Chapter 16 PLC Function ApplicationsMH300
16-9 Count Function Using Pulse Input
16-9-1 High-speed count function
The M
H300’s MI7 supports one-way pulse counting, or you can use MI6+MI7 to support AB-phase
two-way pulse counting, with a maximum speed of 33 k. The starting method is very simple, and only
requires setting M1038 to begin counting. The 32 bit count value is stored in D1054 and D1055 in
non-numerical form. M1039 resets the count value to 0.
Take MI7 one-way pulse input as an example:
NO
TE: When the PLC program defines MI7 for use as a high-speed counter, that is when M1038 or
M1039 is written in PLC procedures, the other functions of MI7 are disabled.
16-9-2 Frequency calculation function
Apar
t from high-speed counting, the MH300’s MI7 (one-way pulse counting) or MI6+MI7 (AB-phase
two-way pulse counting) can also convert a received pulse to a frequency. The following figure shows
that there is no conflict between frequency conversion and count calculations, which the MH300 can
perform simultaneously.
PLC speed calculation formula
D1057 Speed
D1058 Interval between calculations
D1059 Decimal places
Assume that there are five input pulses each second, (see figure below) we set D1058 = 1000 ms =
1.0 seconds as the calculation interval. This enables five pulses to be sent to the drive each second.
Assu
me that each five pulses correspond to 1 Hz, we set D1057 = 5.
Setting D1059 = 2 displays numbers to two decimal places, which is also 1.00 Hz. The numerical
value displayed at D1056 is 100. For simplicity, the D1059 conversion formula can be expressed in
the following formula:
D1056 = (Pulses per second / D1057) * (1000 / D1058) * (10^D1059)
Current count value
of MI8(H word)
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