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The tSTAT320 is a temperature controller for the liquid
helium and liquid nitrogen cryostats. It is used mainly with the combi cryostats
of the OptCRYO series and with variable temperature cryostat-inserts for
superconducting magnets of the CryoMagn series. Technical parameters of the
regulation procedure are quoted in the tables for optical cryostat.
The tSTAT320 regulates the sample temperature in the range
from 4.2 K up to room temperature. The electronic unit controls the power of the
electrical heater at the sample holder as well as the needle valve opening in
the gas-flow regulator included in the cryostat set of the optCRYO series. The
controller unit also has an integrated level gauge for liquid helium.
For temperature measurements a Cu:Cu(Fe) thermocouple is
used. The Cu:Cu(Fe) thermocouple, combined from the pure metal and doped metal
wires, provides large thermoelectric coefficient (>10 µV/K) at low
temperatures. In order to increase the precision of the temperature measurements
at low temperature the reference thermocouple is placed inside the cryogenic
reservoir (i.e. inside the He tank). The second thermocouple is placed near the
sample at the sample holder.
The controller unit tSTAT320 has a remote control
capability via a serial RS-232 interface. You can control the unit and obtain
the actual status and settings by simple plain text commands. This gives you an
opportunity to use the cryostat in a computer-controlled measurements.
The thermocouple can be replaced by a thermal resistor
calibrated using the precise temperature standard.
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T-couple connector
The connector for the thermocouple and level gauge is
located on the front side of the controller for easy access during standard
operation.
How the temperature controller works
The set value of the temperature can be given either in µV
or directly in Kelvin. It can be set manually with the keys on the control panel
or remote via the serial RS-232 interface.
How the level gauge works
The nitrogen level sensor is a rod, which is put into the
nitrogen reservoir. At the lower end of the rod there is a temperature sensitive
resistant (NTC) and another one is located close to the lower end of the rod. If
an NTC is dipped into liquid nitrogen its resistance increases drastically. This
effect is used to determine the filling level of the nitrogen
reservoir.
For the liquid helium sensor there is a superconducting wire inside the
sensor rod. That part of the wire, which is surrounded by liquid nitrogen, is in
the superconducting state whereas the remaining part of the wire is in the
normal conducting state. Hence, the total resistance of the wire is a measure
for the level of the liquid
helium.
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