Isotech Libra 785 Specifications
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SOLUTIONS FOR PRIMARY & SECONDARY LABORATORIES
Stirred Liquid Baths
-65 to -80°C
785 Parallel Tube
g
Uncertainties to <1mK
g
Physical separation of heating from Calibration Volume
g
Three models covering -80 to 300°C
Isotech calibration baths employ sophisticated designs to
ensure calibration to the smallest of uncertainties. In 1986
Isotech purchased the interests of H N Irving & Sons
Temperature division which had specialised in providing high
quality baths to NPL and other international laboratories.
The knowledge and concepts from this scientific instrument
manufacturer were used in the development of the Isotech
815 and 915 Parallel Tube Liquid Baths. Whilst there is a
higher cost compared to simple designs the quality and
pedigree is unmatched.
The key feature is the physical separation of the chamber in
which the liquid is heated or cooled from the chamber that
contains the calibration volume in which the thermometers are
placed.
The geometry of parallel tube is also important, with the shape
and angle of the curves optimised for temperature uniformity.
The new Libra Model 785 achieves this with the same parallel
tube assembly as used in the 915 packaged into a different
case and now with internal refrigeration can be used to lower
temperatures.
The cooling power varies dynamically with the benefit of
giving greater stability at lower temperatures.
Model All Models 785L 785M 785H
Temp Range -80°C - 125°C -40°C - 125°C 30°C - 300°C
Volume 98mm Diameter, 485mm Deep
Absolute Stability ±0.0025°C ±0.006°C ±0.006°C ±0.006°C
Direct in Liquid (Water, 50°C) (Methanol, -80°C) (Methanol, -40°C) (C10 Oil, 125°C)
Vertical Uniformity From <1mK - See evaluation report
Heating time 25°C to 125°C < 50 mins (C10 Oil) 30°C to 250°C < 150 mins (VH Oil)
Cooling time 0°C to -80°C < 300 mins 10°C to -40°C < 180 mins (Methanol) (Methanol)
Display Resolution (Whole Range): 0.01°C 0.01°C 0.01°C
Liquid Height (Above Surface) 3mm 3mm 3mm
Design Parallel Tube: Separate Calibration and Mixing Chambers
Communications Includes Serial Interface, PC Cable and Software
Dimensions 485mm wide, 525mm deep, 1150mm high
Weight 78kg 68kg 48kg
Safety Compliant to CE Regulations
Power 2.8kW 1kW 800W
108-130 or 208-240V, 50/60Hz
Whilst the bath has a maximum immersion of 485mm the fluid
requirement is just 8.5 litres. This helps to lower operating
costs as many other baths require a much larger volume of
fluid, which in turn can be costly.
How to Order 785L 785M 785H
Refer to Evaluation Report for Full Details
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SOLUTIONS FOR PRIMARY & SECONDARY LABORATORIES
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785 Operation
1. The Liquid Flows Down into the
Mixing Chamber through an orifice
plate, the flow rate of which is
adjustable from the front panel.
2
. Cooling / Heating Chamber,
circular design for optimum flow
and uniformity.
3
. The calibration chamber is
separate from the cooling /
heating chamber.
4
. The Liquid flows over a weir a little
higher than the bath lid suiting
total immersion liquid in glass
thermometers.
5
. The Liquid flows into a large
volume liquid tray which caters for
the expansion of the liquid as it
is heated. The liquid re-circulates
around the bath.
6
. High Efficiency Thermal Insulation.
4
5
Liquid height
typically 3mm
above top
surface
1
Seperate
callibration
volume
2
3
Advanced parallel tube design
Lowest Comparison Calibration Uncertainties
Isotech best practise for comparison calibration of
resistance thermometers is to determine the resistance
of the thermometer under test by directly comparing it
to a Standard Platinum Resistance Thermometer.
The comparison is made using a thermometry bridge,
such as the microK, to measure the resistance ratio of
the two thermometers. An advantage of this approach
is that if both thermometers are of the same type both
will follow the same temperature fluctuations and the
resistance ratio will remain very stable. This method can
largely eliminate the effects of the bath stability, what
is needed is temperature uniformity in the calibration
volume, it needs to be isothermal.
The physical separation of the calibration chamber
from the heating and cooling chamber along with
the attention to the segments and contours provide
an isothermal volume that is superior to other baths.
The result a comparison bath providing the lowest
comparison calibration uncertainties, reflected in our
UKAS schedule.
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