NI-9482 leaks AC when the relay is in the open position.

[RayH2025]

Hi, I am trying to use the NI-9482 relay module to open and close a circuit with a 32 kHz square wave (1.6 Vpp amplitude). I am applying the signal to CH0a. When the relay is in the open position, I am expecting minimal leakage on CH0b. However, CH0b is showing over 1 Vpp. BTW, "relay in the open position" in this case means the relay module is not installed on the cDAQ chassis, so it is not getting any power (for controlling relay open/close). I measured the relay resistance in the open position with a DMM, and it shows OL (open circuit). All four channels are behaving the same. Did I purchase a bad part? Or am I doing something wrong here? Has anyone else encountered similar problems with leaking AC signals using this relay module? Thanks.

[santo_13]

Depending on traces and relay construction, it may be expected, you need to look for isolation specification when relay is open. Unfortunately, it is not listed in specification of 9482.

Found this image online, from the looks of the relay, the contacts must be close enough to capacitively couple signal when open (which you already figured out)

For example, PXIe 2520 relay card lists isolation and crosstalks specs.

Since Isolation for open channel is not spec'd, I assume this module is not for high frequency "signals", rather to switch loads AC (50/60Hz) or DC and at those very low frequencies the relay is truly open.

Typically, Omron G6K is widely used in the industry and here is the isolation spec for that,

If you have the means, you can characterize this isolation specification for 9482 or if you have NI technical support, you can request for that data.

[santo_13 · Accepted solution]

Additional thought, the brown capacitor like component next to the white relay on the 9482 seem like a varistor and that may be conducting at your frequency.

Here is a snippet from Vishay's varistor intro document that describes an example frequency response of a varistor,

[RayH2025]

Thanks, Santo. I think you are correct that this relay module is meant for switching DC or AC loads (at 50/60 Hz). It is not ideal, but I am going to add a relay circuit and use a DIO module for control instead. Again, I appreciate your help.

[BertMcMahan]

You may be able to work around this depending on how many channels you have. If you only need to switch one or two channels, you could use the other two channels on the relay card to ground the "floating" channels (basically turning it into 2x DPST relays).

Alternatively, you can just chain a separate relay with better isolation, and use the 9482 to drive the second relay. That way you don't have to buy a second DIO module.