Physical Connection of a half bridge Strain Gauge in a NI 9237

[javihn]

Hi everyone,

Im using the NI 9237 module to make some strain gauges measurements. I have a Rosette Gauge and a NI 9947. I'm trying to do a Half Bridge configuration. I haven't being able to do the measurements because I don't know how to make the physical connection of the Rosette Gauge wires to the NI 9947. I do know that the NI 9237 have 2 inner resistors. I have a little program already done, but I'm stuck in the connection part to start testing. Could someone tell me how to connect the gauge wires to the NI 9947 and if resistors are needed, how are they also connected to the NI 9947.

Please Help Me!

Javier Vijil ( jvijil@empire.hn )

[Cavarval]

Hello Javier,

You mean NI 9949?

From your picture I could not judge whether the strain gauges are really half-bridge (two active elements per pair of wires). If you are certain it is, just refer to this under Half Bridge. The pins on the NI 9237 match the pins on the NI 9949, so you should be able to get the connections done just as shown in the picture. The green wires are optional and are typically used in half or full bridge configurations, mainly  when the leads are long.

If each pair of wires is connected to a single active element, it should actually be treated as a quarter bridge, in which case you can do this or replace the NI 9949s with NI 9944s or NI 9945s depending on the gauges nominal resistance, as shown in the first link.

Essentially, each pair of wires would be one channel, so you need to connect each one to the gauges from the rosette to one channel from the NI 9237. Refer to the Strain (Rosette) - SW-Timed Input.vi example in the example finder in LabVIEW by going to Help»Find Examples... and browsing (according to task) to Hardware Input and Output»DAQmx»Analog Input.

The example will not work right away with the NI 9237 because it does not support software timing so you will need to add the sample clock just like in the vi from your other post. The example uses three channels in the default configuration for a Rectangular Rosette like yours.

Please take a look at the info and let us know if you have further questions.

Regards,

[javihn]

Hi Camilo,

Your info. is very helpful, Thanks a lot.

I just look up the example of the Strain Rosette Measurment and I added my Sample Clock as you suggested. But, Still the same error when running. What I see is that I need to add 2 more Physical Channels in the Block Diagram, but the question would be, How should those physical channels be connected to the AI Rosette Strain Gage Block? Because it only allows me to connect 1 physical channel.

[Cavarval]

Hello,

Check this out. 

Either of the two LabVIEW options should work for you.

Regards,

[javihn]

Thanks for the data Camilo,

I already have the Physical Channels configured and they show me the list of channels that I can Use. But still, how do I make the assignment of physical channels to the program in the Front Panel if it only allows me to choose 1 and it does not saves them in the channels list. How can I choose the other 2 channels that are still missing so the program can work.

Regards,

[Cavarval · Accepted solution]

Hello,

The last article I linked shows how to do it in the block diagram, but you can do the same thing in the front panel. You can expand the drop down menu from the Physical Channels control, select Browse and use the shift key to select multiple channels, or you can enter them manually using a colon if they are consecutive channels. The next link will also be useful.

http://zone.ni.com/reference/en-XX/help/370466V-01/mxcncpts/physchannames/

In the end, if you want to use channels 0, 1 and 2, the control value needs to be Dev1/ai0:2, just like in the LabVIEW example (as long as Dev1 is the NI 9237's name in NI MAX, but it will probably be something like cDAQ3Mod1/ai0:2).

Regards,

[javihn]

Hi Camilo,

You are the best of the bests. Thanks a lot. The program is running fine. The only detail that I still have to do is to show the values from the DAQmx to a waveform graph. Your help was very useful.

Regards

[Cavarval]

Glad to help! 

Let us know if you get into trouble with the display and we'll try to help!

Regards,