Rockwell Automation 1746-HSCE2 Multi-Channel High Speed Counter Module - Manual (Page 31)

Publication 1746-UM002B-EN-P - August 2004
Module Operation 2-11
Additional checks ensure that rates below 1 Hz, which are not
supported by the module, and frequencies due to motor vibration, are
not counted in the rate value calculation.
Accuracy
The accuracy of the rate value can be ±0.005% (typical). For this
resolution, the rate measurement value must be transferred in
single-precision floating-point format. This format is only available
when the module operates as Class 4. Fractional rates, those between
1 and 0 or -1 and 0, are not reported.
The rate measurement value can also be transferred as an integer
value. The integer format is available in both Class 1 and Class 4.
Output Control All eight outputs can be controlled by any or all of the counters, or
they can be controlled by the user program. When controlled by a
counter, an output can be programmed to turn on or off based on the
count value and/or rate value of the counter.
The eight outputs are divided into four real outputs and four virtual
outputs. The outputs can be activated from the user program or from
the module in response to specified input events. The status of the
real outputs is available to the user program. The virtual outputs are
available only to the user program. They have no real output
associated with them. The real outputs are protected from overloads
by a self-resetting fuse.
Table 2.1 Typical Rate Update Times
Rates (Hz) Time Between Pulses (ms) Time Between Updates (ms)
1 to 59 17 to 1000 17 to 1000
60 to 1000 0 to 16 0 to 33
Above 1000 0 to 1 16
IMPORTANT
Because of the way the 1746-HSCE2 performs rate
value calculations, invalid rate measurements may
occur if the input frequency is below 60 Hz.
Therefore, we recommend that the 1746-HSCE2
module not be used for rate monitoring or rate range
control for frequencies below 60 Hz.
The invalid measurements apply only to rate values
and do not affect the count value reported to the
controller, which are always correct.