Owner manual

Appendix B: Enhanced Process Control
143
Cascade Control
The Cascade control feature allows the output percentage of one control
loop to influence the setpoint of a second control loop.
A loop designated as a Cascade output loop (primary loop) can still be
used for direct PID control of an output. A single loop can be either set
up as Cascade or Ratio control, but not both. The Cascade output loop is
assigned to another control loop (secondary loop), which performs the
actual control of the final control element.
Setting Up Cascade Control
In order to set up Cascade control, you need to configure these
variables:
1) Cascade output assignment. The control output (primary loop num-
ber) which will provide the output to the internal controller SP calcu-
lation for the secondary loop.
2) Base SP. The SP corresponding to 0% output (heat and cool) from the
primary loop. This value is expressed in the same engineering units
as the secondary loop PV, adjustable from the minimum reading to
the maximum reading.
3) Minimum SP. The lowest value of the secondary loop SP. The mini-
mum SP overrides any calculation caused by the primary loop calling
for a lower SP. This value is expressed in the same engineering units
as the secondary loop PV, adjustable from the minimum reading to
the maximum reading.
4) Maximum SP. The highest value of the secondary loop SP. The max-
imum SP overrides any calculation caused by the primary loop call-
ing for a higher SP. This value is expressed in the same engineering
units as the secondary loop PV, adjustable from the minimum reading
to the maximum reading.
5) Heat cascade span. The multiplier which is applied to the primary
loop heat output percentage. The default value = Maximum SP - Base
SP). The range is -9999 to +9999.
6) Cool cascade span. the multiplier which is applied to the primary
loop cool output percentage. The default value = Minimum SP -
Base SP). The range is -9999 to +9999.