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GL3NN

conveyor speed

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can any one help with a speed a conveyor is traveling using an encoder?  I have a 360 pulse per rev encoder that when measured in position counts 730 pulses per 1 rev of the conveyor roller. the speed of the conveyor changes daily by the operator and id like to see the speed displayed on the HMI i'm using a micrologix 1100 with built in HSC

id really appreciate any input off you wizards 

Edited by GL3NN

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please help

Edited by GL3NN

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While the MicroLogix timers are not extremely accurate (because they depend on the scan rate for evaluation), the MicroLogix does have a Selectable Timed Interrupt (STI) feature that triggers off the controller's internal clock pulse and executes a subroutine at that rate.  You can set the rate in 1 ms increments.    Look in the "Function Files" section of the controller organizer and in the User Manual for details about how the STI feature works.

The RA Knowledgebase includes a document (19445, Access Level = TechConnect) that describes using the STI and a High-Speed Counter to simply count the accumulated pulses between executions of the STI and calculate a rate in Hz or kHz, from which you could calculate your conveyor speed.

The only HSC-related instruction you really have to use is the Reset Accumulated Value (RAC).    Run it once at the first scan of the processor in your normal PLC program, and then run it at the end of the Program File that is jumped to by the STI interrupt.     That way the Accumulated Value in HSC:0.ACC will always be just the number of counts accumulated during the STI period (set in HSC:0.SPM).

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