# Thermal Resistor

Resistor with thermal port

## Library

Electrical Elements

## Description

The Thermal Resistor block represents a temperature-dependent resistor. The resistance when the temperature at the thermal port is T is

R = R0(1+α(TT0))

where:

• R0 is the nominal resistance at the reference temperature T0.

• α is the temperature coefficient.

The following equation describes the thermal behavior of the block:

`$Q={K}_{d}{t}_{c}\frac{dT}{dt}-{i}^{2}R$`
where:

• Q is the net heat flow into port A.

• Kd is the Dissipation factor parameter value.

• tc is the Thermal time constant parameter value.

• dT/dt is the rate of change of the temperature.

• i is the current through the resistor.

### Variables

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

In particular, the Initial temperature variable lets you set a high-priority target for the temperature of the thermal resistor at the start of the simulation. The default value is `298.15` K.

## Parameters

Nominal resistance

The nominal resistance of the thermistor at the reference temperature. Many datasheets quote the nominal resistance at 25°C (298.15 K) and list it as R25. The default value is `1` Ω.

Reference temperature

The temperature at which the nominal resistance was measured. The default value is `298.15` K.

Temperature coefficient

The coefficient α in the equation that describes resistance as a function of temperature. The default value is `5e-05` 1/K.

Thermal time constant

The time it takes the resistor temperature to reach 63% of the final temperature change when a step change in ambient temperature occurs. The default value is `10` s.

Dissipation factor

The thermal power required to raise the thermal resistor temperature by one K. The default value is `0.001` W/K.

## Ports

The block has the following ports:

`A`

Resistor thermal port

`+`

Positive electrical port

`-`

Negative electrical port