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COMPENSATING & EXTENSION WIRE CABLES |
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These cables form part of the every industry and are used as accessories to temparature measuring instruments. Thermocouple used for industrial application are normally not connected to the measuring instrument, generally the thermocouple wires are round from the measuring point to the terminal of electrical thermometer. The extension wire is not used in temparature range above 200° C it has to show the thermoelectric voltage of the thermocouple only upto 200° C. |
The extension leads, for noble metal thermocouple as PtRh-Ptstr made of special cheaper material. Through the composition of these special materials does not corresponds to that of the thermocouple itself yet the thermoelectric voltage is same in a temparature range upto 200° C. Such extension leads are called compensating extension wire. |
According to ANSI, letter 'X' follow the code letter of thermocouple to represent the extension / compensating wire of respective thermocouple. The type designation of thermocouple and materials of extension / compensating wire are as under : |
Thermocouple type as per ANSI MC 96-1 |
Temp. EMF at 100° C corresponding to 0° C ref. junction ( mv ) |
Nom. temparature range (° C ) |
Thermocouple material |
Material of Extension / Compensating wire |
as per ANSI MC 96-1 |
as per IS-8784/87 |
B |
0.033 |
0 to 1820 |
+ve Platinum Rhodium
-ve -do- |
*+ve Copper
*-ve Copper |
*i) +ve Cu
-ve Cu |
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*ii)+ve Cu
-ve Cu
Nickel alloy |
E |
6.317 |
-270 to 1000 |
+ve Nickel Chromium
-ve Copper Nickel |
+ve Nickel Chromium
-ve Copper Nickel |
+ve Nickel Chromium
-ve Constantan. |
J |
5.268 |
-210 to 760 |
+ve Iron
-ve Copper Nickel |
+ve Iron
-ve Copper Nickel |
+ve Iron
-ve Constantan. |
K |
4.095 |
-270 to 1372 |
+ve Nickel Chromium
-ve Nickel Aluminium |
+ve Nickel Chromium
-ve Nickel Aluminium |
i) +ve Nickel Chromium
-ve Nickel Aluminium |
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*ii) +ve Iron
-ve Copper Nickel Alloy |
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*iii) +ve Copper
-ve Copper Nickel Alloy |
R & S |
0.647 & 0.645 |
-50 to 1768 |
+ve Platinum Rhodium
-ve Platinum |
*+ve Copper
-ve Copper Nickel Alloy |
*+ve Copper
-ve Copper Nickel Alloy |
T |
4.277 |
-270 to 400 |
+ve Copper
-ve Copper Nickel |
+ve Copper
-ve Copper Nickel |
+ve Copper
-ve Constantan |
| * Compensating Wires |
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Extension / Compensating wire cables are manufactured in different construction as per customer's requirement using thermoplastic / elastomeric or fluroplastic material as dielectric. However the most common construction normally sought by customer is as under : |
1) Conductor - Pair of wires depending upon the type thermocouple for which it is to be used. |
2) Insulation - PVC. |
3) Pairing - +Ve and -Ve wires twisted together to form pair. |
4) Individual Pair shield - Aluminium backed mylar tape with min 25% overlap and in contact with drain wire. |
5) Bundling - Pairs laid up together and lapped with polyster tape. |
6) Collective shield - Aluminium backed mylar tape with min 25% overlap and in contact with drain wire. |
7) Inner Sheath - PVC |
8) Armouring - Galvanized round steel wire / flat strip armouring. |
9) Outer sheath - PVC outer sheath may have additional FR ( flame retardant ) / FRLS ( flame retardant low smoke ) properties. |
10) Ref. STD. Gen. to IS - 1554/1/88 and IS - 8784/87 |
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