 0.6),
      stroke: 0.4pt + luma(140),
    )
    line(
      (x-right-start, y-bot - 0.6),
      (x-right-end, y-bot - 0.6),
      mark: (start: "stealth", end: "stealth"),
      mark-size: 0.10,
      stroke: 0.6pt + black,
    )
    content((x-right-mid, y-bot - 0.9), text(size: 7pt)[$qty(152.4, "mm")$])

    // Masked Border Callout Annotation
    line(
      (x-right-start + f / 2, y-top - 15.0 * s),
      (x-right-start - 0.5, y-top - 1.0),
      stroke: 0.5pt + black,
    )
    content(
      (x-right-start - 0.5, y-top),
      text(size: 6.5pt)[Masked unpainted perimeter \
        (8 mm EMI contact area)],
      anchor: "south-east",
      angle: 90deg,
    )
  }),
  caption: [Cassette U-Channel cover technical drawings showing Front Elevation (profile) and Right Elevation (inner face showing masked unpainted EMI perimeter and countersunk hole grid).],
) <figure-cassette-uchannel-diagram>

/ Role: EMI Shielding and Protection.
/ Geometry:
  / Top ($qty(35.7, "mm") times qty(152.4, "mm")$): vented
  / Right side wall ($qty(165.1, "mm") times qty(152.4, "mm")$):
  / Bottom ($qty(35.7, "mm") times qty(152.4, "mm")$): vented
/ Holes: Features Countersunk Through-Holes corresponding to the L-Channel's
  threaded inserts.
/ Finish: The inner face contact area must be masked (unpainted).

===== Front panel <front-panel>

#figure(
  image("pictures/front-panel-geometry.svg"),
  caption: [Front channel construction],
) <figure-front-channel-construction>

/ Geometry: $qty(177.8, "mm") times qty(38.0, "mm")$, body section
  $qty(165.1, "mm")$
/ Holes: Features Countersunk Through-Holes corresponding to the L-Channel's
  threaded inserts.
/ Finish: The inner face contact area must be masked (unpainted).

===== Fasteners <fasteners>

/ Type: M3 Countersunk (Flat Head) Screws (Black Oxide).
/ Flushness: Screw heads must sit flush with the external surface to prevent
  snagging when sliding the module into the rack.
/ Spacing: Screws should be spaced no more than $qty(40, "mm")$ apart along the
  seams to ensure the "slot antenna" effect does not compromise shielding at
  high frequencies ($gt qty(1, "GHz")$). There are $5$ screws per vertical
  flange, seam, and $4$ per horizontal seam.

===== Grounding requirements <cassette-grounding-requirements>

To prevent the cassette from acting as a floating antenna, the enclosure must
maintain a low-impedance electrical connection to the chassis earth. The
connection is made at the DB-25 port and the rear BNC connector shell if
present. The mounting holes must be masked during powder coating, or star
washers be used to screw it in place.

The BNC connector shell must be bonded to the steel cassette (masking required).
The signal carried by the BNC (10MHz) is referenced to the BNC shell (Chassis
Earth/RF Ground), not AGND, to prevent high-frequency injection into the
precision analog ground plane.

To ensure the connections actually block noise (RF), masking is mandatory: The
powder coat is an insulator. There must be masking (no paint) on the outer face
of all L-Channel flanges and the corresponding inner face of the U-Channel and
Panel.

When the screws are tightened, metal-to-metal contact must be achieved around
the entire perimeter of the seam. If paint blocks this contact, the shielding
will fail, degrading the SNR below the $qty(90, "dB")$ target.

==== Internal dimensions <cassette-internal-dimensions>

#figure(
  table(
    columns: 2,
    table.header([Dimension], [Value]),
    [Height], [$qty(162.7, "mm")$],
    [Width], [$qty(35.6, "mm")$],
    [Depth], [$qty(150, "mm")$],
  ),
  caption: [Cassette internal dimensions],
) <table-cassette-internal-dimensions>

==== Ventilation <cassette-ventilation>

Top and bottom faces include ventilation slots for convective cooling while
maintaining EMI shielding.

#figure(
  image("pictures/ventilation.svg"),
  caption: [Cassette ventilation],
) <figure-cassette-ventilation>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Slot size], [$qty(2.5, "mm") times qty(10, "mm")$],
    [Slot orientation], [Length parallel to cassette depth],
    [Rows], [$5$],
    [Row pitch], [$qty(5, "mm")$],
    [Columns], [$12$],
    [Column pitch], [$qty(12, "mm")$],
    [Slots per face], [$60$],
    [Open area], [$approx qty(28, "percent")$],
    [Shielding effectiveness], [$gt qty(20, "dB") "to" qty(1, "GHz")$],
  ),
  caption: [Cassette ventilation specifications],
) <table-cassette-ventilation>

==== DB-25 connector cutout <db-25-connector-cutout>

#figure(
  image("pictures/db-25-connector-cutout.svg"),
  caption: [DB-25 connector cutout],
) <figure-db-25-connector-cutout>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Shape], [D-shaped (standard DB-25 profile)],

    [D-opening width], [$qty(33.3, "mm")$],

    [D-opening height], [$qty(12.5, "mm")$],

    [Mounting hole spacing], [$qty(24.99, "mm")$],

    [Mounting hole size], [$diameter qty(3.2, "mm")$],

    [Center X], [$qty(17.85, "mm")$ from either edge],

    [Center Y], [$qty(82.5, "mm")$ from top/bottom (centered on $qty(165.1, "mm")$)],

    [Connector assembly], [Panel mount with solder cups],

    [Position], [Centered on rear closure],
  ),
  caption: [Cassette DB-25 connector cutout specifications],
) <table-cassette-db-25-connector-cutout>

==== PCB dimensions <cassette-pcb-dimensions>

The PCB is sized to fit within the L-Channel side wall while leaving clearance
for the interlocking U-Channel flanges and internal cabling.

