In my system I want to measure multiple DC voltages with a single multimeter. I'm thinking of using relays to switch between the different signals.
But relays specifications tend to indicate, that I actually can't use them for this purpose.
One of my signals is from a high precision current shunt (Vishay HZ series) with an expected signal range of 550 mV to around 4.3 V. The others are in the range of 0 to 10 V.
I'm not too concerned with the switching capacity of the relays. It's used in a production equipment and can be replaced on a regular basis; I expect around 20000 switch overs per year.
Solid State Relay
Solid state relays usually have a minimal output voltage specification, which is higher than 550 mV. So it can't be used for the current shunt and for the 0 to 3 V range of the signals.
Furthermore, they typically have leakage current specification which would defeat the whole purpose of the high precision current shunt (leakage > 1 µA).
Standard electromechanical relay
The problem with standard electromechanical relays is the requirement of minimal load current. To get anywhere near the load of a voltmeter (1 µA at 10 V, or even less if switched to >10 M\$\Omega\$) I need gold-plated contacts.
But even gold-plated contacts are rated for a minimal load current in the order of 1 mA at 24 V.
In most of the datasheets I haven't found a mention of a minimal required load current or voltage specification.
I'm not sure if that means that it doesn't matter (because of the sealed enclosure there is no oxide build up?), or that the manufacturers don't care.
Currently I'm leaning towards reed relays, but I'm not sure if I'm missing something.