Relay (Simulink Reference)

Switch output between two constants

Library

Discontinuities

Description

The Relay block allows its output to switch between two specified values. When the relay is on, it remains on until the input drops below the value of the Switch off point parameter. When the relay is off, it remains off until the input exceeds the value of the Switch on point parameter. The block accepts one input and generates one output.

The Switch on point value must be greater than or equal to the Switch off point. Specifying a Switch on point value greater than the Switch off point value models hysteresis, whereas specifying equal values models a switch with a threshold at that value.

Data Type Support

The Relay block accepts real or complex signals of any data type supported by Simulink, except Boolean. The Relay block supports fixed-point data types.

For a discussion on the data types supported by Simulink, refer to Data Types Supported by Simulink in the Using Simulink documentation.

Parameters and Dialog Box

The Main pane of the Relay block dialog appears as follows:

Switch on point: The "on" threshold for the relay. The Switch on point parameter is converted to the input data type offline using round-to-nearest and saturation.
Switch off point: The "off" threshold for the relay. The Switch off point parameter is converted to the input data type offline using round-to-nearest and saturation.
Output when on: The output when the relay is on.
Output when off: The output when the relay is off.
Enable zero crossing detection: Select to enable zero crossing detection to detect switch-on and switch-off points. For more information, see Zero Crossing Detection in the Using Simulink documentation.
Sample time (-1 for inherited): Specify the time interval between samples. To inherit the sample time, set this parameter to -1. See Specifying Sample Time in the online documentation for more information.

The Signal data types pane of the Relay block dialog appears as follows:

Output data type mode: Specify the output data type and scaling to be the same as the inputs, or inherit the data type and scaling by backpropagation. Lastly, if you choose Specify via dialog, the Output data type, Output scaling value, and Parameter Scaling parameters become visible.
Output data type: Specify any data type, including fixed-point data types. This parameter is only visible if you select Specify via dialog for the Output data type mode parameter.
Output scaling value: Set the output scaling using binary point-only or [Slope Bias] scaling. This parameter is only visible if you select Specify via dialog for the Output data type mode parameter, and is only enabled if you select Use specified scaling for the Parameter Scaling parameter.
Parameter Scaling

Use Specified Scaling--This mode allows you to specify the output scaling in the Output scaling value parameter
Best Precision: Vector-wise--This mode produces a common binary point for each element of the output vector based on the best precision for the largest value of the vector.

This parameter is only visible if you select Specify via dialog for the Output data type mode parameter.

Characteristics

Direct Feedthrough
Yes

Sample Time
Specified in the Sample time parameter

Scalar Expansion
Yes

Dimensionalized
Yes

Zero Crossing
Yes, if enabled.

Direct Feedthrough	Yes
Sample Time	Specified in the Sample time parameter
Scalar Expansion	Yes
Dimensionalized	Yes
Zero Crossing	Yes, if enabled.

Relational Operator Repeating Sequence