Standard colours for thermocouples compensating cables
Termotech markets a series of cables for signal transmission and for thermocouples; the type of insulation and the production of the cables depends on the temperature and type of atmosphere in which the cable will be placed.
Some of the physical characteristics of the different types of insulation cables are given below:
| Insulator | Temperature range | Abrasion resistance | Humidity resistance | Flame behavior | Notes |
|---|---|---|---|---|---|
| A = Excellent, B = Good, C = Sufficient, D = Poor | |||||
| Fiber glass | +400 °C | D | D | Not combustible | Good high temperature resistance |
| Silicone rubber | -40 +200 °C | C | B | Self-extinguishing | Excellent flexibility even at low temperatures |
| Fluoropolymer Mfa | -200 +250 °C | A | A | Self-extinguishing | Very good resistance to chemical agents and excellent mechanical characteristics |
| P.V.C | -20 +105 °C | B | B | Self-extinguishing | Good mechanical and electric characteristics |
| KAPTON® | -200 +400 °C | B | B | Self-extinguishing | Excellent dielectrical and chemical characteristics |
In measuring temperature with thermocouples is vital that the voltage signal produced by them is transmitted unaltered to the measuring device; for this reason the cable used for this connection must have thermoelectrical characteristics which are the same as, or similar to, those of the thermocouple.
There are three types of cable for thermocouples:
Thermocouple cables are used to construct true and proper thermocouple sensors which guarantee all the thermoelectrical characteristics of the thermocouple for the entire temperature range defined by the reference standard adopted.
Extension cables are generally used to connect the thermocouple to the measuring device; the conductors of this are of the same type as those of the thermocouples but guarantee their thermoelectrical properties within a limited temperature range (generally 0 - 200°C).
Compensation cables are also used to connect the thermocouples to the measuring devices but, although they maintain unaltered all their thermoelectrical properties for a limited temperature range (0-100 °C or 0-150 °C), they comprise conductors of a different type from those of the thermocouples.
For example the compensated cable for "S" type thermocouples has a copper positive conductor and a copper-nickel alloy negative conductor.
The following table shows the composition of the conductors and the tolerances for extension and compensation cables with reference to the most common international standards.
| Standard | Type | Conductors | Range °C | Error limit | TC's temperature | |
|---|---|---|---|---|---|---|
| 1 | 2 | |||||
| DIN 43710 | UX | Cu/CuNi | 0 +200 | - | ±3,0 °C | - |
| LX | Fe/CuNi | 0 +200 | - | ±3,0 °C | - | |
| IEC 584 | TX | Cu/CuNi | -25 +100 | ±30 µV (±0,5 °C) | ±60 µV (±1,0 °C) | 300 °C |
| EX | NiCr/CuNi | -25 +200 | ±120 µV (±1,5 °C) | ±200 µV (±1,5 °C) | 500 °C | |
| JX | Fe/CuNi | -25 +200 | ±85 µV (±1,5 °C) | ±85 µV (±1,5 °C) | 500 °C | |
| KX | NiCr/NiAl | -25 +200 | ±60 µV (±1,5 °C) | ±100 µV (±1,5 °C) | 900 °C | |
| KCA | Fe/CuNi | 0 +150 | - | ±100 µV (±2,5 °C) | 900 °C | |
| KCB | Cu/CuNi | 0 +100 | - | ±100 µV (±2,5 °C) | 900 °C | |
| RCA | Cu/CuNi | 0 +100 | - | ±30 µV (±2,5 °C) | 1000 °C | |
| RCB | Cu/CuNi | 0 +200 | - | ±60 µV (±5,0 °C) | 1000 °C | |
| SCA | Cu/CuNi | 0 +100 | - | ±30 µV (±2,5 °C) | 1000 °C | |
| SCB | Cu/CuNi | 0 +200 | - | ±60 µV (±5,0 °C) | 1000 °C | |
| NX | Nicrosil/Nisil | -25 +200 | ±60 µV (±1,5 °C) | ±100 µV (±1,5 °C) | 900 °C | |
| BC | Alloy Cu/Cu | 0 +100 | - | ±40 µV (±3,5 °C) | 1400 °C | |
| ANSI MC96.1-1982 | TX | Cu/CuNi | 0 +100 | ±0,50 °C | ±1,10 °C | |
| EX | NiCr/CuNi | 0 +200 | - | ±1,70 °C | ||
| JX | Fe/CuNi | 0 +200 | ±1,10 °C | ±2,20 °C | ||
| KX | NiCr/NiAl | 0 +200 | - | ±2,20 °C | ||
| SX | Cu/CuNi | 0 +200 | - | ±57 µV (±5,0 °C) | > 870 °C | |
| NX | Nicrosil/Nisil | |||||
| BX | Cu/Cu | 0 +100 | - | +0,000 µV ("0 °C) -33 µV (±3,7 °C) | > 1000 °C | |
| BX | Alloy Cu/Cu | 0 +200 | - | -33 µV (±3,7 °C) | > 1000 °C | |
