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Thermometers - General Information0 pages
Data sheet
INFO
THERMOMETER
Date
Page
10/2013
1 of 3
GENERAL INFORMATION ABOUT THERMOMETERS
INTRODUCTION
The name is referred generally to an instrument for the measurement of temperature, but in practice it is an instrument to
measure temperature changes by means of dimension variation (bimetal thermometer) or pressure variations (gas
expansion thermometer) or electric resistance variations (resistance thermometers) resulting from temperature changes.
GAS EXPANSION THERMOMETER. The measuring principle of these thermometers is based on pressure variations
caused by the expansion of a fluid or gas into a closed enclosure. The closed sensing element is made of a Bourdon tube
pressure gauge connected to the thermometric bulb containing the liquid or the captor gas through a flexible capillary.
Using a gas (Nitrogen or Helium), the temperature-volume-expansion is linear.
BIMETAL THERMOMTER. The bimetal temperature gauge relies on the difference between the thermal expansion of two
different metals which are welded at one end and laminated together in a wound cylindrical or flat spiral.
DEFINTIONS
THE BULB is the vessel containing the sensing element (liquid, gas, bimetal) and it is put into the heat source.
THE WELL is used to contain the bulb to protected it against corrosion, abrasion, bending and breakage and to separate
the process fluid from the ambient.
SPIRAL BOURDON SPRING is the indicator element able to pick up pressure variations caused by the thermal
expansion of intermediary fluid contained in the bulb.
FLEXING CAPILLARY TUBE is the transmission and connection element between bulb and spiral Bourbon tube. It is
used to read temperature remote from the heat source.
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PCI (Process System Solutions) Ltd, Unit 7 Slaidburn Crescent, Southport, Merseyside, PR9 9YF, UK,
Tel: +44 (0) 1704 509090, Fax: +44 (0) 1704 509091,
email: sales@pci-instruments.com, Website: www.pci-instruments.com
