Specifications

Synergy Nano Technical Manual, Revision -
Page 233
14.0 CASCADE TEMPERATURE CONTROL
Cascade is a control method that uses two control loops and sensors to provide better performance than can
be achieved with one loop. One control loop provides the setpoint for a second loop. With this method, the
product temperature reaches its setpoint more quickly than with single loop control, while minimizing
overshoot.
Single loop control compares the temperature of the discharge air of the conditioning section to a
temperature setpoint, and adjusts the heating / cooling systems accordingly.
In Cascade control the outer loop is dedicated to the unit-under-test. The inner loop controls the air
temperature. The outer loop monitors the unit-under-test temperature and compares it to the unit-under-test
setpoint. An error signal is generated and then adjusted by the PID set up for the outer loop. An output power
level signal is produced ranging from –100% to +100%, which is converted linearly to a temperature setpoint
using the set point low limit and set point high limit temperature settings. This temperature setpoint is sent to
the inner loop.
The inner loop monitors the discharge air from the conditioning system and compares it to the temperature
set point generated by the outer loop. An error signal is generated and then adjusted by the Heat and Cool
PIDs. An output power level signal ranging from 0 to 100% is produced and sent to the heating and cooling
systems.
Warning: Careful consideration should be paid to the Cascade Control setup since the chamber
air temperature will often go to these the limits. This will always occur if the product sensor isn’t
connected properly. A secondary limit controller set appropriately should always be used to
prevent damage to the chamber and/or to the unit-under-test (product) in the event of controller
or primary sensor failure. Cascade High Limit should be always be set to the maximum allowable
air temperature for the chamber and product.
Error
Signal
INNER LOOP (AIR)
OUTER LOOP
(UUT)
UUT, or RTD2
Temperature
UUT Setpoint
PID Set
Temperature
Setpoint
Air Temperature
RTD1
PID Set
Heating System
0 to 100 %
Cooling System
0 to 100 %
CASCADE CONTROL
Error
Signal
+
-
-
+
Power Level
-100% to +100%
Lo / Hi Limit
PID Set