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# linear variable resistor but output voltage is not linear

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#### johnburford

##### Banned
when making a resistance vs voltage chart of variable resistors connected to different kinds of circuits. Measuring the resistance of the variable pots wiper position compared to the output voltage of the circuit has a different curve compared to the linear resistance of the pots wiper. The variable resistor is linear but the output voltage of the circuit is nonlinear voltage or has a voltage curve. The resistance rotation that is linear is not proportional with the output voltage of a circuit when plotting the instantaneous voltages against the variable pots rotation resistance. Any reasons why circuits change a linear pot into a nonlinear or is not proportional with the output voltage of a circuit or network. I'm not sure what type of test this is called or done but I'm sure R&D engineers do it when prototyping boards.

Show us a circuit; your description is not making much sense. I have no idea what "rotation resistance" is. And you are talking about "circuit or network"--show us the circuit or network in question. My guess is your problem is HOW you are applying this device

The only thing linear means here, is resistance from wiper
to end vs angle. Any other expectation on your part is
misplaced.

Make Rpot an expression such as rW_end1=K*angle and
put that Rpot appropriately into your circuit node voltage
equations. If it "should" be linear then you would see a
form with a single Rpot term in the numerator (with perhaps
some multiplier). Anything else, don't be expecting linearity.

A potentiometer having a B after its value is linear. When it has a A then it is logarithmic for an audio volume control.
To find out for sure, turn it to halfway and measure the resistance from each end to its wiper. if they are the same then it is linear.

Take any circuit that has multiple variable pots. Make a graph of the variable pot from min to max on the graph by turning the pot from min to max and graph the resistance curve. Now turn the pot from min and max and measure the output voltage and graph the min and max voltage. The pots resistances from min to max range is not proportional or aligned with the output voltage min to max range. The pots resistance from min to max range graph is no proportional or aligned with the output voltage min to max range graph of the stage or circuit. The pots resistance range has it's curve and the output voltage of the stage or circuit has its curve. Both curves don't match or aren't proportional to each other. The pot resistance is linear but the output voltage of the stage is non-linear. I have noticed this problem on my circuits that uses variable resistors or pots compared to the output voltage of the stage or network that the variable linear resistor is connect to.

Take any circuit that has multiple variable pots. ......

can you give the circuit on which you have conducted the test ?

can you give the circuit on which you have conducted the test ?

And that statement: "take any circuit..." is sure confusing.

While the OP is still busy telling his circuit, I suggest to look at simple voltage divider.

Code:
V2 = V1 * R2/(R1+R2)

If you vary either R1 or R2, the relation between R1 or R2 and V2 is nonlinear. Something of this kind may have been observed.

While the OP is still busy telling his circuit, I suggest to look at simple voltage divider.

Code:
V2 = V1 * R2/(R1+R2)

If you vary either R1 or R2, the relation between R1 or R2 and V2 is nonlinear. Something of this kind may have been observed.

That would be my guess too. That's why EVERYBODY here keeps asking him to post one of his "any circuits".

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