How to connect a strain gauge and external resistor to the NI-9949 (Quarter-Bridge Configuration)

[JACK-5]

Hello,

I’m working on connecting a strain gauge to the NI‑9949 module, which is interfaced with an NI‑9237. From what I understand, this setup uses a Wheatstone bridge configuration. I’m planning to use a quarter-bridge setup, and I’ve seen that an external precision resistor is required to complete the bridge.

I found some documentation and wiring diagrams explaining how the pins on the NI‑9949 are supposed to be connected, but I’m still unsure how to apply this to my setup in practice.

I would really appreciate your help with the following questions:

1. Which pins from the NI‑9949 should be connected to the strain gauge?

2. Which pins should be connected to the external precision resistor?

3. What kind of external resistor should I purchase (resistance, tolerance, power rating, resistor type)?

I’ve attached the following for reference:

• Photo of the NI‑9949 module

• Photo of the strain gauge I plan to use

• Screenshot of the wiring diagram I’m following

• Datasheet for the strain gauge model

If it helps, I’m also open to sharing more details or photos of the physical devices I’m working with. Any guidance you can provide to make sure I’m wiring this correctly would be greatly appreciated.

Thanks in advance for your support!

[santo_13]

Since your strain gauge is 120 ohm typical, you need a 120 ohm precision temperature stable resistor for the quarter bridge completion circuit.

Or if you would like to keep it simple, get a NI-9944 to wire your strain gauge.

here is a resistor I found online - https://tacunasystems.com/products/hardware-accessories/strain-accessories/precision-bridge-resistor...

[JACK-5]

Hi Santhosh,

Thank you very much for your response — I really appreciate the link and your recommendation regarding the 120 Ω precision resistor. That definitely helps clarify the type of component I should look for.

However, if I may follow up, there are a couple of points from my original question that I’m still unsure about:

1. Which specific pins on the NI‑9949 should be connected to the strain gauge?

2. Which pins should be connected to the external resistor on the NI - 9949 to complete the quarter-bridge circuit?

I found a wiring diagram online (attached in the original post), but I’d really appreciate a confirmation or explanation to make sure I’m interpreting it correctly. It would help me feel more confident before moving forward with the wiring.

Thanks again for your support, and I look forward to any additional guidance you can share!

Best regards,

[santo_13]

You need to make the connections as shown above, all the three kind of wires (red, black and dotted). Replace R4 with your strain gauge and R3 with your 120 ohm precision resistor.