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FX Series Programmable Controllers Devices in Detail 4
4-16
4.9.1 General timer operation
Timers operate by counting clock pulses (1, 10 and 100 msec). The timer output contact is
activated when the count data reaches the value set by the constant K. The overall duration or
elapsed time, for a timers operation cycle, is calculated by multiplying the present value by the
timer resolution, i.e.
A 10 msec timer with a present value of 567 has actually been operating for:
567
×
10 msec
567
×
0.01 sec = 5.67 seconds
Timers can either be set directly by using the constant K to specify the maximum duration or
indirectly by using the data stored in a data register (ex. D). For the indirect setting, data
registers which are battery backed/ latched are usually used; this ensures no loss of data
during power down situations. If however, the voltage of the battery used to perform the battery
backed service, reduces excessively, timer malfunctions may occur.
4.9.2 Selectable Timers
On certain programmable controllers, driving a special auxiliary coil redefines approximately
half of the 100 msec timers as 10 msec resolution timers. The following PLC’s and timers are
subject to this type of selection.
- For FX
1S, driving M8028 ON, timers T32 to 62 (31 points) are changed to 10 msec
resolution.
Driving special auxiliary coils:
• Please check the definition of special auxiliary coils before using them.
Not all PLC’s associate the same action to the same device.