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Hit Crossing

Detect crossing point.

Library

Signals & Systems

Description

The Hit Crossing block detects when the input reaches the Hit crossing offset parameter value in the direction specified by the Hit crossing direction parameter. This block locates transitions to, from, and through the offset. The block finds the crossing point to within machine tolerance.

The block accepts one input of type double. If the Show output port check box is selected, the block output indicates when the crossing occurs. If the input signal is exactly the value of the offset value, the block outputs a value of 1 at that time step. If the input signals at two adjacent points bracket the offset value (but neither value is exactly equal to the offset), the block outputs a value of 1 at the second time step. If the Show output port check box is not selected, the block ensures that the simulation finds the crossing point but does not generate output.

The Hit Crossing block serves as an "Almost Equal" block, useful in working around limitations in finite mathematics and computer precision. Used for these reasons, this block may be more convenient than adding logic to your model to detect this condition.

The hardstop and clutch demos illustrate the use of the Hit Crossing block. In the hardstop demo, the Hit Crossing block is in the Friction Model subsystem. In the clutch demo, the Hit Crossing block is in the Lockup Detection subsystem.

Data Type Support

A Hit Crossing block outputs a signal of type boolean unless boolean compatibility mode is enabled (see "Enabling Strict Boolean Type Checking") in which case, the block outputs a signal of type double.

Parameters and Dialog Box

Hit crossing offset
The value whose crossing is to be detected.
Hit crossing direction
The direction from which the input signal approaches the hit crossing offset for a crossing to be detected.
Show output port
If checked, draw an output port.

Characteristics

Direct Feedthrough
 Yes
Sample Time
 Inherited from driving block
Scalar Expansion
 Yes
Vectorized
 Yes
Zero Crossing
 Yes, to detect the crossing


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