/ PCB Height: $qty(155.0, "mm")$
/ PCB Depth: $qty(125.0, "mm")$
/ PCB Thickness: $qty(1.6, "mm")$ (Standard FR-4)
/ Orientation: Mounted vertically on the internal Left Wall.

===== PCB mounting geometry <cassette-pcb-mounting-geometry>

The cassette Left Wall shall feature four ($4$) permanently attached female
threaded standoffs (M3) to accept the PCB.

/ Standoff Type: M3 Thread, 6mm Height (swaged or welded to the steel wall).
/ Mounting Pattern: Rectangular, centered on the cassette side wall.
  / Vertical Spacing (Y): $qty(135.0, "mm")$
  / Horizontal Spacing (X): $qty(105.0, "mm")$
/ Origin Reference: Pattern is centered relative to the internal side wall
  dimensions ($qty(165.1, "mm") times qty(150, "mm")$).

===== Keep-out zones <cassette-pcb-keep-out-zones>

To prevent electrical shorts against the steel chassis or mechanical
interference:

/ Perimeter Clearance: A 5mm component-free zone must be maintained along all
  four edges of the PCB.
/ Height Clearance: Components taller than 30mm are prohibited to ensure airflow
  and prevent shorting against the opposing Right Wall (total internal width is
  $qty(35.7, "mm")$. If tall components must be used, they must be assembled
  parallel to the PCB.

===== Interconnect layout (wire harness strategy)
<interconnect-layout-wire-harness-strategy>

Since the DB-25 is panel-mounted with solder cups and controls are on the front
panel, the PCB layout must optimize cable routing to minimize noise pickup and
maximize air flow.

/ Zone A (Rear - Power):
  / Function: Connection to the rear DB-25 backplane connector.
  / Location: Rear $qty(20, "mm")$ of the PCB.
  / Connector Type: Pluggable terminal block (e.g., Phoenix Contact
    $qty(3.5, "mm")$) or latching header (e.g., Molex KK $qty(3.96, "mm")$).
    Direct soldering of flying leads to the PCB is discouraged to maintain
    repairability.
  / Pinout: Must match the standard SAME Power Distribution definition.
/ Zone B (Front - I/O):
  / Function: Connection to Front Panel Banana Jacks and Potentiometers.
  / Location: Front $qty(20, "mm")$ of the PCB.
  / Routing: Cables should form a neat loom transitioning from the PCB edge to
    the panel components.
  / Service Loop: All internal cabling must have a service loop of
    $plus qty(20, "mm")$ to allow the PCB to be unscrewed and slightly lifted
    without desoldering.

===== Grounding & Isolation Strategy
<cassette-pcb-grounding-and-isolation-strategy>

To maintain the strict separation of Analog Ground (AGND) and Chassis Earth, the
PCB must be electrically isolated from the steel cassette.

/ PCB Mounting Holes: Must be unplated and isolated from all internal ground
  planes (AGND/DGND). The metal standoffs serve only as mechanical support, not
  electrical conductors for the circuit.
/ Cassette Earth Path: The steel cassette connects to Chassis Earth exclusively
  via the rear DB-25 Connector.
  / Implementation: The DB-25 panel-mount connector must have a conductive metal
    shell. When mounted to the rear steel panel, the connector shell (and Pin
    $25$) creates the bond between the cable shield and the cassette body.
  / Verification: Resistance between the DB-25 Shell and any point on the
    cassette powder-coat-free zones must be $lt qty(0.1, "ohm")$.

=== PCB <pcb>

==== Overview <pcb-overview>

Module PCBs mount vertically within the L-channel, attached to the left side
wall via standoffs. The PCB connects to the front panel (banana jacks, controls)
via wire harnesses and to the power distribution board via the rear DB-25
connector.

==== Standard dimensions <pcb-standard-dimensions>

#figure(
  table(
    columns: 4,
    table.header([Parameter], [Value], [Tolerances], [Notes]),
    [Height], [$qty(155.0, "mm")$], [$plus.minus qty(0.2, "mm")$], [Vertical dimension when mounted],

    [Depth], [$qty(125.0, "mm")$], [$plus.minus qty(0.2, "mm")$], [Front-to-rear dimension],

    [Thickness], [$qty(1.6, "mm")$], [$plus.minus qty(0.15, "mm")$], [Standard 4-layer stackup],

    [Corner radius], [$qty(3.0, "mm")$], [$plus.minus qty(0.5, "mm")$], [All four corners, for insertion clearance],
  ),
  caption: [PCB standard dimensions],
) <table-pcb-standard-dimensions>

==== Board stackup <pcb-board-stackup>

All SAME module PCBs shall use a 4-layer stackup: This allows proper ground
management, while remaining easy to solder with standard equipment.

