Emerson Vission 20/20 Operation And Service Manual page 160

Appendix B • Vission 20/20 Application Procedures
SETPOINT SELECTION EXAMPLE
The following example is to illustrate the selection of setpoints for the Pulldown feature. The values picked are NOT
representative of actual fi eld applications.
Assumptions and Variables:
• Current suction pressure is at 80 psig
• Target suction pressure is 20 psig. (This defi nes a change of 60 psig).
• Time duration allowed to get to setpoint is 10 days (240 hours) of Pulldown time.
• Suction pressure change allowed for each step is 5 psig.
To calculate the Delay Per Step setpoint:
So, for the fi rst 20 hours the compressor runs at 75 psig, then for the next 20 hours at 70 psig, then for the next 20
hours at 65 psig, and so forth.
After the 12th step (running at 25 psig), 240 hours will have elapsed, and the new setpoint changes to 20 psig. After
the Pulldown setpoint equals or is less than the control setpoint, the Pulldown feature disables itself.
B - 4
Figure B-1. Pulldown Setpoints
Number of Pulldown Steps = Delta 60 psig change * 1 step/5 psig = 12 steps
Delay per step = 240 hours / 12 steps = 20 hours/step
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 2.0