I would like some advice on how to solve the following problem. The following circuit is motor driver with current sense circuit. The circuit run motor at cca 30mV when is not under load, but when the load is applied to motor, measuring voltage rise up to 500mV, hold It for 2 second and shut down driver. When I want to measure voltage between "unstable point" and gnd there is a big problem with stability. When i measure voltage with FLUKE 179 multimeter and original test probes I get cca 500 mV under load which is good.
If I add an extra crocodile wire (10-20cm) to test probes there is cca +- 100mV difference in measurement. Only if I add 1M Ohm resistor between "unstable point" and crocodile wire and 1M Ohm resistor between gnd and second test probe, I can add an extra crocodile wire after resistors and the measurement is right (+- few mV difference).
If I add cca 20cm extra crocodile wire on "unstable point", then add 1M Ohm resistor between crocodile wire and test probe, there is again +- 50-100 mV difference in measurement (even if there is a 1M Ohm resistor connected after 20cm crocodile wire). If I add 1M ohm resistor only on "unstable point" and not to gnd probe, there is also cca 50mV difference. Also I notice that if I touch "unstable point" with my hand, voltage on that point collapses so I suspect that the noninverting op amp circuit is unstable or the voltage range of measuring (30mV - 500mV) is to low to handle external disturbances. It's funny that crocodile wire without any load connected between multimeter probes and "unstable point" effect on measurement.