NI-9237 connection

[realbasil]

I have 4 full bridge load cells  which have the following specifications.

Output resistance – 350 ohms. Excitation voltage- 10Vdc. Ranges- 3K, 2K, 5k, 10K lb.

The internal excitation voltage that NI 9237 provides have a limiting power of 150mW for 350 ohms. My understanding is this will reduce the output excitation voltage for my loadcell (7.24 V), and it will reduce the excitation voltage further when I connect the remaining 3 load cells. This can cause error in my readings. Am I correct?

If that is the case, I would like to give 10V external power supply to the NI 9237. If I do that what would be my power input requirement? I am thinking of using a voltage drop across 24 V supply down to 10 V. Other than maintaining the voltage to 10 V supply to the external excitation line, do the 9237 Module have any power restrictions (like 150mW power restrictions for internal excitation voltage) for external excitation?.

[GerdW]

Hi basil,

what's wrong with using an excitation of 3.3V as written in the datasheet?

---

@realbasil wrote:

I have 4 full bridge load cells  which have the following specifications.

Output resistance – 350 ohms. Excitation voltage- 10Vdc. Ranges- 3K, 2K, 5k, 10K lb.

---

This "excitation 10Vdc" rating surely is a max value, so why go the way of adding external components to your setup?

Why do you think using a "voltage drop down to 10V" (aka resistor) from a 24V supply will make this approach more capable?

[realbasil]

"This "excitation 10Vdc" rating surely is a max value, so why go the way of adding external components to your setup?"

Greg, From the calibration data , 10 V excitation voltage is provided for these load cells. The output of the load cells are in mv/volt. So my understanding is that we have to provide 10 V all the time. Am I correct?. If not, I am happy to use 3.3 V internal excitation voltage. 

[GerdW · Accepted solution]

Hi Basil,

---

@realbasil wrote:

Greg, From the calibration data , 10 V excitation voltage is provided for these load cells. The output of the load cells are in mv/volt. So my understanding is that we have to provide 10 V all the time. Am I correct?.

---

Who is "Greg"?

Why do you think you need to supply exactly 10V for excitation? Who says so?

Apart from calibration sheet: what does the datasheet of your sensor say about excitation voltage range?

You can use any excitation voltage (within allowed range), this will not change sensitivity! You get 2.233mV/V for 10V as well as for 3.3V excitation!

Only difference is given in the NI9237 datasheet, see the specs for offset drift, noise, etc.

[realbasil]

Gerd I meant. Sorry. 

Thanks for being the professor for me.

The data sheet says the excitation voltage to be 10 V with a max of 15 V.

So if I understand this correctly, 3.1 V excitation voltage still gives the full range, although compromising the resolution. 

[GerdW]

Hi Basil,

---

@realbasil wrote:

So if I understand this correctly, 3.1 V excitation voltage still gives the full range, although compromising the resolution. 

---

The resolution will stay the same no matter which excitation voltage you use: it is specified in the datasheet as "24 bits"…

The offset drift and noise is given in the datasheet as dependent from excitation voltage…

(You probably talk about accuracy.)

Conclusion: when talking about sensors and measurements you should use correct wording! Don't you learn that at high school/university/apprenticeship?