Sometimes it necessary and need of time to monitor PLC scan time in PLC program, so for such situations there are some special register (D) in Delta PLC which help in performing such tasks. D1000 is such a special register which is used for monitoring PLC scan time. When the scan time exceeds the set time in the monitor timer, the red ERROR LED indicator remains shining and all outputs will be “Off”. Subscribe to Automation-Talk by Email.
The initial set value of the time in the monitor timer is 200ms. If the Delta program is long or the operation is too complicated, MOV instruction can be used for changing the set value as shown in above image. The maximum set value in the monitor timer is 32,767ms. Users can add WDT instruction (API 07) into PLC program.
When CPU execution progresses to WDT instruction, the internal monitor timer is cleared as 0 and the scan time will not exceed the set value in the monitor timer. There is one more special register D1039 which is for Fixed Scan Time and will be discusses later.
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nice information
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