8 - Timers and counters - Fall 09

8 - Timers and counters - Fall 09 - MFET 243 Automated...

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Unformatted text preview: MFET 243, Automated Manufacturing I 10/5/2009 Timer and Counter Instructions 1 Timer and Counter Instructions Fall ‘09 T.E. Kostek MFET 243 MFET 243 Automated Manufacturing I Automated Manufacturing I Topics Introduction to timers and counters Introduction to timers and counters Timer and counter applications ControlLogix Timers 2 ControlLogix Counters MFET 243, Automated Manufacturing I 10/5/2009 Timer and Counter Instructions 2 Introduction to Timers and Counters Introduction to timers and counters Timers and counters Timers and counters: Are fundamental PLC instructions common to all PLCs Function like traditional hardwired timers and counters 4 counters Function as output instructions in a PLC program MFET 243, Automated Manufacturing I 10/5/2009 Timer and Counter Instructions 3 Introduction to timers and counters Timers and counters generate both word level Timers and counters generate both word level (DINT) and bit level (BOOL) data and status Bit level ( BOOL ) examples: Done (DN) bit Enable (EN) bi 5 Enable (EN) bit Word level ( DINTs ) examples: Accumulated (ACC) value Preset (PRE) value Timer and Counter Applications MFET 243, Automated Manufacturing I 10/5/2009 Timer and Counter Instructions 4 Timer Applications PLC timers often provide a necessary delay in operation while controlling a sequential machine routing pallets on a while controlling a sequential machine, routing pallets on a conveyor system, etc. With respect to a conveyor application, a timer could be used to cause an on-delay so that a pallet traveling down the conveyor settles into a desired position. After the delay, the pallet might be: Raised by a shot pin device into a fixed position 7 Clamped into a fixed position Pushed by a ram in order to loop the pallet around the end of a conveyor Continued on next slide Timer Applications Timers are used when event driven programming is not possible For instance, suppose a pneumatic cylinder does not have sensors which indicate when the cylinder is fully extended or fully retracted. In this time driven application, a timer could be 8 implemented such that the cylinder is extended for 5 seconds and then retracted back to its home position. Continued on next slide MFET 243, Automated Manufacturing I 10/5/2009 Timer and Counter Instructions 5 Timer Applications When event driven programming is implemented, a timer can be used to determine if an event fails to occur (i.e., Error Trapping). Example: Suppose a pneumatic cylinder has sensors which indicate when the cylinder is fully extended or fully retracted. When the PLCs output is switched on (in order to extend the cylinder) a timer is enabled and starts timing....
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This note was uploaded on 02/29/2012 for the course MFET 243 taught by Professor T.e.kostek during the Fall '09 term at Purdue.

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8 - Timers and counters - Fall 09 - MFET 243 Automated...

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