#figure(
  table(
    columns: 4,
    table.header([Layer], [Function], [Copper weight], [Notes]),
    [L1 (top)],
    [Signal + components],
    [$qty(1, "oz")$ ($qty(35, "um")$)],
    [Component side faces right (toward U-channel)],

    [L2 (inner 1)],
    [Ground plane],
    [$qty(1, "oz")$ ($qty(35, "um")$)],
    [Continuous AGND plane, split for DGND if needed],

    [L3 (inner 2)],
    [Power plane],
    [$qty(1, "oz")$ ($qty(35, "um")$)],
    [Split for $plus.minus qty(15, "V")$, $plus.minus qty(5, "V")$ rails],

    [L4 (bottom)],
    [Signal + earth ring],
    [$qty(1, "oz")$ ($qty(35, "um")$)],
    [Faces left wall (mounting side), digital traces if needed],
  ),
  caption: [PCB board stackup],
) <table-pcb-board-stackup>

/ Dielectric: FR-4, $"Tg" gt.eq qty(135, "dC")$

==== Surface finish <pcb-surface-finish>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Specification]),
    [Finish], [ENIG (Electroless Nickel Immersion Gold)],

    [Nickel thickness], [$qtyrange(3, 5, "um")$],

    [Gold thickness], [$qtyrange(0.05, 0.1, "um")$ ($qtyrange(1, 2, "micro inch")$)],

    [Solder mask], [Matte black (both sides)],

    [Silkscreen], [White (both sides)],
  ),
  caption: [PCB surface finish],
) <table-pcb-surface-finish>

===== Rationale <pcb-surface-finish-rationale>

ENIG provides excellent corrosion resistance for the 50-year service life
target. A flat surface ensures reliable soldering of precision components. Gold
does not oxidize, maintaining consistent contact resistance at test points.

Black solder mask reduces light reflectivity (some precision semiconductors are
photosensitive).

==== Earth ring <pcb-earth-ring>

The PCB shall include a Chassis Earth ring around the perimeter of the bottom
layer (L4). This ring provides a defined path for any capacitively-coupled noise
to drain to chassis earth rather than coupling into signal traces.

===== Geometry <pcb-earth-ring-geometry>

#figure(
  table(
    columns: 3,
    table.header([Parameter], [Value], [Notes]),
    [Width], [$qty(3.0, "mm")$], [Continuous copper pour],
    [Clearance from edge], [$qty(0.5, "mm")$], [Manufacturing tolerance],
    [Clearance to inner circuitry], [$qty(2.0, "mm")$], [Isolation gap],
    [Layer], [L4 (bottom) only], [Faces mounting wall],
  ),
  caption: [PCB earth ring geometry],
) <table-pcb-earth-ring-geometry>

===== Connection <pcb-earth-ring-connection>

The earth ring shall not connect to AGND or DGND on the PCB. It connects to
Chassis Earth exclusively through the pin 25 of the DB-25 power distributor via
a trace on L4.

===== Mounting holes details <pcb-earth-ring-mounting-holes-details>

The four mounting holes shall be:

- Unplated, isolated through-holes, $diameter qty(3.2, "mm")$ (M3 clearance).
- Not connected to any layer (no vias to L1, L2, L3, L4).

==== Ground planes <pcb-ground-planes>

===== AGND plane <pcb-ground-planes-agnd-plane>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Layer], [L2 (inner 1)],
    [Coverage], [Minimum $qty(85, "percent")$ of signal area],
    [Splits], [Only if DGND zone required],
    [Connection], [Via stitching to AGND traces & pads on L1 and L4],
  ),
  caption: [PCB AGND plane],
) <table-pcb-ground-planes-agnd-plane>

The AGND plane provides:
- Low-impedance return path for analog signals,
- Shielding between signal layers,
- Thermal spreading.

===== DGND zone (if needed) <pcb-ground-planes-dgnd-zone>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Location], [Defined zone on L2],
    [Separation], [$qty(2, "mm")$ gap from AGND plane],
    [Connection], [To the DGND pins of the power distributor],
    [Via stitching], [Only within DGND zone],
  ),
  caption: [PCB DGND zone],
) <table-pcb-ground-planes-dgnd-zone>

==== Power planes <pcb-power-planes>

Layer 3 is divided into power distribution zones:

#figure(
  table(
    columns: 3,
    table.header([Zone], [Rail], [Typical area]),
    [Zone 1], [$plus qty(15, "V")$], [$qtyrange(30, 40, "percent")$],

    [Zone 2], [$qty(-15, "V")$], [$qtyrange(30, 40, "percent")$],

    [Zone 3], [$plus qty(5, "V")$ (if needed)], [$qtyrange(10, 15, "percent")$],

    [Zone 4], [$qty(-5, "V")$ (if needed)], [$qtyrange(10, 15, "percent")$],
  ),
  caption: [PCB power planes],
) <table-pcb-power-planes>

Design rules:
- Miminum $qty(2, "mm")$ clearance between power zones,
- Star distribution from power enty point,
- Bulk decoupling capacitors from power enty point,
- Local decoupling at each IC.

==== Mounting strategy <pcb-mounting-strategy>

The PCB mounts to the L-channel left wall via four standoffs.

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Standoff thread], [$M 3$],
    [Standoff height], [$qty(6, "mm")$],
    [Standoff type], [Female threaded, swaged or welded to L-channel],
    [Mounting screw], [$M 3 times qty(8, "mm")$ pan head],
  ),
  caption: [PCB mounting strategy: standoffs],
) <table-pcb-mounting-strategy-standoffs>

===== Mounting holes pattern <pcb-mounting-strategy-mounting-holes-pattern>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Pattern], [Rectangular, $4$ holes],
    [Horizontal spacing (X)], [$qty(105.0, "mm")$],
    [Vertical spacing (Y)], [$qty(155.0, "mm")$],
    [Hole diameter], [$diameter qty(3.2, "mm")$ ($M 3$ clearance)],
    [Hole plating], [Unplated, isolated],
  ),
  caption: [PCB mounting strategy: mounting holes],
) <table-pcb-mounting-strategy-mounting-holes-pattern>

