Lake Shore Model 340 Temperature Controller User’s Manual
Temperature Control Operation 6-9
The maximum current parameter is included in the Model 340 to make it more compatible with existing
cooling systems. Even though this instrument is capable of sourcing two amps of heater current, there are
many control loads that will not tolerate that much current. Lower maximum current settings let the instrument
source less current without loosing heater ranges or resolution. Maximum current choices: 2 A, 1A, 0.5 A, and
0.25 A.
To select a maximum heater current, press the Control Setup key and the CONTROL SETUP screen is
displayed. Press the More key until the CONTROL LIMITS 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 Max Htr I (maximum heater current) field is highlighted. Use the s or t key to select from the list of
currents. Press the Enter key 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 1 A.
The Model 340 heater output
has five ranges. Each range
(below the highest range)
reduces the full scale heater
output power. The ranges are
spaced at approximate
decades in power. The heater
range setting is available from
the normal display so that it
can be changed easily during
an experiment. For example,
with the maximum current set
to 1 A and a heater resistance
of 25 Ω, the heater output
provides the full scale current
and power shown in Table 6-3.
The range is displayed as the
maximum power computed
with the maximum current
setting and user specified
resistance. If the power does
not change when you change
the range, the voltage
compliance is limiting the
maximum power. If ranges are
skipped, the heater range limit
is set.
To select a heater output
range, indicate Loop 1 by
pressing the Loop 1 key. The control parameters for that loop
appear in the lower portion of the display. Press the Heater Range key and the setting field for heater range
is highlighted. Use the s or t key to select a heater
range. Press the Enter key to save the change or the
Escape key to return to the previous setting. The
default setting is Off.
NOTE: The control output for Loop 1 must be
enabled before the heater can be turned on.
Refer to Paragraph 6.2.
The Model 340 has an immediate key operation for
turning the heater off. The Heater Off key is in a
prominent place on the keypad for easy access and it remains active when the keypad is locked. To turn off
the heater output, press the Heater Off key.
Table 6-2. Full Scale Heater Power at Typical Resistance
Heater Heater Maximum Current
Resistance Range 2 A 1 A 0.5 A 0.25 A
10 Ω
5
4
3
2
1
40 W
4 W
0.4 W
40 mW
4 mW
10 W
1 W
100 mW
10 mW
1 mW
2.5 W
250 mW
25 mW
2.5 mW
250 µW
625 mW
62.5 mW
6.25 mW
625 µW
62.5 µW
25 Ω
5
4
3
2
1
100 W *
10 W
1 W
100 mW
10 mW
25 W
2.5 W
250 mW
25 mW
2.5 mW
6.25 W
625 mW
62.5 mW
6.25 mW
625 µW
1.56 W
156 mW
15.6 mW
1.56 mW
156 µW
35 Ω
5
4
3
2
1
71.4 W
†
14 W
1.4 W
140 mW
14 mW
35 W
3.5 W
350 mW
35 mW
3.5 W
8.75 W
875 mW
87.5 mW
8.75 mW
875 µW
2.19 W
219 mW
21.9 mW
2.19 mW
219 µW
50 Ω
5
4
3
2
1
50 W
†
20 W
2 W
200 mW
20 mW
50 W
5 W
500 mW
50 mW
5 mW
12.5 W
1.25 W
125 mW
12.5 mW
1.25 mW
3.12 W
312 mW
31.2 mW
3.12 mW
312 µW
* Maximum power available.
†
Power limited by voltage compliance.
Table 6-3. Example of Max. Current Settings
Range Current Power
5 1 A 25 W
4 316 mA 2.5 W
3 100 mA 250 mW
2 31.6 mA 25 mW
1 10 mA 2.5 mW
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