A potentiometer is a variable resistance device where the resistance between two end contacts is fixed and a wiper provides a tapping point part way between the two contacts.
They are used in a variety of applications, for example making adjustments to a parameter or to emulate a variable control.
For applications where the requirement is to simply provide a variable resistor (the equivalent of linking the wiper to one terminal of the potentiometer) then these can be emulated by any of Pickering Interfaces resistor modules. For applications where the user needs to emulate all three terminals then the user has to approach the problem in a different way.
Emulating a Potentiometer
Emulation of the potentiometer requires the use of two separate variable resistor channels connected in series. For a Pickering Interfaces resistor module these will both need to be a variable resistor channels that have a maximum resistance that is greater than the resistance of the potentiometer to be emulated.. The user software needs to control the two channels so that the sum of the two channels is always the same value (e.g. 10 kOhm).
For resistor modules that use resistance calls this is a straight forward process, one resistor channel is set to the resistance required for the wiper, the other is set to the potentiometer resistance less the wiper resistance.
- Example. If the potentiometer is to be 10kOhms and the wiper is to be at 1kOhm then one resistor needs to be programmed to 1kohm and the other to 9kOhm
Some resistor modules use binary calls to set resistance value, the LSB of which is based on the setting resolution. For these modules the user needs to calculate the binary values corresponding to the wiper setting and the binary value corresponding to the potentiometer value. One resistor channel is set to the wiper binary value, the other is set to the binary potentiometer value less the binary wiper value.
- Example. If the potentiometer is to be 10kOhms and the wiper is to be at 1kOhm and the module resolution is 1 Ohm then one resistor needs to be programmed to binary 1000 and the other to binary 9000.
The 40-296 is based on the 40-295 and offers a configuration where two resistor channels are wired together to emulate a potentiometer. In general we suggest that users choose 40-297 or 40-295 (or PCI equivalents 50-297 and 50-295) in preference since the same functionality can be achieved by the user wiring the channels together externally and having the freedom to reconfigure to separate channels for other applications, or to mix potentiometer and variable resistor channels in the same module.