Calculating speed measurement from encoder pulses

Hello,

Could someone tell me code for calculating encoder pulses to speed measurement with S7 PLC? I have an encoder that gives 1000 pulses per revolution. I am not so sure how to check the rollover and make the difference. Also, how can I check the encoder pulses and if they are not moving anymore, set an output that they have stopped?

Thanks

PK

Not famillar with the S7, however there should be a bit/flag in the counter register that will tell you if the counter value is =, <, or > as compaired to the last scan. If not you can record the value of the current scan and then compair it to the next scan.

Rollover: If the count is increasing and suddenly the current count is less then the previous count = rollover.

Speed: Presuming theres a 1 second clock bit, you compare the the values at 1 second intervals (subtract the 1st recorded value from the current value). D/1000 * 60 = rpm.

Salam (hello)
after i saw ur request i think u will find some importants information in this link
http://support.automation.siemens.com/CH/llisapi.dll?filteron=on&csquery0=314+ifm&aktprim=0&extranet=standard&func=cslib.csinfo&lang=fr&nodeid0=10805065&objaction=csbrowse&objid=10805065&siteid=cseus&subtype=133300
that's is a document of 314 IFM this kind of PLCs ( IFM means PLC with an integral functions as hight frequence counter and INPUTs of Process Alarm and for positioning that last one can help you to command a Motor by a pulse coder )
i hope that document help you

good luck

hello

Hello,

Thanks for your input. I am using a 318-2 processor. I was also wondering where I could find some kind of speed measurement SFC and others that are not in the standard library for future reference.

Thanks

PK

this might help a bit

http://www.plctalk.net/qanda/showthread.php?t=30772

hi

If you are using FM350(6ES7 350-1AH03-0AE0,single channel) and have installed the CD which comes with it,you can use the all the blocks of project zEN23_FMx50-1 which can be found at "Sample Projects" of Simatic Manager.
Under Hardware configuration of the FM 350 select "A+B" for monitoring and select "RPM measurement" under operating modes.

Thanks

Hello,

Thanks for everyone's help with this issue. I finally figured out how to use the timed interrupt file for taking the actual pulses and subtracting the previous stored pulses and then converting it to the correct engineering units to show meters/min. I was not able to find any bits on the FM350 card that triggered when the counter value was higher, equal to or less than the previous count. I also did not find any selection for RPM measurement in the setup of the FM350 counter card. Regardless it works now so thanks for your help!

PK