Potentiometer

Rotary or linear-travel potentiometer controlled by physical signal

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Libraries:
Simscape / Electrical / Passive

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:

$$R_{WL}=\frac{R_0-2r}{x_{\max }-x_{\min }}\left(x-x_{\min }\right)+r$$

where

• R_WL 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.

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

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

• r is the residual resistance. This is the resistance between the wiper and port L when x is equal to x_min. This is also the resistance between the wiper and port R when x is equal to x_max.

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

$$R_{WL}=\{\begin{array}{ll}A\left(e^{\lambda \left(x-x_{\min }\right)}-1\right)+r\hfill & \text{if resistance gradient is higher at R}\hfill \\ R_0-A\left(e^{\lambda \left(x-x_{\min }\right)}-1\right)-r\hfill & \text{if resistance gradient is higher at L }\hfill \end{array}$$

where A and λ are chosen such that R_WL at x_max is R₀ - r, and R_WL at x = (x_max + x_min) / 2 is equal to R_av, 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

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

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

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

Examples

PWM Circuit Using 555 Timer

A pulse-width-modulated (PWM) output implemented using a 555 Timer in astable mode. The duty cycle is set by a potentiometer, P1. The potentiometer is controlled during run-time via Duty Cycle Control Knob. The scope shows the resultant output from the 555 Timer. To end the simulation, click on the Stop button.

• Open Model

Ports

Input

x — Wiper position control

physical signal

Physical signal input port controlling the wiper position.

Conserving

L — Left pin

electrical

Electrical conserving port associated with the potentiometer left pin.

R — Right pin

electrical

Electrical conserving port associated with the potentiometer right pin.

Dependencies

To enable this port, set Number of visible ports to Three: left, right, and wiper.

W — Wiper pin

electrical

Electrical conserving port associated with the potentiometer wiper pin.

Parameters

Number of visible ports — Ports visibility option

Three: left, right, and wiper (default) | Two: left and wiper

Whether to enable the right end port of the potentiometer, R.

Total resistance — Total resistance

1000 Ohm (default)

Resistance between port L and port R when port W is open-circuit.

Dependencies

To enable this parameter, set Number of visible ports to Three: left, right, and wiper.

Residual resistance — Residual resistance

1 Ohm (default) | positive scalar

Resistance measured between the wiper and the adjacent end port (L or R) when the wiper is at the end port. You can use this parameter to represent the inability of the wiper to reach the end of the track due to the mechanical stop. This value must be greater than or equal to zero. A typical value is 5e-3 times the total resistance.

Dependencies

To enable this parameter, set Number of visible ports to Three: left, right, and wiper.

PS input for wiper at L — PS input for wiper at L

0 (default)

Value of the input physical signal at port x that corresponds to the wiper being located at port L.

Dependencies

To enable this parameter, set Number of visible ports to Three: left, right, and wiper.

PS input for wiper at R — PS input for wiper at R

1 (default)

Value of the input physical signal at port x that corresponds to the wiper being located at port R.

Dependencies

To enable this parameter, set Number of visible ports to Three: left, right, and wiper.

Minimum resistance — Minimum resistance

1 Ohm (default)

Minimum permissible resistance measured between the wiper and the left port, L, when the wiper is at the left port. The value of this parameter must be greater than 0 and lower than the value of the Maximum resistance parameter.

Dependencies

To enable this parameter, set Number of visible ports to Two: left and wiper.

Maximum resistance — Maximum resistance

999 Ohm (default)

Maximum permissible resistance measured between the wiper and the left port, L. The value of this parameter must be greater than 0 and greater than the value of the Minimum resistance parameter.

Dependencies

To enable this parameter, set Number of visible ports to Two: left and wiper.

PS input for wiper at minimum resistance — PS input for wiper at minimum resistance

0 (default)

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

Dependencies

To enable this parameter, set Number of visible ports to Two: left and wiper.

PS input for wiper at maximum resistance — PS input for wiper at maximum resistance

1 (default)

Value of the input physical signal at port x that corresponds to the wiper being located the furthest from port L.

Dependencies

To enable this parameter, set Number of visible ports to Two: left and wiper.

Taper — Resistance taper behavior

Linear (default) | Logarithmic

Resistance taper behavior of the potentiometer.

Note

Linear and Logarithmic options do not model the same taper. You cannot parameterize the logarithmic potentiometer as a linear potentiometer, because the logarithmic taper is nonlinear.

If you set this parameter to Linear, this plot shows the relationship between the wiper control position and the resistance between L and W ports.

If you set this parameter to Logarithmic, this plot shows the relationship between the wiper control position and the resistance between L and W ports.

Resistance when centered — Resistance when centered

200 Ohm (default)

If you set the Resistance gradient parameter to Higher at L, this parameter is the resistance between port L and port W when the wiper is centered. Otherwise, if you set Resistance gradient to Higher at R, this parameter 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.

Dependencies

To enable this parameter, set Taper to Logarithmic.

Resistance gradient — Resistance gradient

Higher at R (default) | Higher at L

Whether the potentiometer resistance varies more rapidly at the left or the right end.

Dependencies

To enable this parameter, set Taper to Logarithmic.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2010a