Hello
I am making a circuit with non-inverting summing amplifier in prototyping board.
When I was testing the circuit, two input of the summing amplifier were 133mV and -125mV, but after summing the output value was -258mV, it looks like the amplifier inverted 133mV to -133mV then add the two signal together... I repid the testing many times and checked all the connection of the circuit, but still give the same output...
Anybody had the same problem? Or knows what might be the reason cause this problem?
Thanks a lot!!!

 

Can you post the circuit?

Summing amps are nearly always inverting. Each input sees 0 volts at the summing junction, so the summed signals have no effect on each other.

 

The results you are getting are exactly right for an inverting summing amplifier. Apparently you built it correctly and simply do not understand it.

 

The results you are getting are exactly right for an inverting summing amplifier. Apparently you built it correctly and simply do not understand it.

133mV added to -125V is 8mV. An inverting summing amp would make that -8mV. Our OP got -258mV.
It appears to me that measurement error(s) are involved.
Chudiandeyu, we need to see a schematic of the circuit you used.

 

Oops. Caught me making a mistake...again!

 

how to upload a picture?

 

Hi, thanks for all your answers, I already solved the problem
there is one point for the input signal i didn't solder well, so one of the signal cannot go to the summing amplifier. After i fixed the soldering, it is working well now It was really stupid of me ~~
Thank you all