Application of extension and compensating cables
Construction of a thermocouple with connection cable or compensating cable
Temperature is an important factor in many areas concerning the environment, scientific research and production. It is a thermodynamic variable that defines the heat content of a material. Material strength changes with alternating temperature. As a consequence, the characteristics of materials have to be examined at different temperatures. To obtain a temperature value, defined temperature parameters are used. Here the parameters can be defined, for example, as the freezing and boiling points of water. For temperature measurement temperature dependent characteristics of materials have to be taken into account. These include such things as thermal expansion (expansion thermometer), the dependance of the electric resistance on metallic conductors (electrical thermometer) and electromotive force (thermocouple) etc. A temperature measuring device with a thermocouple as a data indicator tends to consist of the thermometer itself with a measuring point, an extension cable, a cold junction with a specified constant temperature and a voltmeter. The value of the electromotive force (EMF) produced by the thermocouple is determined by the difference between the measuring temperature and the so-called free ends of the thermocouple which are mounted in the connection head. As the connection head is usually relatively close to the measuring point, it is frequently exposed to temperature fluctuations. For this reason, a connection cable with the same thermo-electric properties as the thermocouple is used between the thermocouple and the cold junction. This link-up provides the compensating/extension cable.
Materials
We differentiate between thermocouple cable and compensating cable. Cables made of original materials are called extension or thermocouple cables, whereas conductor materials made of substitutes are known as compensating cables.
Compensating cables
The compensating wires and strands are composed of alloys which do not have to be identical with the corresponding thermocouple. Substitute material means that the thermo-electric characteristics in the allowed temperature range (usually 0 up to +200 °C) for the compensating cable must be the same as those of the corresponding thermocouple. They are identified with the letter ”C“ adapted to DIN IEC 584. The ”C” appears behind the code letter identifying the thermocouple, for example ”KC”.
Thermocouple Extension Cables
Extension cables are made of conductors with identical nominal structure to the corresponding thermocouple. They are identified with the letter ”X” adapted to DIN IEC 584, which appears behind the code letter identifying the thermocouple, for example ”JX”. They are normally tested within a temperature range of 0 up to +200°C.
Thermocouple Cables
Thermocouple cables consist of the same element material as the thermocouple and are tested for the same temperatures. These SAB special cables are manufactured on customer request. PVC, fibre-glass and SABtex insulated or sheathed compensating and extension cables are not suitable for outdoor use. Exception: PVC sheathed solid conductors can be used for underground laying.
Thermocouple - electrical characteristics
Material | Specific electric resistance at 20°C µ Ω x cm | Resistance in Ω/m mm ø mm ø 0,20 1,38 | |
|---|---|---|---|
| Cu Ni | 49,0 | 15,60 | 0,328 |
| So Ni | 51,0 | 16,26 | 0,341 |
| Ni Cr | 72,0 | 22,90 | 0,481 |
| Ni | 27,0 | 8,59 | 0,180 |
| So Pt | 12,0 | 3,82 | 0,0802 |
| E-Cu | 1,7 | 0,54 | 0,011 |
| Fe | 12,0 | 3,82 | 0,08 |
| BPX | 12,5 | 3,98 | 0,084 |
| Ni Cr Si | 98,0 | 31,20 | 0,655 |
| Ni Si | 34,0 | 10,80 | 0,227 |
| So Ni Si | 52,0 | 16,55 | 0,347 |
Because the thermal electromotive force values are decisive, the indicated specific resistance and meter resistance figures can only be considered as approximate values, tolerances have to be agreed between producer and customer. Limit deviations within the thermoelectric voltage range can only be guaranteed for positive and negative conductors bought together from S BRÖCKSKES GmbH & Co. KG.
SAB thermocouple code acc. to IEC 60584
| for thermocouple | EMK at 100 °C' in mV | cable type | SAB thermocouple code strands single wire | |
|---|---|---|---|---|
| Type T | 4,28 | TX | …58 | …88 |
| Type J | 5,27 | JX | …52 | …82 |
| Type K | 4,10 | KCA | …95 | …15 |
| Type K | 4,10 | KCB | …99 | …19 |
| Type K | 4,10 | KX | …54 | …84 |
| Type E | 6,32 | EX | …53 | …83 |
| Type R/S | 0,65 | R/SCB | …97 | …17 |
| Type N | 2,77 | NC | …91 | …11 |
SAB thermocouple code acc. to DIN 43710 / 43714
We continue to manufacture compensating and extension cables with colour code acc. to DIN 43714
| for thermocouple | EMK at 100 °C' in mV | cable type | SAB thermocouple code strands single wire | |
|---|---|---|---|---|
| Type L | 5,37 | LX | …92 | …12 |
| Type K | 4,10 | KCA | …94 | …14 |
| Type R/S | 0,65 | R/SCB | …96 | …16 |
| Type U | 4,25 | UX | …98 | …18 |
| Type B | 0,00 | BC-100 | …01 | …21 |
| Type B | 0,033 | BC-200 | …02 | …22 |
Example:
Type A 12 D for thermocouple type J acc. to DIN IEC 584 = item no. 044512 82
Type A 9-4 LSY for thermocouple type L acc. to DIN 43713 = item no. 046204 92
Customized Compensating Cables & Thermocouple Extention Cables
In addition to our standard compensating cables featured on the following pages, we also produce special cables on customer request and according to almost all known international standards. For special compensating cables we would request the following information:
- stranded or solid conductor
- no. of cores
- cross-section
- element-type
- core insulation and sheath material
- screening or armour requirements
- temperature range
We manufacture customized compensating and thermocouple extension cables from a minimum quantity of 500 m or 1000 m. Please contact us directly.
Pleace notice
In addition to our standard compensating cables, which are described below, we also manufacture compensating cables according to your design requirements and to almost all known foreign standards. We require the following information for special equalising cables: Stranded or solid conductor, number of cores, cross-section, element type, core and sheath material, shielding or armouring and the temperature application range. The minimum quantity for these special versions is 500 m or 1000 m.