hi,
The circuit adopts positive and negative 9V power supply. When the power supply has no obvious glitch, the chip works normally.
When the power supply has large glitches (peak-to-peak value is 720mV, glitch cycle is 16.6us), the voltage on pin 6 of the chip is not stable.
Use a multimeter to measure:
Pin 6 has an unstable voltage, sometimes the output reaches 2V, sometimes the output reaches -2V.
When moving the meter, there are fluctuations of several tens of mV. Even if you do not move the meter, the voltage will fluctuate and become unstable. In theory, 0V should be output. The multimeter is working properly.
Observe using the oscilloscope, pin 6 output voltage is still 0V, but there is a large glitch at 0V, glitch voltage peak-to-peak about 620mV.
problem:
1 In this case, why the output voltage of Pin 6 is unstable (measured by the multimeter), and the waveform observed by the oscilloscope is normal.
2 In addition to reducing the glitch voltage, are there other solutions to this problem? Make INA122U output voltage normal, no abnormal fluctuations.
3 This phenomenon is not determined by the internal circuit characteristics of the INA122U.
4 If do not use the INA122U, please recommend an instrumentation amplifier with other signals. Magnification G=200K/Rg 1