Unfortunately, there is no leakage specification publicly available for such SWITCH cards.
Are you looking for the isolation resistance of the relay contacts or channel-channel leakage or channel-Gnd leakage?
In any case, I believe to get such data you would have to reach out to NI Support.
Each of the 10 channels on the board have two terminals, comX and chX.
I am after the leakage resistance with comX and chX open.
I believe that corresponds with the channel-channel resistance you indicated.
Okay, that would mean it is relay contact isolation resistance. It should be fairly in the Giga ohm region given this is an electromechanical relay.
As per this link, Tyco relays are used in the instrument
Looking at the relay datasheet, there is no specification about the leakage through the air-gap between the contacts but they do mention that the dielectric strength is 1000Vrms between open contacts.
Channel to Channel resistance is between CHx and CHy or COMx and COMy
Given these are electromechanical, you will get the best leakage (least) between the COM and CH, why would like to know the exact value? are you trying to measure in pico amps?
Thank you for asking!
According to my calculations, the leakage resistance is on the order of 180 kOhms to correct my readings against expected readings.
As to the current, the leakage current is roughly 0.14 milli-amps
180kOhm between COM and CH does not sound right in an open state for an electromechanical relay.
If what you say is true, the relay could not claim to have a 1000Vrms isolation.
Could you please explain the method you used to measure or come up with this 180kohm measurement?
Measurements were performed using an MDO4104C scope.
Channel 1 measures the peak to peak amplitude of a sinudoid (28.0477 Volts)
The signal passes through an 8.25 kOhm resistor where
Channel 2 measures the peak to peak amplitude as 26.943 Volts.
Theoretically, these two Voltages should have been the same!
The signal then passes through a 16.9 kOhm resistor, and then
through an open channel on the PXI-2586 board.
The common side of the open channel is tied to return, completing the circuit.
If the open channel is a leakage resistance of ~180 kOhms, then the Voltage divider equation works!
That would not be the right way to measure the isolation resistance. Isolation resistance is a DC parameter and not measured with an AC stimulus.
Could you please draw up a simple circuit of the connections? and what is the frequency of the 28V AC signal?
Since you're talking about AC signals, we do have specifications on isolation.
I would simplify the test circuit as below, the numbers in dB are x-y
For example, if you apply a 1Vrms 1MHz signal at CH, then you would measure <= 3.16mVrms at COM terminal which translates to 50dB.
If your source impedance of the signal is high enough, then this will act as a voltage divider and will attenuate your signal.
I was describing the parameter as leakage resistance - intending that this is the resistance across a pair of open relay contacts. If the correct term is isolation, so be it. Sometimes isolation can also be associated with a channel to channel measurement - which I want to avoid. Here is a schematic defining what I am testing:
Sw is placed to indicate the open relay contacts.