# Thermistor

Model NTC thermistor using B-parameter equation

Sensors

## Description

The Thermistor block represents an NTC thermistor using the B-parameter equation. The resistance at temperature T is

`$R={R}_{0}{e}^{B\left(1/T-1/{T}_{0}\right)}$`

where:

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

• B is the characteristic temperature constant.

The following equation describes the thermal behavior of the block:

`$Q={K}_{d}{t}_{c}\frac{dT}{dt}$`

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.

To model the thermistor in free space:

1. Connect the thermistor to the B port of a Simscape™ Convective Heat Transfer block.

2. Connect the A port of the Convective Heat Transfer block to a Simscape Ideal Temperature Source block whose temperature is set to the ambient temperature.

3. Set the Area parameter of the Convective Heat Transfer block to an approximate area Anom.

4. Set the Heat transfer coefficient parameter of the Convective Heat Transfer block to Kd/Anom.

## Dialog Box and Parameters

### Electrical Tab

Nominal resistance R0 at reference temperature T0

The nominal resistance of the thermistor at the reference temperature. Many datasheets quote the nominal resistance at 25°C and list it as R25. The default value is `1000` Ω.

Characteristic temperature constant B

The coefficient B in the equation that describes resistance as a function of temperature. The default value is `3500` K.

Reference temperature T0

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

### Thermal Tab

Thermal time constant

The time it takes the sensor temperature to reach 63% of the final temperature change when a step change in ambient temperature occurs. The default value is `5` s.

Dissipation factor

The thermal power required to raise the thermistor temperature by one K. The default value is `0.75e-4` W/K.

Initial temperature

The temperature of the thermistor at the start of the simulation. The default value is `298.15` K.

## Ports

The block has the following ports:

`A`

Thermal port

`+`

Positive electrical port

`-`

Negative electrical port