4.5.1 Heater Outputs
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4.5.1.3 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. Available full scale cur-
rent and power are 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, 2)
Q
Heater Out Display
Q
(Current or Power)
Default: Current
Interface Command:
HTRSET
4.5.1.4 Output Modes
The heater outputs can be configured 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 at up to ten different temperature zones. Open Loop mode pro-
vides a means of applying a constant current (or voltage for outoputs 3 and 4)to the
output.
Menu Navigation:
Output Setup
Q
Output
(1, 2, 3, or 4)
Q
Output Mode
Q
(Off, Closed Loop PID, Zone,
Open Loop)
Default: Off
Interface Command:
OUTMODE
4.5.1.4.1 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 350. 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 350 uses a control algo-
rithm called PID that refers to the three terms used to tune the control. Refer to sec-
tion 4.4.10 for details on assigning a Control Input for the closed loop feedback. Refer
to section 2.13 and section 2.14 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, 2, 3, or 4)
Q
Output Mode
Q
Closed Loop PID
4.5.1.4.2 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.
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