Selecting the rate period parameter, Selecting the rate period parameter -13, Rate period - bits 0 to 7 (sequencer mode) – Rockwell Automation 1746-HSCE,D17466.5 High-Speed Counter Module User Manual
Page 31
Publication 1746-UM006B-EN-P - August 2005
Module Operation 2-13
Selecting the Rate Period Parameter
The Rate Period parameter defaults to 0 and must be set to a value
between 1 and 255 (10 ms to 2.55 seconds) to avoid a configuration
error. Consider the following when selecting the Rate Period:
•
Make sure your Rate Period does not allow a Rate Counter
Overflow to occur. This will depend on the maximum pulse
frequency and input type. For example if the maximum input
frequency is 10k Hz and the input type is X2 encoder:
Rate Period < 32767/(10000 x 2) = 1.63 seconds
The Rate Period should be set less than 1.63 seconds for this example.
•
A large Rate Period will introduce a delay in system response to
a rate change. If system response is critical keep the Rate Period
short. However, if system response is not critical, a longer Rate
Period will help filter the Rate Period measurement.
•
The shorter the Rate Period, the less accurate the resulting Rate
Measurement. The maximum error of the measurement can be
expressed as:
Maximum Error = 1/Rate Period
For example, if the Rate Period = 0.5 seconds, the resulting Rate
Measurement is accurate to within 2 Hz.
Rate Period - bits 0 to 7 (Range and Rate Mode)
Rate Period, Word 9
Bit Number (decimal)
Rate Period
15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
M0:e.9
Rate Period, Word 16
Bit Number (decimal)
Rate Period
15 14 13 12 11 10 9
8
7
6
5
4
3
2
1
0
M0:e.16
Rate Period - bits 0 to 7 (Sequencer Mode)