Problem
Our customer asked us to create a device to calibrate production line test equipment. The instrument must have the shape of the ink cartridge that was being produced on the line. The circuit was an adaptation of an earlier calibration pen we had made for this customer.
Solution
We used the components from a Tektronix clip-on current probe and installed them on the circuit board in the cal pen. There were numerous circuits to test so we used mil-spec mercury wetted relays to multiplex the test circuits into a single set of signals.
A cable carried these signals and the control signals for the multiplexing circuit from the cal pen to a VXI Bus board. We used a stock VXI prototype card for the bus interface and "piggybacked" onto it a pen controller circuit board that we designed.
The calibration circuit was housed in a machined metal pen body. The contact pad array had gold-plated terminals press fit into a machined Delrin spacer, with the terminals soldered into a connector PCB. The high precision load resistors were installed on a separate plug-in circuit board to allow resistors with different values to be installed.
Results
The calibration pens allowed very precise adjustment of the production line test circuits, resulting in reduced waste in the manufacturing process.
