INA114: Strain gage measurement using INA114BP

Dinesh Kumar14

Part Number: INA114

Hello everyone,

We are trying to measure the output voltage of the Strain Guage using he INA114 precision Amplifier. The strain Guage is connected in the form of Wheastone bridge wih 330 ohm resistors (Strain Guage Rg = 350 ohms) and excitation voltage for Strain Guage is in bipolar (+- 5 volts) and (+-12 volts to Amplifier IC. The voltage across the wheatstone bridge is given as a signal input to the amplifier IC. The signal voltage is 0 volts in the sable condition and as we are compressing the strain guage the output voltage of amplifier should vary from (0 to 10)volts, But the amplifier output which we are witnessing on the mulimeter is varying from (+11 to -11) volts and it does not remain stable a the particular resistance value.

So we are not able to figure out the problem here, Its our assumption that may be the gain of he amplifier IC is creaing that issue. It would be great if we could get to know the exact problem and the solution for this issue.

Thanks

Dinesh S

over 5 years ago

0 kai klaas69 over 5 years ago

Guru 140200 points

Hi Dinesh,

have you connected the REF pin properly? Is the gain set too high?

Can you show us a schematic?

Kai

0 Dinesh Kumar14 over 5 years ago in reply to kai klaas69

Prodigy 20 points

Hello Sir,

I would like to thank you for your reply. Actually Sir as we have a custom made PCB for the signal amplification of the sensor and unfortunely we do not have any schemaic file for the amplifier PCB. As far as we know and as we have checked the PCB the Rg is 1000 ohm on the PCB board and according to the datasheet the desired gain is set to around 50 for the INA114 IC on the PCB.

Since we are unaware of the most of the things for this IC nd also about the gain and as we are new to these, Below are the values we tried check wih the mulimeter the values are mentioned below these are with respect to the common.

V+ = 12 volt
V0 = 0.7 volt
V- = - 12 volt
Vin+ = 0 volt
Vin- = 0 volt
Vref = 0 volt

It would be great if you could help us by giving any approach for solving this problem.

Thanks
Dinesh

0 Tim Green1 over 5 years ago in reply to Dinesh Kumar14

TI__Expert 6275 points

Consider looking at the following training on op amps that is also applicable in most areas for Instrumentation Amplifiers.
training.ti.com/ti-precision-labs-op-amps
Consider also downloading and using the Instrumentation Amplifier Common Mode Voltage calculator to see where you can operate the INA114 in the linear region.
www.ti.com/.../INA-CMV-CALC

0 Dennis Goeke over 5 years ago in reply to Tim Green1

TI__Genius 11135 points

Dinesh

We haven't heard back from you so we assume you were able to resolve your issue. If not just post another reply below.

Thanks
Dennis

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INA114: Strain gage measurement using INA114BP