CABLES

 

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
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

A = Excellent, B = Good, C = Sufficient, D = Poor

 

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 cable
- Extension cable
- Compensation cable

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

 

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