Input from SSR

[Dan R]

Hi,

I am having problems getting a signal from an SSR.  It has an internal resistance somewhere between 40 and 100 ohms (nominally about 50 ohms).  The SSR has normally open and normally closed contacts and I need to check that both sets of contacts are functioning when expected to.  I have connected the common line of the SSR to ground and the N/O and N/C lines to two digital inputs of PCI MIO -16E - 4.  The N/O input seems to function as expected, but the N/C line is pulled high (positive input) when not connected, and the relay passes the test.

What options do I have for connecting the relay as an input to the DAQ board?

Thanks,

Dan

[Tom.]

Hello Dan,

Can you provide information on the SSR please? Also is the common pin you mentioned connected to the GND of the board or another grounding source? It would be beneficial if you can provide a wiring diagram of your setup.

Cheers

Tom | NIUK

[Dan R]

Hi Tom,

The COM line is connected to the ground of the board, but htis is also connected to the ground of the power supply.  To be honest, I didn't think it would work unless I did that. 

Hopefully the attached diagram will be of some use.

FS2 and FS3 are fuses and VDR4/5/6 are transient suppressors. 

I'm afraid I don't know much about these, but it doesn't look like they should affect my test.

Thanks,

Dan

[Dan R]

Here is the datasheet for the relay.

[Tom.]

Hello,

Does removing the elements labelled 'VDR' change the way the signals are read? To pull the line you are talking about to 0V it must have a path to ground (usually through a resistor) but at the moment im not sure whether the 'VDR' elements are prohibiting that. Is the line you are writing to an Analogue Input or Digital Input?

Tom  | NIUK

[AnalogKid2DigitalMan]

en8dsr:

The data sheet you posted is for a Form A contact (normally open) configuration. A relay that has a normally open and closed contact set is a Form C. You simply have two normally open contacts in you device that are under independant control.