GSE 60 SERIES Technical Reference Manual page 457

Table 12-3: Frequency Measurement Method 'A' Output Based on Clock Source
Clock Frequency
Clock Period
Minimum
Measurement Period
Resolution of
Measured Frequency
using Period Listed
Above
Typical Measurement
Period
Resolution of
Measured Frequency
using Period Listed
Above
Maximum
Measurement Period
Resolution of
Measured Frequency
using Period Listed
Above
Maximum Input
Frequency using
Period Listed Above
The general restrictions listed in Table 12-3 can be attributed to the
following facts:
•
The maximum measurement period is 32,768 clocks.
•
The function can only count complete pulses (i.e. periods). As an
example, a change of one pulse in a 100 ms period results in a
frequency change of 10 Hz. (i.e. 1 pulse in 100 ms = 10 Hz, 2 pulses
= 20 Hz, etc...).
•
The maximum number of pulses that may be counted in one
measurement period is 65,535. Therefore, the period should not be
set longer than the time required for 65,535 pulses to occur at the
maximum expected frequency. This should not be a concern in most
applications.
As shown in Table 12-3, most applications should work well with
'Clock A' specified and a long measurement period. A period of 16.67
ms will result in the frequency being calculated at about the same rate
as the weight is re-calculated, i.e. about 60 Hz.
•
P858: "Edge": Specifies whether a rising or falling edge is used as
the reference edge for counting pulses. For most applications the
setting for this parameter will not have any noticeable effect.
However, if pulses are occurring sporadically and infrequently it may
become desirable to detect a specific edge, either rising or falling.
Programmable Digital I/O 12-11
Clock A Clock B
65,536 524,288
Hz Hz
15.26 µs 1.91 µs
0.015 ms 0.0019
ms
±65 kHz ±524 kHz
100 ms 10 ms
±10 Hz ±100 Hz
500 ms 62.5 ms
±2 Hz ±16 Hz
131,070 1024 kHz
Hz
60 Series Technical Reference Manual