Emerson 818-9010, Installation And Operation Manual

Page: 31 / 56

Figure 6-1
- Setpoint Estimates for Temp Readings
• 25
In Transcritical mode, there is a separate PID running.
To ensure there is a smooth transition between the subcrit-
ical PID and the Transcritical PID, there is a linear-ratio
transition algorithm between the two PID's output. This
linear-ratio algorithm transition will keep the valve open
and allow the Transcritical PID to ramp up and take over.
The transition time is adjustable by the parameter
"Trans_Time" if the valve tends to modulate too fast
during the transition. By increasing the "Trans_Time"
parameter, this will slow the transitions and allow less
modulation. The same function will happen when transi-
tioning from Transcritical mode to Subcritical mode as
well.
The Transcritical inputs, outputs, setpoint and PID parameters are listed below.
Table 6-4 - Transcritical Inputs
Inputs Description Type
Temperature - 1(T1)
Active Outlet Gas Cooler
Temperature
NTC Temperature
Temperature - 2 (T1)
Active Bypass Gas Cooler
Temperature
NTC Temperature
Pressure - 1 (P1) Active Outlet Gas Cooler Pressure 0-5VDC only
Control Temp Selector (CTS)
Enables T2 as Active Gas Cooler
Temperature if present
Digital Input