I need an idea. I am trying to use a cheap pressure transducer MPX10 to measure pressures up to 10 kPa. I set out to use a standard 3 opamp instrument amplifier but came against a problem. The transducer has a span of 35mV for to 0 to 10kPa input but can have an offset of nearly as much I measure 25mV difference between +ve and -ve outputs with zero pressure.

This means that with the gain set to give 0.5 to 4.5 volts to an AD input the offset takes most of this range. I set the lower point by returning the Vref point to a pot to set zero.

How can I null out this offset

I have attached my circuit

 

Your setup will require the use of a commercial instrumentation amplifier. And they will also have in most cases have offset adjustment pins. In your schematic. You have made a instrumentation amplifier with discrete components. A proper instrumentation amplifier require the use of very closed matched resistors. And problems like you have now, are common then using discrete components. However you should also know all pressure sensors have some offset. So they need to be calibrated. If you plan to connect your sensor to some ADC. It is very simple to apply calibration in the software
Take a look at this link. It may help you http://www.analog.com/en/content/cu_dh_designers_guide_to_instrumentation_amps/fca.html

 

Google around for srain gage amplifiers or signal conditioners. Strange gages have been around even longer than me, there should be lots of stuff out there on them.

As t06afre said, rolling your own conditioner is folly despite the fact that years ago it was the only way. I vaguely recall 0.01% wirewound resistors aplenty.

Look at the Analog Devices AD624 (I'm sure there are many others too). It's a tad pricey at $35 and up, It'll lower your pain level from full blown migraine to toothache status.

 

I found 15 parts labeled as instrumentation amplifiers at www.mouser.com for under $2.