GE RSTi-EP User Manual page 198

Chapter 5 Detailed Descriptions of I/O Modules
Additional Counter Functions
Comparison Function
Via the parameter Comparison function you can deactivate the comparison function or define a
comparison condition:
–– Counter value higher or equal comparison value
–– Counter value lower or equal comparison value
–– Counter value equal comparison value
To use the comparison function, you have to preset the comparison values for both counting
channels in the respective first double word of the process data outputs and to set the bit QX8.1 and
QX10.1 respectively (Comparison bit released) in each control word.
As soon as the counting value meets the corresponding comparison condition, the bits Comparison
bit active and Comparison condition met are activated. The bit Comparison bit active remains set as
long as the comparison condition is being met (respectively the parameterised hysteresis). The bit
Comparison condition met remains active until it will be reset with the bit Reset of the status bits in the
control word.
When using a counting mode with primary direction, the comparison bit will be set only upon
reaching the comparison value from the primary direction.
Hysteresis
It is possible to reduce frequent triggering of a process alarm and toggling of the comparison bit (e.g.
if the value of a sensor signal fluctuates around the comparison value), by setting the hysteresis. You
thereby define a range above and below a reference value (zero crossing, overflow/underflow and
comparison value), within which the status bit will not be reset.
A limit value between 0 and 255 can be parameterized for the hysteresis. With hysteresis = 3 for
example, all values differing less than 3 from the reference value are smoothed. Hysteresis is
deactivated with the values 0 and 1. The hysteresis is activated upon reaching the comparison
condition. The comparison result remains unchanged during active hysterersis until the counting
value reaches the predetermined hysteresis limit. After leaving the hysteresis range, hysteresis is
reactivated only upon reaching the comparison condition again.
GFK-2958E RSTi-EP User Manual 194