How to use external excitation with the 9237

[CRB]

OK, I just checked it using Signal Express LE.  I get the same result.
When I ask for 10 V internal, the actual is 8 volts.
When I switch to external source, I get 7.6 volts, regardless of what my external power supply does.

One last question about hook up.  The four terminal plug that is used for input of the external source power has two connections for EX+ and two for EX-.  I am using the top set of connections.
I assume that the two EX+ connections are wired together internally.  Is that correct?
Ie, it should not matter which of the two sets of EX+ and EX- I use.

[Frank-L]

You are correct in that it should not matter which of the two sets of excitation pins you connect so long as it is connected correctly. The reason behind the two sets of excitation pins is to perform daisy chaining of the 9237. I am confused as what you mean by top set of connections, as the top two should be for positive terminal of the excitation source, while the bottom two are for the negative terminal of the excitation source (Page 6 of 9237 User Manual). Attached below is an image of how to daisy chain multiple NI 9237 devices as well as providing a easy to identify image of how to connect the device correctly. 

[CRB]

Thanks

I have it set up correctly.

I have the device laying flat, so the "top" includes a EX+ and EX-.

Should I consider sending this particular device back to you to see if you can find a problem with it?

[CRB]

So, I did send in my original device for repair/investigation.

Today I got back a refurbished replacement (different serial number).

I tried it out.

It behaves exactly the same way, paying no attention to the external excitation voltage I input.

Do any of the 9237 devices work as we would expect?  or I am doing something wrong that we have not figured out yet....

CR

[Frank-L]

The NI 9237 devices should work as expected as detailed within the information that I have provided. I went ahead and did a test of this setup myself with a 350 Ohm load cell, a NI 9237, and one of our DC Power power supplies. When selecting solely internal excitation, I was able to achieve around 7.9 V as you did. After passing the voltage in through the external connector on the front of the NI 9237, whether specifying internal or external excitation, the voltage going to pins 6 and 7 on the RJ50 cables were forced to be 10 V as measured by a DMM. Perhaps the NI 9942 4 pin external power supply connector is not hooked up correctly and not actually connecting the power supply to the excitation pins. 

[CRB]

This is in fact the problem.  The Molex connector pins did not extend far enough to contact the pins internal to the NI9237 external supply.  I bypassed the Molex connector and attached directly to pins internal to the NI9237 and all worked as expected. I will try to get the Molex connector working as intended.  Screw terminals would have been my preferred connection method.

Thanks for all your help ruling out other possible problems. 

[motormannie]

Can anyone help with a source for the  for the external power supply connector?

I wish it was a screw block arrangement, you could still daisy chain, and ensure decent connection...

[Brian_P]

motormannie,

Thank you for using the forums.  Are you using the RJ50 connector or the D-Sub Connector? With the D-Sub Connector we do sell a screw terminal block for the 9237.  That connector can be found here.  The connector is called NI CB-37F-LP.  It can be found under the accessories on the page I had mentioned.  As for the RJ50 connector, we don't actually have any screw terminals for the actual excitation part.  I apologize if this is an inconvience.

Regards,

Brian P.

[motormannie]

Hi

It's the RJ50 model, i'm just after the connector that i can then solder onto or connect somehow.

At the moment, because i cant connect to it, i cant use all 4 channels at 10V excitation...

Any help for a supplier for this connector would be useful.

I think it's a bit silly that we cant source a connector from NI? or am i wrong?

[Brian_P]

motormannie,

Thanks for your reply.  The connector for the 9237 external excitation source can be found here.  Please let me know if this is what you are after.

Regards,

Brian P.