I'm doing low side current measurement over a 0.1ohm resistance. Load is a DC motor powered with 12V.
Cable length between resitor and power supply ground ~60cm
I get a voltage of :
- 75mV => 750mA using power supply current info
- 75 mV => 750mA using multimeter measuring resistance voltage drop
- 100 mV => 1A using multimeter measuring voltage drop between resistance and ground on power supply (60cm of cable between resistor terminal and power supply GND)
- 100 mV => 1A using DSO-X 2014A oscilloscope and doing single ended measurement
- 75 mV => 750mA using DSO-X 2014A oscilloscope and doing differential measurement (using 2 probes and A-B math function)
Here is a scope capture with single ended measurement (average down with lower horizontal sensitivity) :
Measures done :
- in single ended measurement (with oscilloscope ground connected to power supply)
- with multimeter when it measures on COM connected to power supply ground
shows influence of cable length. Cable is classic cable of 3mm diameter, 60cm length?
How can we precisely explain this difference?