Like after building l amplifier of that will produce some volts output can I test the same with a voltage source of 0 to. 30mV instead of actual device ?
How will the circuit behave?

 

Perhaps you could use a fixed resistor with a value a little less than R3 with a series potentiometer an order of magnitude less than R3 in place of the strain gauge to test?

 

Perhaps you could use a fixed resistor with a value a little less than R3 with a series potentiometer an order of magnitude less than R3 in place of the strain gauge to test?

Yeah.. that will work too
But when I tried with a voltage source it surprisingly worked but after a few minutes the voltage slowly got to +vsat . Not sure about the reason though..

 

hi 2k4,
Please post a diagram showing the circuit wiring.
E

 

Edit: I'll update the schematic soon
the last one wasnt clear enough

 

Here it is
the inputs are in+ and in- conncted to device

 

I tested it again and found a possibe reason:
when i connect a signal generator fixed at certain mV then there is no ground reference maybe that might cause offset which increases overtime.

 

hi 2k4,
Please post simple diagram showing how that circuit in post #7 is connectd to the OPA input.
E

But when I tried with a voltage source it surprisingly worked but after a few minutes the voltage slowly got to +vsat . Not sure about the reason though..

Where are you measuring this rising voltage?

 

hi 2k4,
This simple circuit will produce a ~30mV signal for testing.
E

Please post the specification of the load cell

 

There is, of course, a large range of loadcell devices, but taking a typical loadcell having an output of 2mV/Volt.

For a 10V reference, a nominal test voltage of 0 - 20mV is required.

The following circuit presents a nominal 5mA load on the exitation source and a nominal test range of -5mV to +100mV with the values given. (Plenty of headroom for over-range testing).

You can try the more common presentation of a three resistor circuit, (R3=0) but I can almost guarantee, you will struggle to get 0mV for zero input calibration.

Values are none critical (but keep in the same order).
The pot can be 500R to 50k and still work ok.
Adjust to suit.
(The exitation voltage is from the loadcell amplifier).

 

hi 2k4,
Please post simple diagram showing how that circuit in post #7 is connectd to the OPA input.
E



Where are you measuring this rising voltage?

I'll update the diagram soon
The rising voltage was measured in the VOUT node (right most in CMT diagram from post 6)

 

Coming back to this thread, I confess I've not really absorbed the detail of subsequent posts, but I'm wondering why my post #2 isn't the simplest and quickest way to test with a circuit which simply mimics the strain gauge?

Leaving that aside, why use 3 x OP07 op amps (first introduced around 50 years ago, excellent for their time) when a number of high performance comparatively inexpensive intrumentation amplifiers exist today? Also, what is happening with the output? If it's going via ADC into a processor all components can be fixed and calibration done with firmware constants.

 

Coming back to this thread, I confess I've not really absorbed the detail of subsequent posts, but I'm wondering why my post #2 isn't the simplest and quickest way to test with a circuit which simply mimics the strain gauge?

Leaving that aside, why use 3 x OP07 op amps (first introduced around 50 years ago, excellent for their time) when a number of high performance comparatively inexpensive intrumentation amplifiers exist today? Also, what is happening with the output? If it's going via ADC into a processor all components can be fixed and calibration done with firmware constants.

I haven't explored any replacements yet
I would like your recommendations
so please suggest some replacements

and Thanks in advance !

 

hi 2k4,
Please check this LTS simulation circuit for accuracy, compared to post#6.

I have omitted the OP07 balancing circuits and set the variable resistors to their max value.

What signal drives the transformer???

E
View attachment 353115

check this out:


it is CM noise filter

I tried powering the circuit without that picks up too much noise causing unstability.

 

hi 2k4,
I need to know the primary and secondary inductances for the transformer.?

What are the electrical parameters of that input signal?

E

 

hi 2k4,
I need to know the primary and secondary inductances for the transformer.?

What are the electrical parameters of that input signal?

E

Edit:


Input signal is supposed to varyin mV and produce amplified outputs correspondingly

 

so please suggest some replacements

Maybe a dedicated instrumentation amplifier like the INA333 or INA826. Or OPA197, OPA2333, OPA333, LT1013. And depending on what you are doing with the output, if you are converting to digital, calibration (including linearisation if required) and offset in firmware. People use tricks to compensate for hysteresis and display zero if it's nearly zero!