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# Potentiometer

Model rotary or linear-travel potentiometer controlled by physical signal

Passive Devices

## Description

The Potentiometer block represents a rotary or linear-travel potentiometer, with the wiper position controlled by the input physical signal.

If the potentiometer resistance changes linearly based on wiper position, then the resistance between the wiper position and port L is:

${R}_{WL}=\frac{{R}_{0}}{{x}_{\mathrm{max}}-{x}_{\mathrm{min}}}\left(x-{x}_{\mathrm{min}}\right)$

where

• RWL is the resistance between the wiper position and port L.

• R0 is the total resistance between ports L and R.

• x is the wiper position.

• xmin is the value of the wiper position when the wiper is at port L.

• xmax is the value of the wiper position when the wiper is at port R.

If you specify LOG for the potentiometer resistance Taper parameter, then the resistance between the wiper position and port L is:

where A and λ are chosen such that RWL at xmax is R0, and RWL at x = (xmax + xmin) / 2 is equal to Rav, the resistance when the wiper is centered.

 Note:   Potentiometers widely described as LOG or logarithmic taper are, in fact, exponential taper. That is, the gradient of the resistance between wiper and left-hand port increases as the resistance increases. The Potentiometer block implements this behavior.

For both linear and logarithmic tapers, the resistance between the wiper position and port R is:

${R}_{WR}={R}_{0}-{R}_{WL}$

where

• RWR is the resistance between the wiper position and port R.

• R0 is the total resistance between ports L and R.

• RWL is the resistance between the wiper position and port L.

## Dialog Box and Parameters

Total resistance

The resistance between port L and port R when port W is open-circuit. The default value is 1000Ω.

Residual resistance

The lower limit placed on the resistance between the wiper and the two end ports. It must be greater than zero. A typical value is 5e-3 times the total resistance. The default value is 1Ω.

Resistance when centered

This parameter is available only if you select LOG for the Taper parameter. If you select Higher at R for the Resistance gradient parameter, then Resistance when centered is the resistance between port L and port W when the wiper is centered. Otherwise, if you select Higher at R for the Resistance gradient parameter, then Resistance when centered is the resistance between port R and port W when the wiper is centered. Because the resistance taper is exponential in shape, the value of the Resistance when centered parameter must be less than half of the Total resistance parameter value. The default value is 200Ω.

PS input for wiper at L

The value of the input physical signal at port x that corresponds to the wiper being located at port L. The default value is 0.

PS input for wiper at R

The value of the input physical signal at port x that corresponds to the wiper being located at port R. The default value is 1.

Taper

Specifies the potentiometer resistance taper behavior: LIN (linear) or LOG (logarithmic). The default value is LIN.

Specifies whether the potentiometer resistance varies more rapidly at the left or the right end: Higher at L or Higher at R. This parameter is available only if you select LOG for the Taper parameter. The default value is Higher at R.

## Ports

The block has the following ports:

L

Electrical port representing the left pin

R

Electrical port representing the right pin

W

Electrical port representing the wiper pin

x

Physical signal input port controlling the wiper position