As long as you provide a clock signal as a counter counting input signal, counter can achieve timing function, clock signal multiplied by the cycle counter value is time. Clock signal can be generated by the PLC internal special relay (such as the FX series PLC, M8011, M8012, M8013 and M8014), can also be generated by pulse, can also be generated by the PLC external clock circuit.
As shown in Figure 5-11 to counter implementation delay program, produced by the M8012 cycle of 0.1s clock pulses. When you start signal X15 is closed, M2 and lock, M8012 clock pulse counting inputs added to C0. When C0 amounted to 18,000 pulse, counter C0 C0 normally open contact closure, Y5 coils connected, Y5–contact action. From X15 close to Y5 delay time for 18000×0.1=1800s. Delay error and precision of the clock signal in cycles, to improve the timing accuracy, shorter clock must be used as a count signal.
Figure 5-11 a delay of the counter program
A) ladder diagram b) sequence diagram SHAPE \* MERGEFORMAT
Delay the program counter of the maximum delay time max count values and clock cycle limit, as shown in Figure 5-11 counter C0 max count values to 32767, so the maximum delay time is: 32767×0.1=3276.7s. To increase the delay time, you can increase the clock cycle, but which makes timing accuracy. To obtain a longer delay and at the same time ensure timing accuracy can be used to cascade two or more grade counter count. As shown in Figure 5-12 to introduce a two-tier counters count delay a cascade example. Diagrams composed of C0 a 1800s (30min) of the timer, the normally open every 30min closing a scanning cycle. This is because the reset input in parallel a C0 C0 normally open contact when C0 amounted to 18,000 pulse, counter C0 C0 normally open contact closure, C0 reset, C0 counter moves after a scan cycle began to count, C0 a cycle is 30min the clock pulse, pulse width for a scanning cycle. Another normally open as C0 C1 count input when C0 normally open connecting C1 enter a pulse, when total C1 counts pulses to 10, the counter C1, C1 normally open contact closure, Y5 coils connected, Y5–contact action. From X15 close to Y5, the delay time is 18000×0.1×10=18000s (5h). After counter is C0 and C1 series, maximum delay time is up: 32767×0.1x32767s=29824.34 h=1242.68 days.
5-12 delay of two counters of application programs