WebDAQ 504 digital input wiring

[Tobias Z]

Hi,

i couldn't find any diagrams which shows the possible wiring on the digital inputs of the WebDAQ 504.

Can someone please provide me with some information for the wiring?

Thanks

[JRys]

Hello,

The WebDAQ digital input is internally pulled up to +5v via a 100k ohm resistor. Assuming the relays is the dry contact type, it can only pull the digital input down to ground (GND) when it closes. When open, the input will return to +5v.  I'm sorry, but it doesn't provide a means to change the internal pull up to pull down and because of this, I don't see a way of reading a logic low with the relay contacts open. However, if you're looking to trigger the WebDAQ 504 when the relay is open, use rising edge as the type. This will force it to wait for the input to transition from low to high or from closed to open.

Best regards,

John

[Fausto]

Hello @Tobias Z.

There is no digital I/O diagram in the WebDAQ 504 User's Guide.  However, the bottom of page 10 shows a figure of the digital I/O screw terminal pinout.  The top of page 11 describes the digital I/O lines.  Via software, each bit is individually configurable as an input or output.

https://www.mccdaq.com/pdfs/manuals/WebDAQ-504.pdf

Are you configuring the digital I/O lines as inputs only?

What type of signal will you be connecting to the digital I/O lines?

Regards,

Fausto

 

[Tobias Z]

Hello @Fausto

We are using the DIO lines only as input and connecting relay contacts to the I/O lines.
Is this configuration possible?

Similar like this:

Kind Regards

Tobias

 

[Fausto]

Hello @Tobias Z.

Please compare your signal voltage levels with the WebDAQ's digital input specifications on page 24 of the user's guide.  

https://www.mccdaq.com/pdfs/manuals/WebDAQ-504.pdf

Signal levels to the digital input pins should be between 0-5 V.

Regards,

Fausto

[Tobias Z]

Hello @Fausto

so if we connect to the relay contact a 5VDC source this should work?

Kind Regards

Tobias

[Fausto]

Just to confirm that you are not controlling the relay with the WebDAQ, but instead, reading an output level between 0-5 VDC, from the relay to the WebDAQ's digital input pins.  If this is correct, then it should work.

[Tobias Z]

Hello @Fausto

thank you for the fast response, yes we want to read 0-5 VDC on the input pins of the WebDAQ.

[Tobias Z]

Hello @Fausto

I connected the relay contacts to the DIO 0 on the WebDAQ 504, but I only get a 5V (High) reading.
On the REST API Help (https://www.mccdaq.com/downloads/WebDAQ/REST-API/1.0.0/webdaq-rest-api.html#digital-information-digital-bit-get) it reads:

Quote

Bits intended to be used as input should be left at the power-up default value of 1.

But this results in a value of 1 (5V) when the relay contact is open or closed.
How can I get a 0V reading when the relay contact is open?

 

Kind Regards

Tobias