58
c
HAPTER
4:
Operation
Model 335 Temperature Controller
4.5.1.5 Heater Out Display
The heater output can be displayed in units of percent of full scale current or percent
of full scale power. The heater output display on the front panel is displayed in these
units, and the Manual Output parameter is set in these units. The availability of full
scale current and power is determined by the heater resistance, max current setting,
and heater range.
The heater output display is a calculated value intended to aid in system setup and tun-
ing. It is not a measured value, and may not accurately represent actual power in the
heater.
Menu Navigation:
Output Setup
Q
Output
(1 or 2)
Q
ENTER
Q
Heater Out Display
(Current or Power)
Default: Current
Interface Command:
HTRSET
4.5.1.6 Output Modes
You can configure the heater outputs in one of four output modes: Off, Closed Loop
PID, Zone, or Open Loop. The Off mode prevents current from being sourced to the
given output. Closed Loop PID is the mode most often used for controlling tempera-
ture. Zone mode builds on the Closed Loop mode by providing automatic changing of
control parameters on up to ten different temperature zones. Open Loop mode pro-
vides a means of applying a constant current to the output.
Menu Navigation:
Output Setup
Q
Output
(1
or
2)
Q
Output Mode
(Off, Closed Loop PID, Zone, Open Loop)
Default: Off
Interface Command:
OUTMODE
4.5.1.6.1 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 335. In this
mode the controller attempts to keep the load exactly at the setpoint temperature
you entered. To do this, it uses feedback from the control input sensor to calculate and
actively adjust the control output setting. The Model 335 uses a control algorithm
called PID that refers to the three terms used to tune the control. Refer to section
4.4.9 for details on assigning a Control Input for the closed loop feedback. Refer to
section 2.7 and section 2.8 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
Output
(1 or 2)
Q
Output Mode
(Closed Loop PID)
Interface:
OUTMODE
4.5.1.6.2 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 the settings are changed manually, the controller
will use the new setting while it is in the same zone and will update to the pro-
grammed zone table settings when the setpoint crosses into a new zone.
If desired, the control parameters can be changed manually, just like Closed Loop PID
mode, but they will be automatically updated once the setpoint crosses a zone boundary.