====== Positions <pcb-mounting-strategy-mounting-holes-positions>

#figure(
  table(
    columns: 3,
    table.header([Hole], [X], [Y]),
    [1 (bottom-left)], [$qty(10.00, "mm")$], [$qty(10.00, "mm")$],
    [2 (bottom-right)], [$qty(115.00, "mm")$], [$qty(10.00, "mm")$],
    [3 (top-left)], [$qty(10.00, "mm")$], [$qty(145.00, "mm")$],
    [4 (top-right)], [$qty(115.00, "mm")$], [$qty(145.00, "mm")$],
  ),
  caption: [PCB mounting strategy: mounting holes positions],
)

==== Keep-out zones <pcb-keep-out-zones>

===== Perimeter keep-out <pcb-keep-out-zones-perimeter-keep-out>

#figure(
  table(
    columns: 3,
    table.header([Parameter], [Value], [Notes]),
    [Width], [$qty(5.0, "mm")$], [All four edges],
    [Applies to], [Components and tall traces], [Solder mask and silkscreen allowed],

    [Reason], [Clearance for cassette walls and earth ring], [],
  ),
  caption: [PCB keep-out zones: perimeter keep-out],
) <table-pcb-keep-out-zones-perimeter-keep-out>

===== Mounting holes keep-out <pcb-keep-out-zones-mounting-holes-keep-out>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Radius], [$qty(0.5, "mm")$ from hole center],
    [Applies to], [Components, traces, planes (except earth ring)],
  ),
  caption: [PCB keep-out zones: mounting holes keep-out],
) <table-pcb-keep-out-zones-mounting-holes-keep-out>

==== Interconnect zones <pcb-interconnect-zones>

===== Zone A: power and master oscillator entry (rear) <pcb-interconnect-zones-zone-a>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Location], [Rear $qty(20, "mm")$ of PCB ($Y = qtyrange(0, 20, "mm")$)],

    [Function], [Connection to DB-25 backplane connector and rear BNC],
    [Connector],
    [
      / Power: pluggable terminal block (e.g. Phoenix Contact MSTB $qty(3.5, "mm")$ or latching header (e.g Molex KK $qty(3.96, "mm")$).
      / Master oscillator (optional): The rear BNC connects to the PCB via a short ($lt qty(50, "mm")$) $qty(50, "ohm")$ coaxial pigtail (RG-174 or RG-316) soldered to dedicated RF pads or a u.FL/SMA connector on the PCB edge.
    ],

    [Wire gauge], [$qtyrange(22, 24, "AWG")$ for power, $qty(26, "AWG")$ for signals],
  ),
  caption: [PCB interconnect zones: zone A],
) <table-pcb-interconnect-zones-zone-a>

====== Pin assignment <pcb-interconnect-zones-zone-a-pin-assignment>

The PCB connector shall provide access to all power rails in a logical grouping:

#figure(
  table(
    columns: 3,
    table.header([Position], [Signal], [Recommended wire color]),
    [1], [$plus qty(15, "V")$], [Red],
    [2], [$qty(-15, "V")$], [Orange],
    [3], [AGND], [Black],
    [4], [$plus qty(10, "V")$ force], [White],
    [5], [$plus qty(10, "V")$ sense], [White / red stripe],
    [6], [$qty(-10, "V")$ force], [Grey],
    [7], [$qty(-10, "V")$ sense], [Gred / red stripe],
    [8], [$plus qty(5, "VD")$], [Yellow],
    [9], [$qty(-5, "VD")$], [Blue],
    [10], [DGND], [Brown],
    [11], [Stagger], [Purple],
    [12], [Chassis Earth], [Green / yellow stripe],
  ),
  caption: [PCB interconnect zones: zone A pin assignment],
) <table-pcb-interconnect-zones-zone-a-pin-assignment>

Not all modules require all signals. Unused positions may be omitted from the
harness.

===== Zone B: front panel I/O <pcb-interconnect-zones-zone-b>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Location], [Front $qty(20, "mm")$ of PCB ($Y = qtyrange(135, 155, "mm")$)],

    [Function], [Connection to banana jacks and controls],
    [Connector], [Pin headers, terminal blocks, or direct solder pads],
    [Wire gauge], [$qtyrange(24, 25, "AWG")$],
  ),
  caption: [PCB interconnect zones: zone B],
) <table-pcb-interconnect-zones-zone-b>

Design guidelines:
- Group outputs on one side, inputs on the other,
- Maintain signal flow from right to left (input #sym.arrow.r processing
  #sym.arrow.r output),
- Include test points for each signal node.

===== Service loop requirements <pcb-interconnect-zones-zone-b-service-loop-requirements>

All internal wiring shall include a service loop of minimum $qty(20, "mm")$
additional length. This allows the PCB to be:
- Unscrewed from standoffs,
- Tilted or lifted for inspection,
- Accessed for rework.

Without disconnecting the wire harnesses.

==== Silkscreen requirements <pcb-silkscreen-requirements>

===== Component side (L1 - top) <pcb-silkscreen-requirements-l1>

#figure(
  table(
    columns: 2,
    table.header([Element], [Requirement]),
    [Reference designators], [All components labeled($R_"bias"$, $C_"bulk"$, $U_"buf"$, etc.)],

    [Polarity marks], [All polarized components (diodes, electrolytics, ICs, etc.)],

    [Pin 1 indicators], [All ICs and connectors],
    [Assembly notes], [Tier-specific component values (if applicable)],
    [Test points], [Labeled with signal name],
  ),
  caption: [PCB silkscreen requirements: component side (L1 - top)],
) <table-pcb-silkscreen-requirements-l1>

Labels should be functional if possible, defaults to $R_1$, $C_1$, $U_1$, etc.
if there are space constraints.

