4.6.1 Heater Outputs
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Menu navigation:
Output Setup
Q
Sample Heater or Warm Up Heater
Q
Heater Out Display
Q
(Cur-
rent, Power)
Default: Current
Interface command:
HTRSET
4.6.1.4 Output Modes
Both heater outputs can be configured in one of four output modes: Off, Closed Loop
PID, Zone, or Open Loop. In addition, the warm-up heater can be configured into a
warm-up mode. The Off mode prevents current from being sourced to the given out-
put. Closed Loop PID is the mode most often used for controlling temperature. Zone
mode builds on the Closed Loop mode by providing automatic changing of control
parameters at up to ten different temperature zones. Open Loop mode provides a
means of applying a constant current to the output. Warm-up mode is intended to
help bring a system to room temperature in order to change samples. Refer to
section 5.3 for more information regarding warm up mode operation.
Menu navigation:
Output Setup
Q
Sample Heater
Q
Output Mode
Q
(Off, Closed Loop PID, Zone,
Open Loop)
Output Setup
Q
Warm Up Heater
Q
Output Mode
Q
(Off, Closed Loop PID, Zone, Open
Loop, Warm Up)
Default: Off
Interface command:
OUTMODE
4.6.1.4.1 Closed Loop PID Mode
The Closed Loop PID mode is the most commonly used closed loop control mode for
tightly controlling temperature using the heater outputs of the Model 372. In this
mode, the controller attempts to keep the load at exactly the user-entered setpoint
temperature. To do this, it uses feedback from the control input sensor to calculate
and actively adjust the control output setting.
The Model 372 uses a control algorithm called PID that refers to the three terms used
to tune the control. Refer to section 4.6.1.5.1 for details on assigning a control input
for the closed loop feedback. Refer to section 2.11.2 and section 2.11.3 for a detailed
discussion of PID control and manual tuning.
In Closed Loop PID mode, the controller will accept user-entered proportional, inte-
gral, and derivative parameters to provide 3-term PID control. Manual output can be
used during closed loop control to add to the calculated PID control output.
Menu navigation:
Output Setup
Q
Sample Heater
or
Warm Up Heater
Q
Output Mode
Q
Closed Loop PID
4.6.1.4.2 Zone Mode
Optimal control parameter values are often different at different temperatures
within a system. Once control parameter values have been chosen for each tempera-
ture range (or zone), the instrument will update the control settings each time the
setpoint crosses into a new zone.
If desired, the control parameters can be changed manually (identical to Closed Loop PID
mode), but they will be automatically updated once the setpoint crosses a zone boundary.