Strain Gauge Ampliferying problems

Motaz Ayyad

Hi,

i am working on strain gauge training kit which will help the incoming students after me to apply the concepts of one of the force sensors

but since i live in the 3rd world none of the instrumentation amplifiers are available such as INA122...etc

the only Op/Amps available are :
LM358
LM386
LM324
uA741
TO072

and i know most of them are poor
i used LM358 as first amplification which made a gain approx 100 then i used anther one but it ends up with complete unstable system

and i am thinking of building instrumentation amplifier from one of the above Op/Amps

but i have no idea about how? that's my problem or if anyone could have another solution

thanks you and sorry for my bad English

Hal Albach

Try Googling "LM358 Instrumentation Amplifier Circuits"

Motaz Ayyad

i tried to build the circuit in the attachment with LM358 instead of uA741
and with another different thing which is i used +6 and 0 as power to the amps instead of +12 -12

the output was constant to approx 4.42V

thanks you for reply

kwinn

Motaz Ayyad wrote: »

i tried to build the circuit in the attachment with LM358 instead of uA741
and with another different thing which is i used +6 and 0 as power to the amps instead of +12 -12

the output was constant to approx 4.42V

thanks you for reply

Take a look at the attached LM358 data sheet. Try the "High Impedance Differential Amplifier" circuit on page 5.

Hal Albach

This site has information on using a LM358 for a an instrumentation amplifier and includes a circuit for a strain gauge.

http://www.scribd.com/doc/14256112/AN002OpAmp-LM358-as-Instrumentation-Amplifier

Genetix

The LM386 is a Power Amplifier designed to drive speakers.
The LM324 is a Quad version of the LM358. Both use less current than the TL072.
The 741 can only pull its output to within about 2V of its positive and negative supply voltages.