Omron SYSMAC CJ - REFERENCE MANUAL 08-2008 Reference Manual page 913

High-speed Counter/Pulse Output Instructions
Frequency Ranges
Value of P
0000 or 0001 hex
(Reading the frequency
of pulse output 0 or 1)
0010 hex
(Reading the frequency
of high-speed counter 0)
Pulse Frequency Calculation Methods
When the CPU Unit is a CJ1M CPU Unit with version number 3.0 or later,
there are two ways to calculate the frequency of pulses output from pulse out-
put 0 or 1 or pulses input to high-speed counter 0.
1. Standard Calculation Method (Earlier Method)
The count is calculated by counting each pulse regardless of the frequen-
cy. At high frequencies, the rising or falling edges of some pulses will be
corrupted, resulting in errors (roughly 1% error max. at 100 kHz).
2. High-frequency Calculation Method
In this case, the counting method is switched at high and low frequencies.
• High-frequency counting
At high frequencies (above 1 kHz), the function counts the number of
pulses within a fixed interval (the sampling time) and calculates the fre-
quency from that count. One of the following three sampling times can
be selected by setting the rightmost two digits of C.
Sampling time
10 ms
100 ms
1 s
• Low-frequency counting
At frequencies below 1 kHz, the Standard Calculation Method is used,
regardless of the sampling time setting.
Conversion result
0000 0000 to 0001 86A0 hex (0 to 100,000)
Counter input method: Any input method other than 4
differential phase mode
Result = 00000000 to 000186A0 hex (0 to 100,000)
Note If a frequency higher than 100 kHz has been input,
the output will remain at the maximum value of
000186A0 hex.
Counter input method: 4 differential phase mode
Result = 00000000 to 00030D40 hex (0 to 200,000)
Note If a frequency higher than 200 kHz has been input,
the output will remain at the maximum value of
00030D40 hex.
Value of C
0013 hex Counts the number of pulses every 10 ms.
The error is 10% max. at 1 kHz.
0023 hex Counts the number of pulses every 100 ms.
The error is 1% max. at 1 kHz.
0033 hex Counts the number of pulses every 1 s. The
error is 0.1% max. at 1 kHz.
Section 3-21
Description
873