Help me designing instrumentation amplifier for pressure sensor

[Prasanna hegde]

Hello all,

I am using a pressure sensor which gives Vout+ and Vout- as output. ( its a 4 resistor bridge type). It is 0-500psi sensor and output is 10mV/V(vcc)
We have supply voltage of 3.6V
Reference voltage to amplifier is 2.5V. Because we have ADC reference voltage maximum 2.5V

this is my understanding.
If output of sensor is 36mv for 500psi @3.6V
then output volt per psi would be 36mv/500 = 0.072mV ??

Can any one please help me understanding and designing this?
I am looking on INA333 instrumentation amplifier.

thanks in advance.

 

[barry]

Based on what you say previously, yes, it's .072mV/PSI. Or, just look at it this way: 36mV full-from the sensor; 2.5V full-scale for the ADC, so your amp needs a gain of:

2.5/.036=69.4

 

[Prasanna hegde]

thanks a lot for taking a look on the post Barry !

I did the calculation about gain using the INA333 datasheet and the gain factor is the same as you mentioned, 69.444.
datasheet is here https://www.ti.com/lit/ds/symlink/ina333.pdf

I am kind a new to designing these stuff like sensor output signal conditioning and amplification. I downloaded the Pspice model from Texas instrument and tried to simulate it.
To simulate the pressure sensor output, i used 4 resistor bridge and changed the value such a way that the Delta V between Vout+ and Vout- is 18mV.
But the amplifier output is doesn't look proper. It reaches 3.6V level even though the reference is 2.5V.

Could you please help in designing this by putting a sketch?
Here what I did..



I hope the image is uploaded.

Please help.

 

[barry]

You're amplifier is obviously being driven to the rail. For one thing, I think your Vref wants to be 1/2 the supply, 1.8V not 2.5. Trying setting your bridge to zero output(R5=R6) and see what comes out of the amp, it should be 1.8V.

 

[FARRUKHKHAN]

how to calculate the value of resistances which are going to used for a particular design of Instrumentation amplifier .........i have made two stage CMOS Op amp and now i want to make instrumentation amplifer but problem is how to take the values of resistances to make all the MOS working in saturation to get max gain ad after that adjust the gain according to gain formuala of 3 op amp instrumentation amplifier.....but to how to take values of resistances ........