Lake Shore Model 340 Temperature Controller User’s Manual
Temperature Control Operation
6-11
6.13 CONTROL OUTPUT LIMITS
Control limits were added to the Model 340 as added protection to prevent parameter settings that can
damage the cooling system.
6.13.1 Setpoint Limit
Setpoint temperature limit is a global limit for a control loop. Setpoint values above the limit are rejected and
the setpoint defaults to the limit value. The limit is entered in kelvin and works with setpoint units of kelvin or
Celsius. The limit does not work when sensor units are chosen for the setpoint.
The Model 340 turns off the control output if the temperature of the control sensor exceeds the global limit.
The global setpoint limit works along with the individual limits that can be entered in a temperature response
curve. The curve limits are only active when a sensor using that curve is chosen as a control sensor while the
global limit is active all the time. The lower of the two is used to limit the setpoint.
To change the setpoint temperature limit, press the
Control Setup
key. The control loop indicator is
highlighted in the upper left hand corner. Use the
s
or
t
key to select a control loop and press the
Enter
or
Next Setting
key. The control setup parameters for that loop appears on the screen. Press the
Next Setting
key until the setpoint field under the limits heading is highlighted. Use the number keys to enter the maximum
setpoint in kelvin. Press the
Enter
or
Next Setting
key to continue with more settings, or press the
Save
Screen
key to store the changes in the Model 340. The default setting is 475 K.
6.13.2 Control Output Slope Limit
Some experiments can not tolerate fast changes in control output. The slope limit feature keeps changes in
control output below a user specified rate of change. There is a different limit for rising and falling slope. The
rising slope limit is shown as +Slope, the falling slope limit is shown as -Slope. Both are set in percent of
output current per second. The setting range is 0 to 100 with a resolution of 0.1.
To change the output slope limit, press the
Control Setup
key. The control loop indicator is highlighted in the
upper left hand corner. Use the
s
or
t
key to select a control loop and press the
Enter
or
Next Setting
key.
The control setup parameters for that loop appear on the screen. Press the
Next Setting
key until the slope
field under the limits heading is highlighted. Use the number keys to enter the maximum slope in percent per
second. Press the
Enter
or
Next Setting
key to continue with more settings, or press the
Save Screen
key to
store the changes in the Model 340. The default setting is 0 (off).
6.13.3 Heater Range Limit
Accidental heater range settings are possible because the heater range can be set directly from the normal
display of the Model 340. A heater range limit feature is intended to prevent heater range settings that could
harm the control load. The heater range can be set to the user specified limit setting but not above. The range
limit is accessed through control setup operation so it can not be changed unintentionally. The range limit is
only available for the heater output on Loop 1. The full scale power of a given heater range depends on the
maximum current setting so the maximum current parameter should be set before the range limit.
To change the heater range limit, press the
Control Setup
key. The control loop indicator is highlighted in the
upper left hand corner. Use the
s
or
t
key to select a control Loop 1 and press the
Enter
or
Next Setting
key. The control setup parameters for that loop appear on the screen. Press the
Next Setting
key until the
range field under the limits heading is highlighted. Use the
s
or
t
key to select a range limit. Press the
Enter
or
Next Setting
key to continue with more settings, or press the
Save Screen
key to store the changes in the
Model 340. The default setting is the highest range.