Rockwell Automation Publication 2080-UM004D-EN-E - March 2018 35
High Speed Counter – 2080-MOT-HSC Chapter 4
• Also, the rate may be calculated many times over during the course of one
backplane scan time. This means that the rate data is obtained at a
backplane scan is only that of the very last pair of pulses and disregards the
other rate calculations that have happened during that interval. This is
especially problematic if the pulses during the update time are unevenly
spaced, the reported rate could be based entirely on two pulses which are
extremely close together (a very high rate) but a third pulse was separated
by a greater time (low rate).
You must understand these limitations when using HSC_PULSE_WIDTH_Bn
to derive a rate.
1 ms
1 ms
1 ms
1
2
3
4
1
2
1000 Hz
2000 Hz
1
1000 Hz
PresentCount_n
⌂Count
PresentRate_n
0
Per Pulse Errors
(1)
(1) This table does not represent accuracy per pulse but repeatability. This repeatability can be applied in No
Filter setting.
Real pulses
(note 1.9999 can
be rounded to 2)
Pulses
reported by
module
Real
Frequency
Reported
Frequency
% Error
2 1 500 kHz 1 MHz 100%
9 10 111 kHz 100 kHz 11.1%
101 100 9.901 kHz 10.000 kHz 1.00%
1001 1000 999 Hz 1000 Hz 0.10%
9,999 10,000 100.01 Hz 100.00 Hz 0.010%
99,999 100,000 10.00010 Hz 10.00000 Hz 0.001%
Maximum Cyclic Rate Errors
Update Time
Value Scalar
Frequency
100 Hz 1 kHz 10 kHz 100 kHz 1 MHz
1 NA NA 20.02% 20.02% 0.210%
10 NA 20.11% 2.020% 0.210% 0.030%
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