Automating Repetitive Hardware Design: Building a 36-Channel High-Voltage Test Rig

A test engineer at a cable assembly manufacturer wants to automate insulation measurements across a 36-conductor cable. The bench setup relies on moving probes and recording results by hand, so the fixture needs a 36-channel switching matrix and a guarded rack frame.

The manual sequence required repeated probe changes and handwritten records. A probe could slip and force the technician to repeat readings, so the test engineer proposed a switching fixture with one position for each conductor on the high side and one on the return side. That meant 72 switching positions, a test board, and a rack fixture for a production bench.

Make the switching matrix visible before routing

The test engineer wrote down the test interface, the 36-wire connector map, the production test threshold, and the required record for each pair. The control system could select one wire from each group, run the approved measurement sequence, and return a result to the technician's computer over USB. The high-voltage path had to remain physically separated from the low-voltage controller.

The proposed six-layer board measured 196 by 132 millimeters. Its 72 switching positions used CPC1972 PhotoMOS relays, arranged as two labeled banks of 36. A low-voltage controller managed the selection lines. Guarded terminal blocks connected the cable fixture, and a USB interface carried the result record. The test engineer divided the board into an isolated switching region, a control region, and a service edge.

She entered the cable pin map and required spacing in the project before asking for a layout. The Flux agent built the schematic and routed the board around the 72-device array. The test engineer reviewed the CPC1972 datasheets, package orientation, and switching path. She made sure that every device number in the layout matched the test matrix table, then ran design rule checks on the board.

The review exposed two practical details. A row of test points would be hidden under the top cover, and a control connector faced the wrong side of the rack. The test engineer moved the test points to the service edge and rotated the controller header. She checked the isolation boundaries and creepage paths against the company's approved test design before approving the routing.

A rack fixture had to protect the operator and the wiring

The first sketch showed only a board and a cable. The test engineer brought the fixture lead into the review because the production team needed strain relief, a clear interlock, and room to replace the cable adapter. The mechanical engineer imported the existing 19-inch rack outline and measured the bench's cable approach. The new frame used 2-millimeter grounded steel panels with a removable top cover.

Inside the rack, an insulating barrier separated the switching board from the 24 V control section. The front panel held two keyed cable receptacles, a guarded status lamp, and a latching test control. A hinged service cover exposed the low-voltage USB port and board status LEDs. The mechanical engineer added a cable clamp and a removable adapter plate so the fixture could accept the two connector shells used by the cable line.

The switching board sat on four 8-millimeter standoffs. The mechanical engineer used the 3D view and X-ray to inspect the board beneath the cover, then checked the insulating barriers and cable bends. The first frame layout placed a steel lip too close to a guarded terminal. He shifted the lip 6 millimeters and extended the barrier to cover the full connector edge. The cover interlock opened before an operator could reach the switching region.

They also reviewed heat and service access. The low-voltage controller and relay array sat on separate zones of the board. A thermal simulation showed the controller area stayed within the component limits during the expected test cycle. The mechanical engineer kept ventilation slots above the control supply while leaving the high-voltage partition closed. The board could slide out from the rear after removing four captive screws, without disturbing the front cable adapters.

The requests the test engineer used to shape the rig

Build a 36-conductor insulation test matrix for the manufacturer's cable line. Select one conductor from each side of the test pair, record each approved measurement, and keep the operator away from the switching region.

Arrange 72 CPC1972 switching positions as two banks of 36 on the 196 by 132 millimeter board. Keep the high-voltage paths separated from USB and 24 V controls, preserve the cable map, and show creepage boundaries for review.

Design the rack frame around the existing 19-inch outline. Add a closed high-voltage compartment, removable adapter plate, cable clamp, guarded controls, and rear board access; check the cover and barriers against the board in X-ray view.

One test no longer meant a long row of probe moves

The test engineer and mechanical engineer completed the board and frame review in an afternoon. They inspected the switch array, connectors, service points, and cover interlock in the same project. Circuit simulation covered the controller supply and switching control. The manufacturing package included the Gerbers, BOM, pick-and-place data, wiring map, and STEP assembly.

The assembled fixture used the 196 by 132 millimeter six-layer board, 72 CPC1972 devices, controller, USB interface, and guarded connectors. Its mechanical design included the grounded steel rack, internal insulating barrier, cable clamp, removable adapter plate, captive cover, and service panel. The test engineer could load a cable, close the cover, start the approved sequence, and receive a recorded set of measurements.

With the fixture, the test sequence no longer required manual probe moves. The test engineer reviewed its records against the approved procedure. The operator could load a cable, close the cover, start the sequence, and receive a recorded set of measurements.

The design also made the fixture easier to maintain. Each conductor had a labeled path from the front adapter to its switch position. The mechanical engineer kept the cable clamp and adapter plate replaceable, so a worn connector would not require rebuilding the rack. The test engineer added the test map and approved spacing review to the manufacturing package before the fixture entered the line.

A checklist for a repetitive test fixture

• Write the conductor map, measurement sequence, and approved test limits.
• Separate switching, control, service, and operator interfaces on the board.
• Review device count, package orientation, spacing, and design rule results.
• Model the rack, barriers, interlock, cable clamp, adapters, and service access.
• Check the complete board under its cover with X-ray and relevant simulation.
• Document the fixture wiring and export board, BOM, assembly, and STEP files together.

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