[foxboro] RAMP block question

One of our specialists wanted me to put this question out on the list.
He has built a RAMP block that will be used to ramp the remote setpoint
of a PIDE block in a control scheme.  The RAMP is supposed to move 12000
SCF ( actually from 0 to 12 ) in 15 minutes.  He set the ramp rate at
0.8 or 12/15.  When he runs the block as stand alone, and times it, it
works great.  0.8 the first minute, 1.6 the second etc...  When he makes
the one necessary connection to the remote set point of the PIDE it
ramps twice as fast.  The actual output of the ramp is twice as fast
i.e. 1.6 in the first minute instead of 0.8.  Any ideas why?
P.S. KSCALE is set at 1.0, Range in and out is the same, scale is the
same, engineering units are the same.  Period and phase are even
matched.  Every block in compound are on 1 second period phase 0.  Only
5 blocks in the compound.  Version 6.3 system running display manager
and legacy historian.  When he adjusts the ramp rate to 0.4 or half it
ramps at the rate he wants but we want to know why.

Chad M. Airhart
Senior Engineer (Instrument, Electrical and Control Sys)
Lyondell Chemical Co.                             Victoria Plant
Ph. (361)572-2568
Fx. (361)572-2541
Cell. (361)935-3230


 
 
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