I've been needing to measure the insulation leakage current for an electrical connector.
I've rigged up a little insulation test setup with a HP 3457A, a Fluke 415B power supply, a 100k ohm resistor, and a safety crowbar gas discharge tube. I'm getting voltages in the 1uV - 30mV range across the resistor (~300GOhm - 1GOhm), more typically 5uV - 50uV. Test voltage is 30V - 500V, surviving 1000V would be nice.
I'd like to make an 8 channel relay scanner card so I can do all the combination of pins in the connector. Maybe first by throwing some DIP switches, later by fully automating w/ GPIB, the input scanner card on the 3457a, and some GPIO to control the relays. I want to be able to apply voltage to and measure current out of any combination of pins, I'll probably have 16 SPST relays.
Do I need anything special for the relays? Like low EMF? The signal is down in the uV range, but since the sense resistor is local and not going through the relay so I don't know if it matters.
I was considering these ones, high voltage rated reed relays. The relays are not directly switching the full voltage since the DUT is between them, but in case of a burn-through I was looking for relays that could handle the full voltage.
Reed:
- Meder SHV05-1A85-78D4K
- Meder LI05-1A85
- Pickering 100-1-A-5/2D
LI05-1A85 looks nice because it has very low leakage, 10Tohm. I'm leaning towards this one, although it is not low emf and is not shielded.
It doesn't need to switch super fast, doing 5 samples per test point at 100 PLC, so maybe will switch every 5s-10s. i'd like to be able to switch at a few Hz.
- Should I use a reed relay? Which do you like for 1000V 0A?
- Should I get a special low EMF relay? Does thermocouple effects matter?
- Should I use a more normal mechanical relay? Maybe latching? Favorites?
Circuit sketch attached. The TP are the pins of the connector, so the sketch is measuring the resistance of pin 1 to pin 2.