leitmotif
Member
In another post
http://www.plctalk.net/qanda/showthread.php?t=2473
post #4
Ron Beaurford said
"And THAT - dear readers - is why I keep harping-harping-harping on maintaining that all important relationship between the PID’s internal “Loop Update Time” setting and the scheduling of the external “trigger” event. If those two settings are not kept in sync, then heaven help you - I can’t."
OK so you have two clocks controlling this - so they must be in synch -
QUESTION why not use only one clock ie loop update time
ANSWER (mine) process may have an interval where the PID must be put on hold to allow process to change ?? For example on AB SLC 5/05 am starting to learn how to use PID to control speed of a hydraulic motor by using VFD to vayr speeed of the hydraulic pump.
When motor reverses (using solenoid actuated 4 way valve)the tach generator output reverses. I have to (choose ?) to multiply this by -1 to correct it back to a positive value. SO I think I will have to use timer to allow for time of motor reversal tand the calculation.
Have I got this right??
Dan Bentler
http://www.plctalk.net/qanda/showthread.php?t=2473
post #4
Ron Beaurford said
"And THAT - dear readers - is why I keep harping-harping-harping on maintaining that all important relationship between the PID’s internal “Loop Update Time” setting and the scheduling of the external “trigger” event. If those two settings are not kept in sync, then heaven help you - I can’t."
OK so you have two clocks controlling this - so they must be in synch -
QUESTION why not use only one clock ie loop update time
ANSWER (mine) process may have an interval where the PID must be put on hold to allow process to change ?? For example on AB SLC 5/05 am starting to learn how to use PID to control speed of a hydraulic motor by using VFD to vayr speeed of the hydraulic pump.
When motor reverses (using solenoid actuated 4 way valve)the tach generator output reverses. I have to (choose ?) to multiply this by -1 to correct it back to a positive value. SO I think I will have to use timer to allow for time of motor reversal tand the calculation.
Have I got this right??
Dan Bentler