Comparator_ Not Equal

Operator Menu Location: Signal Comparators

Operator Bitmap:
 

Functional Description:
The Inequality Comparator operator compares two analog input signals. Its digital output is set LOW if the signals are equal (i.e., within a user-defined dead-band); and it is set HIGH if they are not. The output state will change only if the inequality/equality 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 x2 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). It remains LOW while since the signals are equal to each other. It also remains LOW while because the input signals are within the dead-band B=1.0. And, it remains LOW while because the inequality condition is not maintained for at least two seconds. Similarly, the output stays LOW while (signals within dead-band), while (inequality condition not maintained for two seconds), and while (signals within dead-band). The output does not switch to HIGH until t=22, when the two signals are not equal for more than two seconds. At time t=25 seconds, the input signals satisfy the equality condition, but the output does not switch to LOW until t=27 seconds. The output remains LOW thereafter.

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 inequality (equality) 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