Analog Comparison - Advantech iDAQ-900 Series User Manual

3.3.4

Analog Comparison

Some of the analog input modules provide analog comparison function. The compare
result can be routed to the chassis as a timing signal.
Analog comparison function compares one of the analog input signals to a preset
threshold value. If the analog input signal is higher than the threshold value, result
signal is high; otherwise, result signal is low. This is shown in Figure 3.14.
Figure 3.14 Analog comparison
To prevent a glitch of the analog comparison results due to noise in the analog input
signals, hysteresis values can be added to the threshold value. With hysteresis val-
ues, analog comparison results becomes high only when analog input signal
becomes higher than the upper threshold value; it becomes low only when analog
input signal becomes lower than the lower threshold value - it remains unchanged
otherwise.
Analog comparison can be selected as rising edge active or falling edge active. The
upper and lower threshold values are different with different active edge settings. For
rising edge active, the upper threshold value is equal to threshold value, and the
lower threshold value is equal to threshold value minus hysteresis value, as shown in
Figure 3.15. For falling edge active, the upper threshold value is equal to threshold
value plus hysteresis value, and the lower threshold value is equal to threshold value,
as shown in Figure 3.16.
Figure 3.15 Analog comparison with hysteresis, rising edge active
Figure 3.16 Analog comparison with hysteresis, falling edge active
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