Lake Shore 372, Руководство пользователя, Страница: 18 / 214

6 c
HAPTER
1: Introduction
Model 372 AC Resistance Bridge and Temperature Controller
1.4.2 Multiple Heater
Options Three separate heater outputs are available on the Model 372:
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Sample heater —for fine control of the sample stage at ultra-low temperatures
with up to 1 W of power available.
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Warm-up heater —supplying up to 10 W of power and featuring a warm-up mode
specifically for the purpose of bringing the system temperature up to allow work
to be performed on the sample stage.
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Still heater —an additional 1 W heater is available for the purpose of controlling
the temperature of a dilution refrigerator’s still. Alternatively, this output can
provide an analog out signal to other devices if required.
The sample and warm-up heaters have many powerful control options, including PID
control that allows both the setting of fixed temperature setpoints as well as ramp
rates.
1.4.3 Stable
Temperature Control When operating at ultra-low temperatures, even small amounts of added energy can
cause unwanted spikes in system temperature. The Model 372 heater outputs imple-
ment several protection mechanisms to reduce or eliminate this potential:
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The circuitry for the sample and still heaters are electrically isolated from other
instrument sections
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Multiple power range settings allow extremely fine or coarse power transitions,
depending on the need
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Heater outputs are shunted during power up and power range changes,
eliminating the potential for unwanted power surges
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Terminal connections allow twisted pair cabling to be easily used for heater wir-
ing; additional shielding of these wires can also be added to further reduce the
potential of injecting noise into a system via the heater cabling
1.4.4 Temperature
Zone Control Thermal response characteristics of a dilution refrigerator system can change quite
dramatically over the useful range of operation, particularly down towards the lower
temperature limit of a system, where cooling power is reduced. To accommodate
these system variations, different PID values can be set for different temperature
ranges (zones). This allows for more aggressive transition settings to be used at
higher temperatures where system response is faster, and less reactive settings at
low temperatures when temperature overshoots result in long recovery times.
FIGURE 1-8 Physical heater connections