===== Solder side (L4 - bottom) <pcb-silkscreen-requirements-l4>

#figure(
  table(
    columns: 2,
    table.header([Element], [Requirement]),
    [Board identification], [Module name, version, date],
    [SAME logo], [Mandatory],
    [Precision tier], ["$"EDU"$", "$"IND"$", or "$"MET"$" marking area],
    [Designer attribution], [Name, handle or logo],
    [License], ["$"CERN-OHL-S-2.0+"$"],
  ),
  caption: [PCB silkscreen requirements: solder side (L4 - bottom)],
) <table-pcb-silkscreen-requirements-l4>

==== Electrical testing <pcb-electrical-testing>

All PCBs shall pass the following tests before assembly:

#figure(
  table(
    columns: 2,
    table.header([Test], [Requirement]),
    [Isolation], [$gt qty(100, "mega ohm")$ between unconnected nets],
    [Continuity], [All nets per netlist],
    [Earth ring isolation], [$gt qty(100, "mega ohm")$ between earth ring and AGND/DGND],

    [Earth ring continuity],
    [$lt qty(1, "ohm")$ along entire earth ring perimeter (measure between opposite corners of the ring trace)],
  ),
  caption: [PCB electrical testing requirements],
) <table-pcb-electrical-testing-requirements>

=== Panels <panels>

==== Geometry <panels-geometry>

The front panel is a separate piece that attaches to the L-channel via countersunk screws.

#figure(
  table(
    columns: 3,
    table.header([Parameter], [Value], [Tolerance]),
    [Height], [$qty(177.8, "mm")$ ($qty(4, "U"), qty(7, "inch")$)], [$plus.minus qty(0.1, "mm")$],

    [Width], [$qty(38, "mm")$], [$plus 0.0 "/" qty(-0.1, "mm")$],
    [Thickness], [$qty(1.2, "mm")$], [$plus.minus qty(0.1, "mm")$],
    [Material], [DC01 cold-rolled steel], [N/A],
    [Finish], [Matte black powder coat (RAL 9005)], [N/A],
  ),
  caption: [Panels geometry],
) <table-panels-geometry>

===== Panels zones <panels-zones>

#figure(
  table(
    columns: 3,
    table.header([Zone], [Height range], [Function]),
    [Top lip], [$qtyrange(0, 6.35, "mm")$], [Extends above cassette body],

    [Body], [$qtyrange(6.35, 171.45, "mm")$], [Jack and control area],

    [Bottom lip], [$qtyrange(171.45, 177.8, "mm")$], [Extends below cassette body],
  ),
  caption: [Panels zones],
) <table-panels-zones>

==== Grid <panels-grid>

All panel-mounted components follow a $qty(0.75, "inch")$ ($qty(19.05, "mm")$)
grid for compatibility with standard banana jack spacing and shorting bars.

#figure(
  image("pictures/grid.svg"),
  caption: [Grid],
) <figure-grid>

===== Origin <panels-grid-origin>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Value]),
    [Origin X], [$qty(9.525, "mm")$ from left edge (first column center)],
    [Origin Y], [$qty(22.225, "mm")$ from top edge (first row center)],
    [Column pitch], [$qty(19.95, "mm")$ ($qty(0.75, "inch")$)],
    [Row pitch], [$qty(19.95, "mm")$ ($qty(0.75, "inch")$)],
    [Columns], [$2$],
    [Rows], [$8$],
  ),
  caption: [Panels grid orign],
) <table-panels-grid-origin>

===== Positions <panels-grid-positions>

#figure(
  table(
    columns: 5,
    table.header([Position], [Column], [Row], [X (from left)], [Y (from top)]),
    [A1], [$1$], [$1$], [$qty(9.525, "mm")$], [$qty(22.225, "mm")$],
    [B1], [$2$], [$1$], [$qty(28.575, "mm")$], [$qty(22.225, "mm")$],
    [A2], [$1$], [$2$], [$qty(9.525, "mm")$], [$qty(41.275, "mm")$],
    [B2], [$2$], [$2$], [$qty(28.575, "mm")$], [$qty(41.275, "mm")$],
    [A3], [$1$], [$3$], [$qty(9.525, "mm")$], [$qty(60.325, "mm")$],
    [B3], [$2$], [$3$], [$qty(28.575, "mm")$], [$qty(60.325, "mm")$],
    [A4], [$1$], [$4$], [$qty(9.525, "mm")$], [$qty(79.375, "mm")$],
    [B4], [$2$], [$4$], [$qty(28.575, "mm")$], [$qty(79.375, "mm")$],
    [A5], [$1$], [$5$], [$qty(9.525, "mm")$], [$qty(98.425, "mm")$],
    [B5], [$2$], [$5$], [$qty(28.575, "mm")$], [$qty(98.425, "mm")$],
    [A6], [$1$], [$6$], [$qty(9.525, "mm")$], [$qty(117.475, "mm")$],
    [B6], [$2$], [$6$], [$qty(28.575, "mm")$], [$qty(117.475, "mm")$],
    [A7], [$1$], [$7$], [$qty(9.525, "mm")$], [$qty(136.525, "mm")$],
    [B7], [$2$], [$7$], [$qty(28.575, "mm")$], [$qty(136.525, "mm")$],
    [A8], [$1$], [$8$], [$qty(9.525, "mm")$], [$qty(155.575, "mm")$],
    [B8], [$2$], [$8$], [$qty(28.575, "mm")$], [$qty(155.575, "mm")$],
  ),
  caption: [Panels grid positions],
) <table-panels-grid-positions>

