Comparator_ Equal

Operator Menu Location: Signal Comparators

Operator Bitmap:
 

Functional Description:
The Equality Comparator operator compares two analog input signals. Its digital output is set HIGH if the signals are equal (i.e., within a user-defined dead-band); and it is set LOW if they are not. The output state will change only if the equality/inequality condition is maintained for a user-specified length of time---the switching dead-time. That is, the output is defined by

where y is the digital output, x1 and are the analog inputs, B is the equality dead-band, T is the switching dead-time, t is the loop sampling time, and where || denotes the absolute value operator.
For example, suppose that the initial output is y(0)=0, input signal x1 is fixed , the dead-band is set to B=1.0, the switching dead-time is set to T=2 seconds, and signal x2 has the following profile:

Under these conditions, the output of the Equality Comparator will be

A plot of the input signals and a plot of the operator output are shown next.

Initially, the output is y(0)=LOW (as specified by the initial condition property). The output remains LOW, until two seconds elapse (the switching dead-time). The output goes high after two seconds, y(2)=HIGH, and remains HIGH while because the input signals are within the dead-band B=1.0. It also remains HIGH while because the inequality condition is not maintained for at least two seconds. Similarly, it remains HIGH while (within dead-band) and while (inequality condition not maintained for two seconds). At t=20 seconds, the input signals satisfy the inequality condition, but the output does not switch to LOW until t=22 seconds. (when the input signals have remained unequal for at least two seconds.) Likewise, the output will go HIGH (and remain HIGH thereafter) at t=27 seconds.

User-Defined Properties:
Object Name. A string label that identifies the operator

Initial State. The output state (HIGH or LOW) at startup (at time t=0)

Dead Band. The equality dead-band, B

Switching Dead-Time. The length of time a signal must satisfy the equality (inequality) condition, for the output to switch from LOW to HIGH (from HIGH to LOW). The switching dead-time is denoted by T in the equation above, and is expressed in seconds.

Comments:
• Design Pad will issue an error on processing if the input pin is not connected
•The equality dead-band must be greater than or equal to zero, B>=0
•The switching dead-time must be greater than or equal to zero, T>=0

See Also:
>=, >, <=, <, and != Comparators; High/Low Alarm; Thresholding