Lake Shore Model 331 Temperature Controller User’s Manual
4.13 HEATER RANGE AND HEATER OFF
Heater output for Loop 1 is a well-regulated variable DC current source. The Heater output is optically
isolated from other circuits to reduce interference and ground loops. The Heater output for the main
control loop (Loop 1) can provide up to 50 W of continuous power to a resistive heater load and
includes two lower ranges for systems with less cooling power. Heater output is short-circuit protected
to prevent instrument damage if the heater load is accidentally shorted.
Loop 1 Full Scale Heater Power at Typical Resistance
Heater Resistance
Heater Range
Heater Power
10
Ω
Low
Med
High
100 mW
1 W
10 W
25
Ω
Low
Med
High
250 mW
2.5 W
25 W
50
Ω
Low
Med
High
500 mW
5 W
50 W
NOTE
: During normal operation, if the input type or input curve is changed for the control
input, the heater will automatically shut off.
A common error condition that may appear is “HTR Open.” This error message will appear when the
heater senses there is no load connected to the rear panel terminals. The user can correct this problem
by properly connecting a heater load. It could also indicate a malfunction internal to the Model 331,
such as a loose connection or a malfunctioning component, but this is much less likely. Other error
messages are summarized in Paragraph 8.8.
Specifications of heater output are provided in Paragraph 1.X – Instrument Specifications. Heater
theory of operation is provided in Paragraph 2.4 – Heater Selection and Installation. Various Heater
installation considerations are provided in Paragraph 3.7 – Heater Output Setup.
The Model 331S only has the additional ability to configure the analog output as a variable DC voltage
source capable of a 1 W output.
Once control setup parameters are configured (Paragraph 4.7), and the active control loop is selected
(Paragraph 4.6.1), the desired heater range is selected by pressing the
Heater Range
key.
Select for Loop 1 °®
Heater Range Off
Use the
s
or
t
key to cycle through Loop 1 Heater settings: Off, Low, Med, and High. Once the
desired heater setting is displayed, press the
Enter
key. You will return to the normal display.
For the Model 331S only, use the
s
or
t
key to toggle between Loop 2 Heater settings: Off and On.
Once the desired heater setting is displayed, press the
Enter
key. You will return to the normal display.
NOTE:
If the display shows Heater Disabled, the analog output does not have the proper
parameter configuration to work as a control loop. Refer to Paragraph 4.16.
To immediately turn the heater off, press the
Heater Off
key. If the Heater Range is not being displayed
on the front panel, the user should immediately press the
Heater Range
key to verify that the proper
loop is displayed and the heater shows Off.
Operation
4-25