===== Component placement rules <panels-grid-component-placement-rules>

#figure(
  table(
    columns: 3,
    table.header([Component], [Grid positions], [Hole size]),
    [$qty(4, "mm")$ banana jack], [Any], [$diameter qty(8.0, "mm")$],
    [$qty(6, "mm")$ potentiometer shaft], [Any], [$diameter qty(7.0, "mm")$],
    [$qty(3, "mm")$ LED], [Between grid positions], [$diameter qty(3.2, "mm")$],
    [Toggle switch], [Any], [Per switch specification],
    [Other components], [Centered on grid if possible], [Per component specification],
  ),
  caption: [Panels grid: component placement rules],
) <table-panels-grid-component-placement-rules>

====== Off-grid placements

+ Small indicators (LEDs) and labels may be placed between grid positions.
+ Non-specified components (controls, interface ports, etc.) should be centered
  on grid positions if possible, or centered on the panel.
+ Mounting screws for the panel (into L-channel flanges) are outside the grid
  area.

==== Labelling <panels-labelling>

All panels shall include clear, permanent labelling for user operation.

#figure(
  table(
    columns: 3,
    table.header([Element], [Requirement], [Location]),
    [Module name], [Mandatory], [Top lip],
    [Module mathematical function], [Recommended, when applicable], [Above row $1$],

    [Jack function], [Mandatory], [Above or beside jack],
    [Jack type], [Mandatory, color-coded jack], [At jack],
    [Signal flow], [Recommended, arrows or grouping], [As needed],
    [License], [Mandatory], [Below row $8$],
    [Version and tier], [Mandatory], [Bottom lip],
    [Module designer name or logo], [Optional], [Bottom lip],
    [Module builder name or logo], [Optional], [Bottom lip],
  ),
  caption: [Panels labelling requirements],
) <table-panels-labelling>

===== Jacks color coding <panels-jacks-color-coding>

#figure(
  table(
    columns: 2,
    table.header([Jack color], [Signal type]),
    [White], [Input (bipolar)],
    [Light blue], [Output (bipolar)],
    [Light yellow], [Output (unipolar)],
    [Red], [Output (gate)],
    [Yellow], [Output (reference $plus qty(10, "V")$)],
    [Blue], [Output (reference $qty(-10, "V")$)],
    [Black], [Analog ground],
  ),
  caption: [Jacks color coding],
) <table-panels-jacks-color-coding>

===== Use of colors in labels <panels-use-of-colors-in-labels>

The panel has a matte black background. To maintain legibility, all labels
should be white or off-white, with the following exceptions:
- For the designer or builder name or logo.
- When justified by the mathematical operation performed.

In any case, colors should be designed to offer sufficient contrast, and not
impact module usability by people suffering from color blindness.

===== Use of graphism and symbols in labels
<panels-use-of-graphism-and-symbols-in-labels>

We recommend the use of mathematical symbols and graphism when they illustrate
the functionality of the module. However, text labels should always be present
to express the jack functions.

===== Label method <panels-label-method>

Commercial, reference implementation or metrologic builds should always use
laser engraving or screen printing methods. Those have excellent durability and
legibility.

DIY builds can use UV-printed vinyl overlay method: it maintains good durability
and legibility while being more accessible.

===== Typography

Labels should be printed in a sans-serif typeface (DIN 1451, Eurostile,
Helvetica, etc.), except mathematical formulas. Module name size should be at
least $qty(4, "mm")$ height. Jack labels should be at least $qty(2, "mm")$
height.

== Chassis <chassis>

=== Overview <chassis-overview>

The chassis provides the mechanical and electrical infrastructure for housing
modules. It includes:
- Structural enclosure with EMI shielding,
- Cassette rail system for module installation and removal,
- Power distribution board with backplane connectors,
- Front panel with reference outputs and system controls,
- Thermal management provisions.

This specification defines interface requirements that any compliant chassis
must meet. Chassis may vary in capacity (number of module positions), form
factor (rack-mount, desktop, portable), and mounting style. The reference
implementation (@reference-implementation-chassis) describes a
$qty(19, "inch")$ $qty(4, "U")$ rack-mount chassis with $8$ module positions.

=== Dimensional requirements <chassis-dimensional-requirements>

#figure(
  image("pictures/chassis-module-loading.svg"),
  caption: [Chassis module loading dimensional requirements],
) <figure-chassis-dimensional-requirements>

==== Module interface dimensions <chassis-module-interface-dimensions>

All chassis must accommodate standard SAME cassettes. The following dimensions
are mandatory:

#figure(
  table(
    columns: 3,
    table.header([Parameter], [Value], [Notes]),
    [Module pitch], [$qty(38.1, "mm")$ ($qty(1.5, "inch")$)], [Center-to-center spacing],

    [Module opening height], [$qty(177.8, "mm")$ ($qty(4, "U"), qty(7, "inch")$)], [Panel visible area],

    [Module body clearance], [$qty(165.2, "mm")$], [Between top and bottom rails],

    [Module depth], [$qty(152.5, "mm")$], [Front panel to rear connector],
    [Rail-to-rail width], [$qty(38.1, "mm")$ ($qty(1.5, "inch")$)], [Center-to-center spacing],
  ),
  caption: [Module interface dimensions],
) <table-chassis-module-interface-dimensions>

==== Capacity <chassis-capacity>

Chassis capacity is defined by the number of module positions. There is no
minimum or maximum, but the following constraints apply:

#figure(
  table(
    columns: 3,
    table.header([Capacity], [Power budget], [Notes]),
    [Per module], [$qty(185, "mA") at plus.minus qty(15, "V")$], [Maximum per position],

    [Per module], [$qty(100, "mA") at plus.minus qty(5, "VD")$], [Maximum per position],

    [Total], [Scales with capacity], [Power distribution must support all positions],
  ),
  caption: [Chassis capacity power requirements],
) <table-chassis-capacity>

Designers should consider thermal dissipation when determining maximum capacity.

