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Remote sensing

Posted: June 24th, 2010, 8:41 am
by ramgen
I am trying to source voltage on one circuit and measure voltage on another circuit.
The measured voltage is always the value of the source value. Even if I place the sense leads to
different nodes in the circuit the measured voltage is the same as the source voltage.

Re: Remote sensing

Posted: June 24th, 2010, 8:56 am
by Dale C
Sourcing voltage and measuring voltage in the four wire mode is tricky in the SMU world.
First of all remember the SMU or Source Meter are not separate instruments. It can source Voltage and Current and it can measure Voltage and Current. But the for functions are tightly integrated and certainly are not separate and isolated.
Having a two resistors in series both 1k and having the source meter source voltage across both resistors is fine.
But using the four wire mode when sourcing and trying to measure voltage is a problem. It is not like a separate voltmeter. The sense lines now try to (with the internal control loop) try to force the source voltage value in the sense lines.
All this means is do not source voltage on one part of the circuit and try to measure voltage on another part of the circuit. The sense lines have the control circuitry to try to keep the sense lines at the source voltage value.
Sourcing current and measuring voltage is a much better solution.
However, even with this scenario the Model 2400 has a 5V limit between Sense terminals and Source terminals.
Look at the specification in the General Section
MAX VOLTAGE DROP BETWEEN INPUT/OUTPUT and SENSE TERMINALS :5V