Sensor class

Dependent on the process temperature different thermocouples are applied.

 

 Dependent on the process temperature different types of thermodouples (e.g. normally K or J) are applied. The thermocouple can be found in the measurement insert. The measurement accuracy is dependent on a number of different factors:

  • Sensor measurement accuracy: Thermocouple type, Classification (see detailed description below)
  • Thermocable measurement accuracy, compensation cable (see detailed description below)
  • Transmitter measurement accuracy: Accuracy, transmitter connection (for specification see Configurator)
  • Measurement point installation: Sensor installation (medium flow direction, minimum immersion length: 8x thermometer diameter on sheathed thermocouples, installation angle)

 

  

Thermocouple type:

According to the DIN EN 60584 these are divided into precious and non-precious thermocouples. Non-precious thermocouples such as E, J, K, N and T are more economical and used for temperatures up to 1100 °C. Precious thermocouples such as B, R and S are costlier and suitable for temperatures up to 1820 °C.

 

 

Type

Thermocouple

Temperature range

T

Cu / CuNi

-270...+400 °C

J

Fe / CuNi

-210...+1200 °C

E

NiCr / CuNi

-270...+1000 °C

K

NiCr / NiAl

-270...+1372 °C

N

NiCrSi / NiSi

-200...+1200 °C

R

Pt13Rh / Pt

-50...+1768 °C

S

Pt10Rh / Pt

-50...+1768 °C

B

Pt30Rh / Pt6Rh

0...+1820 °C

   
Grounded measurement points using sheathed thermocouples
   

Features

  • Short response time
  • Changed corrosion conditions due to the welding of the thermocouple to the sheath material

The thermocouple is pressed into a highly compressed ceramic mass (magnesiumoxide powder MgO).

Advantages:
- Higher temperature resistance
- Shock and vibration resistant
- High bendability (highly flexible at limited installation points)

  

 

 

  

Non-grounded measurement points using sheathed thermocouples
   

Features:

  • Longer response times
  • Interferance resistant
  • Higher temperatures

The thermocouple is pressed into a highly compressed ceramic mass (magnesiumoxide powder MgO).

Advantages:
- Higher temperature resistance
- Shock and vibration resistant
- High bendability (highly flexible at limited installation points)

 

 

  

Non-grounded measurement point with ceramic insulationfor high temperature thermocouples
   

Due to the ceramic insulation the thermo legs and the measurement point are protected and insulated from each other. This means that the stability of the measurement insert can be guaranteed.

   

Accuracy classifications:

  

Measurement accuracy of a sensor:
The DIN EN 60584 standard lays down the standard values and tolerances for the thermocouple combination used.

  

 

Type

Standard tolerance
(DIN EN 60584-2)

Reduced tolerance
(DIN EN 60584-2)

 

class

tolerance

class

tolerance

Thermocouples from non precious metals

T
(Cu-CuNi)

2

+/-1,0 °C (-40...133 °C)
+/-0,0075|t| (133...350 °C)

1

+/-0,5 °C (-40...125 °C)
+/-0,004|t| (125...350 °C)

J
(Fe-CuNi)

2

+/-2,5 °C (-40...333 °C)
+/-0,0075|t| (333...750 °C)

1

+/-1,5 °C (-40...375 °C)
+/-0,004|t| (375...750 °C)

E
(NiCr-CuNi)

2

+/-2,5 °C (-40...333 °C)
+/-0,0075|t| (333...900 °C)

1

+/-1,5 °C (-40...375 °C)
+/-0,004|t| (375...800 °C)

K
(NiCr-Ni)

2

+/-2,5 °C (-40...333 °C)
+/-0,0075|t| (333...1200 °C)

1

+/-1,5 °C (-40...375 °C)
+/-0,004|t| (375...1000 °C)

N
(NiCrSi-NiSi)

2

+/-2,5 °C (-40...333 °C)
+/-0,0075|t| (333...1200 °C)

1

+/-1,5 °C (-40...375 °C)
+/-0,004|t| (375...1000 °C)

Thermocouples made from precious metals

S
(PtRh10%-Pt)

2

+/-1.5 °C (0...600 °C)
+/-0,0025|t| (600...1600 °C)

1

+/-1 °C (0...1100 °C)
+/-[1+0,003(t-1100)] (1100...1600 °C)

R
(PtRh13%-Pt)

2

+/-1.5 °C (0...600 °C)
+/-0,0025|t| (600...1600 °C)

1

+/-1 °C (0...1100 °C)
+/-[1+0,003(t-1100)] (1100...1600 °C)

B
(PtRh30%-PtRh6%)

3

+/-4 °C (600...800 °C)
+/-0,005|t| (800...1700 °C)

2

+/-0,0025|t| (600...1700 °C)

 

 

Thermocable, compensation cable

  

Thermo- and compensation cables are used in order to bridge the distance between the sensor (ceramic leg) and the electronics (transmitter) in the most economical manner.

Thermocables are manufactured from the same material as the respective thermocouple.

Compensation cables however are manufactured from special material that, in a limited temperature range, have the same thermoelectric properties as the respective thermocouple.

 

  
   

TC connection

 

 

 

  

There is an extension cable or a compensating cable for each type of thermocouple which reacts in a similar manner as the respective thermocouple (compatible) within a temperature range up to maximal 200 °C. Also the extension cables and a compensating cables are more economical and easier to install than the insulated thermocouple wires.

The following table shows the mostly used insulation materials and their maximum temperature resistance for thermo- and compensation cables:

  • Material t max
  • PVC 80 °C
  • Silicon 180 °C
  • PTFE 260 °C
  • Glass fibre 400 °C