Introduction
From cheap e-Bay to precision linear, potentiometers are ubiquitous electronic components. They are versatile devices. Often being used as simple inputs but some can be capable of very accurate position measurements.
Even though the external appearance can vary significantly the underlying principle of operation is the same. Generally, they are encountered as three-pin devices. In-circuit schematics, they are represented with a resistor symbol with an additional arrow on the side
Up to four precision potentiometers can be connected to a single MonoDAQ-U-X device. If high precision is not necessary – for example, using cheap rotary potentiometers as controls for the MonoDAQ-U-X then up to eight potentiometers can be connected to the device.
Operation
The circuit symbol gives a good hint of the operation of the potentiometer.
A potentiometer contains a resistive element (hence the resistor symbol). When the resistive element is connected to an excitation (Vin and GND) a voltage gradient forms over the resistive element.
The third contact is called a wiper. The wiper makes electrical contact with the resistive element and slides over it when the potentiometer is moved/rotated. The wiper’s potential depends on where on the resistive element it is located.
All of this forms an adjustable voltage divider. By moving the potentiometer the Vout potential will smoothly change from GND to Vin.
This property is what makes the potentiometer a very useful device. By measuring the Vout potential we can easily calculate the position (distance) of a linear potentiometer or the angle of a rotary potentiometer
A note about the term “linear”
Describing a potentiometer as linear can cause a bit of confusion as it can actually mean two different things!
It can mean that the motion of the potentiometer is linear (as opposed to rotary)
Or it can mean that the resistance vs position is a linear relationship (as opposed to for example exponential)
When using the term linear in this manual we are referring to the former. As long as you are using potentiometers as measurement devices they will always be linear in the latter meaning.
Connecting the potentiometer
Knowing how the potentiometer works should make the connection easy. Before we connect it to the MonoDAQ-U-X we need to…
Identify the wires/pins
The best way to know how to connect your potentiometer is to consult the datasheet. In case this is not an option, a multimeter can be used to help you.
Set the multimeter to the resistance measuring mode and connect it to any of the two pins. Measure the resistance while moving the potentiometer. Repeat this for all three of the two-pin combinations.
Find the two pins where the resistance stays constant while moving the potentiometer. These are the pins connected to the potentiometers resistive element. They should be connected to the excitation (GND and Vin).
The remaining pin is the wiper and should be connected to the Voltage Input channel of the MonoDAQ-U-X.
Connecting to the MonoDAQ-U-X
The Excitation channel is set to a 10V excitation. The input channel is set to single buffered with a 10V range.
