Technical information

Mechanical temperature measuring instruments
WIKA data sheet IN 00.07

Temperature is an indicator of the thermal condition of a homogenous material or body. It expresses the energy of motion thatis contained in the molecules of the material. Transmission of temperature from one body to another, e.g. process medium
and thermometric sensor, requires close physical contact between both bodies to achieve thermal equilibrium. Conventionaltemperature measurement is based on the property of certain materials to alter their physical shape or volume proportional to
the temperature applied. The most commonly used principles in the WIKA production are highlighted below.

Bimetal thermometers
Operating principle
The temperature is measured by means of a bimetal system
inside the temperature sensor. The bimetal is made from two
metal strips, permanently joined together, each metal having
a different thermal expansion coefficient. This causes thestrip to deflect in proportion to the temperature variation. The
actual bimetal system consists of a bimetal strip that is either■■ helically or■■ spirally

change the shaft and pointer connected to the tube rotateand the temperature value is indicated on the scale. With
capillary lengths available between 500 and 10,000 mm, it isalso possible to measure temperatures at remote measuring
points.
WIKA expansion thermometers are available for temperature
ranges from -40 to +400 °C with accuracies complying withClass 1 and 2 of EN 13190.

Gas actuated thermometerwith or without capillary
Operating principle
Gas actuated thermometers consist of a stem, a capillary
and a case containing the bourdon tube element. These
components are connected to form a single system. The
complete measuring system is filled with an inert gas underpressure. Any temperature variation causes a change in theinternal pressure of the stem, leading to a deflection of thebourdon tube. A mechanical linkage (movement) transmits
this deflection to the pointer.

wound, depending on the size of the sensor and the temperature range to be measured. Any temperature variation
causes the bimetal to rotate an attached spindle.
This rotation is indicated by a pointer on a dial scale.
WIKA bimetal thermometers are available for temperature
ranges from -70 to +600 °C with accuracies complying withClass 1 and 2 of EN 13190.

Expansion thermometers
Operating principle
The temperature is measured by a liquid-filled measuringsystem consisting of a temperature probe, a capillary anda bourdon tube. These three components form a sealedsystem. Any temperature variation causes a change in theinternal pressure of this system. As a result of this pressure
WIKA data sheet IN 00.07 ∙ 04/2011

Variations in the ambient temperature acting on the case arecompensated for by a bimetal element mounted between themovement and the bourdon tube.
WIKA gas actuated thermometers are available for temperature ranges from -200 to +700 °C with an accuracy complying
with Class 1 of EN 13190.
Page 1 of 2

Conversion reference
How toFromK°C°F°R°RéKx

K= °C + 273.15

K= 5/9 (°F + 459.67)

K= 5/9 °R

K= 5/4 °Ré + 273.15°C°C= K - 273.15

x°C= 5/9 (°F - 32)°C= 5/9 °R - 273.15°C= 5/4 °Ré°F°F= 9/5 K - 459.67°F= 9/5 °C + 32x°F= °R - 459.67°F= 9/4 °Ré + 32°R°R= 9/5 K°R= 9/5 °C + 491.68°R= °F + 459.67

x°R= 9/4 °Ré + 491.68°Ré°Ré= 4/5 K - 218.52°Ré= 4/5 °C°Ré= 4/9 (°F - 32)°Ré= 4/9 °R - 218.52

xcalculate

Limit of error in °C

per DIN EN 13190
Applicable for expansion and bimetal dial thermometers
Scale rangein °C

Measuring
range in °C

Limit of error in ± °C
Class 1

Class 2-20 ... +40-10 ... +30

1-20 ... +60-10 ... +50-30 ... +30-20 ... +20-30 ... +70-20 ... +60-40 ... +60-30 ... +50

0 ... 60

10 ... 50

0 ... 100

10 ... 900 ... 160

20 ... 140

0 ... 250

30 ... 220

0 ... 400

50 ... 350

0 ... 600

100 ... 500

50 ... 650

150 ... 550-20 ... +120

-10 ... +110

-30 ... +50-20 ... +40-40 ... +40-30 ... +30-100 ... +60-80 ... +40

0 ... 80

10 ... 70

0 ... 120

10 ... 110

0 ... 200

20 ... 180

0 ... 300

30 ... 270

0 ... 500

50 ... 450

0 ... 700

100 ... 600

100 ... 700

200 ... 600

12
11
1
1
12
1
1
12
2
2

2.5
5
55

10
10
1010

Basic points of thermo-dynamic temperature scales
Unit

SymbolReference value
absolutezero

triple point ofwater2KelvinK

0273.16

4

Grad Fahrenheit°F-459.67

32.01

2

Grad Réaumur°Ré2

Grad Celcius°C

2

Grad Rankine°R-273.15
0-218.52

0.01

491.6802224222444510101015151515© 2008 WIKA Alexander Wiegand SE & Co. KG, all rights reserved.
The specifications given in this document represent the state of engineering at the time of publishing.
We reserve the right to make modifications to the specifications and materials.

WIKA data sheet IN 00.07 ∙ 04/2011
04/2011 GBPage 2 of 2WIKA Alexander Wiegand SE & Co. KG
Alexander-Wiegand-Straße 30
63911 Klingenberg/Germany
Tel.
(+49) 9372/132-0
Fax(+49) 9372/132-406
E-mail info@wika.de
www.wika.de