==== Clearances

The rear clearance (behind cassette) should be at least $qty(25, "mm")$, to
account for the DB-25 connector and cable bend radius.

=== Structural requirements <chassis-structural-requirements>

==== Material <chassis-material>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Requirement]),
    [Material], [Steel (recommended) or aluminum],
    [Minimum thickness], [$qty(1.5, "mm")$ (steel) or $qty(2.0, "mm")$ (aluminum)],

    [Finish], [Black powder coat or anodization, conductive areas masked],
  ),
  caption: [Chassis material requirements],
) <table-chassis-material>

Steel is preferred for magnetic shielding. Aluminum may be used where weight is
critical, with reduced magnetic shielding performance.

==== EMI shielding <chassis-emi-shielding>

A fully loaded chassis must form a continuous shielded enclosure:

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Requirement]),
    [Shielding effectiveness], [$gt qty(20, "dB"), qtyrange(80, 1000, "MHz")$],

    [Panel joints], [Metal-to-metal contact of conductive gasket],
    [Ventilation openings], [\ Maximum slot dimensions: $qty(10, "mm") times qty(2, "mm")$],

    [Cable entry], [Shield connectors or filtered feedthroughs],
  ),
  caption: [Chassis EMI shielding requirements],
) <table-chassis-emi-shielding>

==== Grounding <chassis-grounding>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Requirement]),
    [Chassis earth bonding], [All panels bonded to single earth point],
    [Earth impedance], [$gt qty(0.1, "ohm")$ between any two chassis points],
    [Safety earth], [Connected to mains earth via IEC inlet],
    [Module earth path], [Via DB-25 shell and pin 25],
  ),
  caption: [Chassis grounding requirements],
) <table-chassis-grounding>

=== Cassette rails <chassis-cassette-rails>

The rail system guides cassette insertion and provides retention.

==== Geometry <chassis-cassette-rails-geometry>

#figure(
  table(
    columns: 3,
    table.header([Parameter], [Value], [Notes]),
    [Rail height], [$qty(6.35, "mm")$ ($qty(0.25, "inch")$)], [Matches cassette lip height],

    [Channel width],
    [$qty(38.1, "mm")$ ($qty(1.5, "inch")$) $plus 0.2 "/" minus qty(0.0, "mm")$],
    [Accepts cassette body with clearance],

    [Channel depth], [$qty(5, "mm")$ minimum], [Guides cassette during insertion],

    [Rail length], [Full chassis depth], [Front to rear],
  ),
  caption: [Chassis cassette rails geometry],
) <table-chassis-cassette-rails-geometry>

==== Retention <chassis-cassette-rails-retention>

Cassettes must be retained to prevent accidental ejection during operation or
transport.

#figure(
  table(
    columns: 2,
    table.header([Method], [Requirement]),
    [Friction fit], [Acceptable for stationary installations],
    [Positive retention], [Required for portable or vibration-prone environments],

    [Front panel screws], [Optional, into chassis front rail],
  ),
  caption: [Chassis cassette retention requirements],
) <table-chassis-cassette-rails-retention>

Positive retention may be achieved via:
- Spring clips engaging cassette lips,
- Latching mechanisms.

==== Material <chassis-cassette-rails-material>

The rails must be of the same metal as the chassis, with a smooth, burr-free
finish; and bond to chassis earth.

They contribute to EMI shielding by closing the gap between cassette lips and
chassis structure.

=== Thermal management <chassis-thermal-management>

==== Cooling method <chassis-cooling-method>

Passive convection cooling is the baseline requirement. Forced-air cooling may
be added for high-density configurations.

#figure(
  table(
    columns: 2,
    table.header([Method], [Requirement]),
    [Passive (convection)], [Minimum for all chassis],
    [Active (forced air)], [Optional, for high-capacity or enclosed installations],
  ),
  caption: [Chassis cooling method requirements],
) <table-chassis-cooling-method>

==== Ventilation <chassis-ventilation>

Chassis ventilation must align with cassette ventilation slots to enable
chimney-effect airflow.

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Requirement]),
    [Bottom ventilation], [Required, aligned with cassette bottom vents],
    [Top ventilation], [Required, aligned with cassette top vents],
    [Slot dimensions], [$lt.eq qty(10, "mm") times qty(2, "mm")$ for EMI compliance],

    [Open area], [$gt.eq qty(20, "percent")$ of cassette footprint area],
  ),
  caption: [Chassis ventilation requirements],
) <table-chassis-ventilation>

==== Thermal limits <chassis-thermal-limits>

Inside the chassis cassette chamber, internal ambient temperature must not go
over $qty(50, "dC")$. If passive cooling cannot maintain thermal limits at full
capacity, forced-air cooling or reduced capacity is required.

=== Power distribution board <chassis-power-distribution-board>

The power distribution board generates and distributes all power rails to
module positions.

