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SOLUTIONS FOR PRIMARY & SECONDARY LABORATORIES
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Cryostat
Model 459
-80 to -180°C
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Extreme Low Temperature Calibration
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High Stability
When we considered low temperature comparison
calibration, we had to take into account Health and Safety
considerations, both of the liquids used in compressors to
generate low temperatures and also the liquids used in the
calibration volume itself. The cost of chillers increases
considerably for very low temperatures. We concluded that
using chillers for very low temperatures was expensive,
unsafe and unreliable.
Our solution is a simple heated metal block design using a
single, safe surrounding liquid, liquid nitrogen.
An apparatus immersed in liquid nitrogen will cool to
approximately -195°C. Our design, using a controller and
heater, permits the cryostat to be set at any temperature
above liquid nitrogen temperature.
The Cryostat comprises an insulated machined copper
equalizing block inside an 80mm diameter tube 480mm
long, attached via a flange to a lid giving access for three
thermometers, a vacuum port and a Lemo connector for
the temperature sensor and heater. A cable runs to a
controller which sets the temperature. An RS422 connector
permits the calibration to be automated using one of our
Software programs.
Evaluation
The most used range for the Isotech Cryostat is between
-80°C to -180°C. This temperature range is selected
because Oxygen condenses at -186°C and if this is then
accidentally boiled off it can cause a health and safety
issue. The performance of the Cryostat actually improves
as the temperature is lowered because the temperature
difference between Cryostat and it’s surrounding liquid
nitrogen is smaller. The measurements were made with
two model 670 thermometers.
Method
The Cryostat is connected to a vacuum pump. It is
pumped for five minutes and then sealed. The Cryostat
is connected to the controller, switched on to check the
connections. The Cryostat is then lowered into the
container of liquid nitrogen, which should come between
25mm and 75mm below the flange. Three thermometer
tubes exit the Cryostat and have nylon compression
fittings. The standard PRT and unknown thermometers
to be calibrated are lowered into the wells and the nylon
fittings are hand tightened until the nylon grips the
thermometer without damage. The controller is set to the
required temperature and the Cryostat left to stabilize
before comparison readings are made.
Model 459
Cryostat Temperature: -80°C to -180°C
Absolute Stability ±0.005°C at -80°C
(over 30 minutes)
±0.0015°C at -150°C
(as measured by one of the 670 thermometers in the bottom of one of
the pockets of the cryostat)
Homogeneity ±0.005°C
pocket to pocket
Vertical Profile ±0.005°C at -80°C
(over bottom 50mm)
±0.01°C at -150°C
Immersion Depth 560mm
Neck Diameter 120mm
Compatibility Liquid Nitrogen Containers
Nitrogen Capacity 35 litres
How to Order
459 Cryostat
Accessories
459-01-01 Hand Vacuum Pump
459-01-02 Electric Vacuum Pump
459-01-03 35 Litre Cryostat Container
459-01-04 25 Litre Container for topping up
Optional Container for Cryostat
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