Lake Shore Model 340 Temperature Controller User’s Manual
6-8
Temperature Control Operation
6.11 SETPOINT RAMPING
The Model 340 generates a smooth setpoint ramp when the setpoint units are expressed in temperature. The
user can set a ramp rate in degrees per minute with a range of 0 to 100 and a resolution of 0.1. Once the
ramp feature is turned on, its action is initiated by a setpoint change. When a new setpoint is entered, the
instrument changes the setpoint temperature from the old value to the new value at the ramp rate. A positive
ramp rate is always entered and it is used by the instrument for ramps up and down in temperature.
The ramping feature is useful by itself but it is even more powerful when used with other features. Setpoint
ramps are often used with zone control mode. As temperature is ramped through different temperature zones,
control parameters are automatically selected for best control. Ramps are initiated and status read back using
a computer interface. During computer controlled experiments, the instrument generates the setpoint ramp
while the computer is busy taking necessary data. AutoTune does not function during a setpoint ramp
because the ramp rate disguises the reaction of the cooling system and no valid tuning data can be taken.
To turn on the ramp feature and set a ramp rate, press the
Ramp
key. The
RAMP SETUP
screen is displayed
with the control loop indicator highlighted in the top left hand corner. Use the
s
or
t
key to select Loop 1 or
2. Press the
Enter
or
Next Setting
key. The ramp setup information for that loop appears on the screen.
Press the
Next Setting
key until the
Ramp
field is highlighted. Use the
s
or
t
key to turn the ramp feature
On. Press the
Next Setting
key to highlight the ramp rate field. Use the number keys to enter a ramp rate
value and press the
Save Screen
key to save the changes in the Model 340. The default setting is Off, 0.1.
To stop a ramp in progress, press the
Ramp
key. The
RAMP SETUP
screen is displayed with the control loop
indicator highlighted in the top left hand corner. Use the
s
or
t
key to select Loop 1 or 2. Press the
Enter
or
Next Setting
key. The ramp setup information for that loop appears on the screen. Press the
Next Setting
key until the
Ramp
field is highlighted. Use the
s
or
t
key to turn the ramp feature
OFF
. Press the
Save
Screen
key to stop the ramp. Another method to stop the ramp is to press the
Setpoint
key then immediately
press the
Enter
key.
6.12 CONTROL OUTPUT
The output from the PID control equation in Loop 1 is directed to the heater output. The control output from
Loop 2 can only be directed to Analog Output 2. This section discusses using the heater output and an
Analog Output as a control output.
6.12.1 Heater Output Parameter Settings and Heater Range
Some difficulties may be encountered when configuring the heater output for the first time. It may be difficult
to judge the amount of heater power needed to control a cooling system before it tested. Another problem is
that the heater output is a current source and not a “power” source. The Model 340 itself adds confusion with
the number of available heater ranges.
There are three things that determine the full scale power of a given heater setup: heater resistance,
maximum current parameter, and the heater range parameter. Some typical heater output powers are given
in Table 6-2 to illustrate how these variables affect heater power.
The resistive heater is not included with the instrument. The cooling system determines the physical size,
location, and resistance of the heater (refer to Paragraph 2.4). A heater must be chosen that can dissipate the
full scale power available on the highest heater range that may be used. It is recommended to use a heater
with resistance between 10
Ω
and 100
Ω
. The nominal resistance of the heater should be entered into the
instrument so the display shows heater parameters properly in power units. An incorrect setting of heater
resistance does not change the operation of the heater output.
To enter a heater resistance, press the
Control Setup
key and the
CONTROL SETUP
screen is displayed.
The control loop indicator is highlighted in the upper left hand corner. Use the
s
or
t
key to select Loop 1.
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
Htr
Ω
field is highlighted. Use the number keys to enter the resistance of the
heater in ohms. 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 25
Ω
.