==== Functions <power-distribution-board-functions>

#figure(
  table(
    columns: 2,
    table.header([Function], [Requirement]),
    [AC-DC conversion],
    [Mains input to $plus.minus qty(15, "V")$, $plus.minus qty(5, "VD")$ rails. Can be external or internal],

    [Reference generation], [$plus.minus qty(10.0000, "V")$ precision references],

    [Master oscillator generation], [Generation of the $qty(10, "MHz")$ sine wave reference],

    [Distribution],
    [
      - One female DB-25 connector per module position,
      - One female isolated BNC connector per module position
    ],

    [Calibration], [Front-panel accessible switches],
    [Protection], [Overcurrent, overvoltage, thermal shutdown],
  ),
  caption: [Power distribution board functional requirements],
) <table-power-distribution-board-functions>

==== Power entry <power-distribution-board-power-entry>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Requirement]),
    [Mains connector], [IEC C14 (with integrated fuse) or regional equivalent],
    [Voltage range],
    [$qtyrange(100, 240, "VAC"), 50 "/" qty(60, "Hz")$ (universal) recommended. Factory setup accepted],

    [Safety], [Compliant with IEC 60950-1 or IEC 62368-1],
  ),
  caption: [Power entry requirements],
) <table-power-distribution-board-power-entry>

==== Master oscillator <power-distribution-board-master-oscillator>

To support the metrologic tier time-domain computations, the chassis must
include a precision clock source.

/ Oscillator: Oven Controlled Crystal Oscillator (OCXO).
  / Recommended part: AOCJY4A-10.0000MHZ-SW (or equivalent with
    $plus.minus qty(10, "ppb")$ stability).
/ Buffering: The oscillator output must be filtered to remove harmonics and
  buffered to drive the $qty(50, "ohm")$ distribution network.
  / Metrologic tier buffer: LM7171 (high speed, high voltage operational
    amplifier) or equivalent, configured to drive $qty(50, "ohm")$ loads with
    high slew rate and low distortion.
/ Signal level: $qty(1.0, "Vpp") plus.minus qty(10, "percent")$ into
  $qty(50, "ohm")$.
/ Waveform: Sine wave.
/ Fan-out: The oscillator distribution network must ensure port-to-port
  isolation $gt qty(40, "dB")$ to prevent oscillator line crosstalk between
  modules.

=== Front panel <chassis-front-panel>

The chassis front panel provides system-level controls and reference inputs and
outputs.

==== Elements <chassis-front-panel-elements>

#figure(
  table(
    columns: 3,
    table.header([Element], [Type], [Function]),
    [SAME logo], [Label], [N/A],
    [SAME license], [Label], [Legal],
    [Power switch], [Rocker or toggle], [Mains on/off],
    [Standby switch], [Toggle], [Maintains reference ovens temperature],
    [Power indicator], [LED], [Indicates power state],
    [Standby indicator], [LED], [Indicates standby state],
    [$plus qty(10.0000, "V")$ output jack], [4mm banana, yellow], [Reference voltage output],

    [$qty(-10.0000, "V")$ output jack], [4mm banana, blue], [Reference voltage output],

    [$plus qty(10.0000, "V")$ input jack], [4mm banana, white], [Reference voltage input],

    [$qty(-10.0000, "V")$ input jack], [4mm banana, white], [Reference voltage input],

    [AGND jack], [4mm banana, black], [Analog ground reference],
    [Dual $qty(10, "MHz")$ sine oscillator output jacks $plus.minus qty(1, "V")$],
    [4mm banana, light blue],
    [Master oscillator output (independent paths, to allow verification - see @the-time-invariant)],

    [$qty(10, "MHz")$ sine oscillator input jack], [4mm banana, white], [Master oscillator input],

    [Calibration coarse], [Rotary or DIP switch], [Reference voltage coarse adjust],

    [Calibration fine], [Rotary or DIP switch], [Reference voltage fine adjust],
  ),
  caption: [Chassis front panel elements],
) <table-chassis-front-panel-elements>

- Case designers may add other elements as they see fit (fuse holders, voltage
  selectors, sensors, etc.),
- Reference jacks should be grouped together, on a $qty(0.75, "inch")$ grid,
- All controls and jacks must have an associated label.

=== Electrical safety <chassis-electrical-safety>

==== Mains isolation <chassis-mains-isolation>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Requirement]),
    [Isolation voltage], [$gt.eq qty(3000, "VAC")$ mains to SELV],
    [Creepage / Clearance], [Per IEC 60950-1 or IEC 62368-1],
    [Fusing], [Primary slide, appropriately rated],
    [Earth bonding], [Continuous, $lt qty(0.1, "ohm")$ to mains earth],
  ),
  caption: [Mains isolation requirements],
) <table-chassis-mains-isolation>

==== SELV circuits <selv-circuits>

All module-facing voltages ($plus.minus qty(15, "V")$, $plus.minus qty(10, "V")$, $plus.minus qty(5, "V")$) are Safety Extra-Low Voltage (SELV):

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Requirement]),
    [Maximum voltage], [$lt qty(60, "VDC")$],
    [Isolation from mains], [Required],
    [User accessible], [Yes (banana jacks)],
  ),
  caption: [SELV circuits requirements],
) <table-selv-circuits>

==== Protective earth <protective-earth>

#figure(
  table(
    columns: 2,
    table.header([Parameter], [Requirement]),
    [Earth continuity], [$lt qty(0.1, "ohm")$ from any exposed metal to mains earth],

    [Earth current capacity], [Per fuse rating],
    [Chassis bonding], [All panels bond],
  ),
  caption: [Protective earth requirements],
) <table-protective-earth>

=== Compliance <chassis-compliance>

Chassis must comply with applicable safety and EMS standards for the target
market:

#figure(
  table(
    columns: 3,
    table.header([Region], [Safety], [EMC]),
    [EU], [IEC 62368-1], [EN 55032, EN 55035],
    [USA], [UL 62368-1], [FCC Part 15],
    [International], [IEC 62368-1], [CISPR 32, CISPR 35],
  ),
  caption: [Chassis compliance requirements],
) <table-chassis-compliance>

Compliance testing and certification are the responsibility of the chassis
manufacturer.
