# Variable Resistor

Linear variable resistor in electrical systems

• Libraries:
Simscape / Foundation Library / Electrical / Electrical Elements

## Description

The Variable Resistor block models a linear variable resistor, described with the following equation:

`$V=I·R$`

where:

• V is voltage.

• I is current.

• R is resistance, that is, the signal value at the control port.

Connections + and - are conserving electrical ports corresponding to the positive and negative terminals of the resistor, respectively. R is a physical signal input port that controls the resistance value. The current is positive if it flows from positive to negative, and the voltage across the resistor is equal to the difference between the voltage at the positive and the negative terminal, V(+) – V(–).

### Variables

To set the priority and initial target values for the block variables prior to simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model. Using system scaling based on nominal values increases the simulation robustness. Nominal values can come from different sources, one of which is the Nominal Values section in the block dialog box or Property Inspector. For more information, see Modify Nominal Values for a Block Variable.

## Ports

### Input

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Input physical signal that specifies the resistance value.

### Conserving

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Electrical conserving port associated with the resistor positive terminal.

Electrical conserving port associated with the resistor negative terminal.

## Parameters

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The minimum resistance value. If the input signal falls below this level (for example, turns negative), this minimum resistance value is used. The parameter value must be nonnegative.

## Version History

Introduced in R2007a