Open Loop Mode; Control Parameters; Control Input - Lakeshore 335 User Manual

4.5.1 Heater Outputs 59
The control algorithm used for each zone is identical to that used in Closed Loop PID
mode. The Zone feature is useful by itself, but it is even more powerful when used
with other features. We recommend using zone mode with setpoint ramping (section
4.5.1.7.7). Refer to section 5.3 for details on setting up zones. Refer to section 2.7 for a
detailed discussion of PID control.
Menu Navigation:
Output SetupQOutput (1 or 2)QOutput Mode (Zone)
Interface: OUTMODE

4.5.1.6.3 Open Loop Mode

Open Loop output mode allows you to directly set the output using only the
Manual Output and Range parameters. This guarantees constant current to the load,
but it does not actively control temperature. Any change in the characteristics of the
load will cause a change in temperature.
Any output can be configured to Open Loop mode. When an output is configured in
this mode, the Manual Output and Heater Range parameters become available in the
Output Setup menu for setting the output. For convenience, the Control Input param-
eter can be used to assign a sensor input, which then allows the output to be dis-
played on the front panel when using that sensor input's display mode. When
displayed on the front panel, the Manual Output and Heater Range direct operation
keys can be used for one touch access to these settings. Refer to section 4.3.1 for
details on configuring display modes.
Since there is no sensor feedback in open loop mode, there is nothing to prevent the sys-
tem from being overheated. We recommend using the Temperature Limit feature to help
protect the system from overheating. Refer to section 4.4.10 for temperature limits.
Menu Navigation:
Output SetupQOutput (1 or 2)QOutput Mode (Open Loop)
Interface: OUTMODE

4.5.1.7 Control Parameters

Once the output mode is chosen, the control parameters can be used to begin con-
trolling temperature. Control Input is used to create a control loop. The P, I, and D
parameters provide fine tuning of the control algorithm. Manual Output provides a
baseline output power about which to control. Setpoint is used to set the desired tar-
get temperature, and Heater Range is used to turn on the control output, as well as to
set the power range of the output. These parameters are described in detail in section
4.5.1.7.1 to section 4.5.1.7.8.

4.5.1.7.1 Control Input

For closed loop control (Closed Loop PID, Zone, Warm Up Supply), a control loop must
be created. A control loop consists of a control output for controlling the temperature,
and an input for feedback into the control algorithm. Use the Control Input parame-
ter to assign the control input sensor to the desired output.
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