Comparator_ Greater Than
- Gary Cane
Operator Menu Location: Signal Comparators
Operator Bitmap:
Functional Description:
The Greater-Than Comparator operator compares two analog input signals. Its digital output is set HIGH if input x1 exceeds x2 , and it is set to LOW otherwise. The output state will change only if the evaluated (>) 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 comparison dead-band, T is the switching dead-time, and t is the loop sampling time.
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 Greater-Than 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 
and while 
since the greater-than condition is not met. It also remains LOW while 
because the greater-than condition is not maintained for at least two seconds. The output does not switch to HIGH until t=12, when 
for more than two seconds. The output remains HIGH while 
because the greater-than condition is met (within the dead-band, i.e., 5.0 + 1.0 > 5.5). At time t=20 seconds, input x1 is less than x2 , but the output does not switch to LOW until t=22 seconds (when the less-than condition has been maintained for at least two seconds). The output will switch to HIGH (and remain HIGH thereafter) at time 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 dead-band, B
Switching Dead-Time. The length of time a signal must satisfy the comparison 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 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