PCIe-6343 + SCB-68A with Phoenix Contact OPT relay - do I need pull-down?

[RTSol]

Hi All,

I'm using PCIe-6343 card and SCB-68A connector block to turn on and off some opto relays from time to time 🙂

The issue is, that after I'm turning my PC off, relay diode constantly light up a little..

There is an information that 50kOhm pull down resistor can be used with 6343 card in manual, but SCB connector block manual contain no information about that.

Thats why I would like to ask more experienced users (or just someone with electronic knowledge) - should pull-down resistor solve my problem?

If yes - any guide how to install it in SCB-68A connector block?

[TSE_Expert]

Dear RTSol,

The PCIe-6343 Digital Outputs will be floating after switching the power supply off. So if the power supply is off, and the LED in the relay still lights a bit, the current is coming from the external circuitry. After the Reset of the 6343, i.e. after the return of the supply voltage, the hardware sets all DIO lines to high impedance inputs. The internal 4.7 kOhm pull-up resistors will pull the pins anyhow up in the direction of the bus-voltage, which could explain 0.6-0.7 mA current through your LED also depending again on your external circuitry.

http://www.ni.com/documentation/en/multifunction-io-device/latest/usb-6343/overview/

Try the minimal allowed 20 kOhm pull-down resistor to sink some current, it might help.

Best Regards,

NI Applications Engineering