Option : Constant Current Sources; An Overview - Intab PC-Logger 3100i How To Use Manual

OPTION : Constant Current Sources

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AN OVERVIEW

Constant Current Sources have their natural use when measuring resistance.
A resistor is in itself passive and does not lend itself to be measured unless
special arrangements are made. It has to be tricked into revealing its value as a
voltage that can be measured and logged.
This voltage has to be proportional to the resistance.
An excursion in time, back to the old school days, may make you remember
"Ohm's Law". It states that U=R*I. I.e. "the voltage across a resistor is the
product of the current through it and its resistance".
Juggle the letters a bit and you get R=U/I (School maths again).
As current (I) is known and constant it is easily seen that measured voltage is
directly proportional to resistance.
The constant current is almost always set to 0.500mA. I.e. every measured mV
corresponds to 2Ω. Insert these values into the formula above and you get:
1mV/0.500mA=
10 -3 /0.5*10 -3
1/0.5 (V/A) =2Ω (V/A=Ω)! QED
Below is a schematic diagram of how a constant current source can be put to
work.
R
This method is called "four-wire resistance measurement".
How to do the practical wiring is shown in a later section in this manual.
(V/A)=
I
OPTION : Constant Current Sources
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U=R*I
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