Omron CJ1W-CT021 Operation Manual page 105

Extra Functions
Rate Value Calculation
Count Pulses
Time Base
Counter Value (T0)
If you want to use Rate Measurement for a Counter you must start by defining the
Time Window. You can set the Time Window between 1 ms and 9999 ms, in steps
of 1 ms (BCD). The number of pulses which are received during the Time Window
are automatically calculated by subtracting the Counter Value at the beginning of
the Time Window from the Counter Value at the end of the Time Window.
T0
Time Window
Current
CCV = Current Counter Value
Time Window = [1, 9999 ms]
Rate Measurement can be done for all Input Signal Types (refer to 3-3 "Input Sig-
nal Types"). Calculating the Rate Value in this way implies that a change of the
counting direction during the Time-Window is reflected in the Rate Value. For illus-
tration refer to the next example:
The Counter Value (T0) at the beginning of the Time-Window is +5. During the
Time-Window 5 up counts and 15 down counts are received. The Counter Value
(T1) at the end of the Time-Window will then be –5. The Rate Value is –10.
Note 1. For Phase Differential Signals (multiplication x2 and x4) pulses are counted on
both edges of A or both edges of A and B respectively. If you want to calculate
the pulse Rate Value for these signals, you must divide the measured Rate Val-
ues by 2 and 4 respectively.
2. The pulse rate after presetting or resetting a counter will be the pulse rate cal-
culated just prior to presetting or resetting.
3. Calculations will be correct when a Ring Counter rolls over (goes from maxi-
mum value to 0 or from 0 to maximum value).
4. The measurement interval normally varies by 125 µs and can vary by a maxi-
mum of 1 ms. If this variation becomes a problem, it is recommended that the
pulse rate value be averaged in the ladder program.
T1
Current
Counter Value (T1)
Rate Value 1 = CCV ( T1) - CCV (T0)
Rate Value 2 = CCV ( T2) - CCV (T1)
...
Rate Value n = CCV ( Tn) - CCV (T(n-1))
T2
Time Window
Current
Counter Value (T2)
Section 3-7
85