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And, they can actually both be used on the same counter memory location. Consider the example in Figure 9.16, the example input I/1 drives the count-up instruction for counter C5:1. Input I/2 drives the count-down instruction for the same counter location. The preset value for a counter is stored in memory location C5:1 so both the count-up and count-down instruction must have the same preset. Input I/3 will reset the counter.
plc timers -9.16
Figure 9.16 A Counter Example
The timing diagram in Figure 9.16 illustrates the operation of the counter. If we assume that the value in the accumulator starts at 0, then the I/1 inputs cause it to count up to 3 where it turns the counter C5:1 on. It is then reset by input I/3 and the accumulator value goes to zero. Input I/1 then pulses again and causes the accumulator value to increase again, until it reaches a maximum of 5. Input I/2 then causes the accumulator value to decrease down below 3, and the counter turns off again. Input I/1 then causes it to increase, but input I/3 resets the accumulator back to zero again, and the pulses continue until 3 is reached near the end.
plc timers -9.17
The program in Figure 9.17 is used to remove 5 out of every 10 parts from a con veyor with a pneumatic cylinder. When the part is detected both counters will increase their values by 1. When the sixth part arrives the first counter will then be done, thereby allowing the pneumatic cylinder to actuate for any part after the fifth. BACK | NEXT Easy Access To All Pages 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140
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