What NI module to read Full Bridge with up to +/-60 mV/V input range

[ngthai]

I have full bridge Pressure Tranceducers with Full Scale Sensitivity up to +60 mV/V

I used NI9237, but it reads only to +/-25mV/V thus, with excitation of 5V the signal will max out at 125mV (Pressure 50psi) whereas I would like to increase Pressure up to Full Scale (100 psi).

Is there an NI module that gives me up to +/-60 mV/V for Full Bridge instrumentation?

Thank you

[_kb]

Hi ngthai,

Check out the Universal AI module, NI 9219.  It meets your input range requirement, but you should look over the rest of the specs to be sure it's suitable for your application.  If you'd like to discuss with one of our engineers, give us a call at (888) 280-7645.

[ngthai]

Thank you.

My next question is: In Labview, if I use 10V excitation then the NI9237 would give me same mV signal output when I checked using Multimeter.

However, if I use 2.5V excitation, NI9237 gives me only 1/4 of the mV that I would read from Multimeter. So I have to use the scaling like this:

My general question is:

Is this correct: Raw Full Scale (Enable Scaling) = 10 V / Actual Excitation Voltage * 10 ?

(so if Excitation is 3.3, then Scale = 10/ 3.3 * 10 = 30.3

if Excitation is 5, then Scale = 10/5 * 10 = 20)

?

Thank you

[_kb]

I'm not sure what you mean.  What are you checking with a multimeter?

The sensors that you use should call for a specific excitation voltage, so I don't know why you would use different excitation levels.  The data sheet for the sensor should also have information on sensitivity / scaling, to help with the conversion from mV/V to pressure units.

[ngthai]

I have 2 sensors from 2 vendors.

* sensor A, the vendor provides calibration sheet which shows 5V Supply. 

* sensor B, the vendor provides calibration sheet which shows 10V Supply.

As sensor A is designed for 5V, when I plug A and B both in NI9237, I dont want to use 10V. I used 5V for both, since they are on 1 NI module.

I understand about scaling the mV output to psi pressure. I need to use a factor of 2 for Sensor B, and factor of 1 for sensor A. I don't have any question regarding that.

My question is related to the readout in mV itself. I found out that on both sensors, if I don't use "Enable Scaling" my Labview Project ScanIO-Chassis Deployment, then the readout in mV would not be the same as when I double-checked using multimeter.

I double-checked using multimeter by measing the voltage out from pins #2 and #3.

My question is related to the Labview Project ScanIO-Chassis Deployment which relates to Raw Full Scale (in the previous picture) regardless of what sensor I have: Is this correct: Raw Full Scale (Enable Scaling) = 10 V / Actual Excitation Voltage * 10 ?

Thank you.

[_kb]

For ratiometric (bridge) measurement devices like the 9237, the raw measurement is a mV/V reading that compares inherently the output of the sensor to the excitation provided, so you wouldn't be able to verify directly with a multimeter across the AI pins.  What is your objective?

[Henrik_Volkers]

A resitive bridge is ratiometric and it's sensitivity is noted in the spec as mV/V, so it doesn't matter if you supply them with 5V or 10V.

However some PIEZOresitive  bridges are not fully ratiometric and the vendor specifies the valid exitation voltage (range), just check your sensor datasheets (and call the support number usually also noted on the datasheet if you are not shure about it).