Capacity Load/Unload Timers - Emerson Vilter Vission 20/20 Operation And Service Manual

Section 10 • Compressor Sequencing
Unload Rate 2 Offset (outer):
• Defi nes the outer Pressure/Temp setpoint offset
to monitor compressor load. If Suction Pressure/
Process Temperature drops below Unload Rate 1
offset and goes below Unload Rate 2 setpoint offset,
then sequencing decisions are made according to
Unload Rate 2 timer.

Capacity Load/Unload Timers

One of the following Capacity Load/Unload rate tim-
ers are used to make sequencing decisions periodically.
Suction Pressure/Process Temperature setpoints are
monitored to identify which one of the following timers
to be used.
Load Rate 1 (Inner):
• If Suction Pressure/Process Temperature goes be-
yond Load Rate 1 setpoint offset then Load Rate 1
timer is used to make periodic sequencing decisions.
10 – 2
Figure 10-2. Compressor Sequencing Screen - Page 2
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 1.9
Load Rate 2 (Outer):
• If Suction Pressure/Process Temperature surpasses
Load Rate 1 offset and goes beyond Load Rate 2 set-
point offset then Load Rate 2 timer is used to make
periodic sequencing decisions.
Unload Rate 1 (Inner):
• If Suction Pressure/Process Temperature goes below
Unload Rate 1 setpoint offset then Unload Rate 1
timer is used to make periodic sequencing decisions.
Unload Rate 2 (Outer):
• If Suction Pressure/Process Temperature surpasses
Unload Rate 1 offset and goes below Unload Rate 2
setpoint offset then Unload Rate 2 timer is used to
make periodic sequencing decisions.