Thermoelectric sensors react to temperature changes by changing the thermoelectric force of the thermocouple built into them.
Thermocouple – two conductors made of different materials, connected to each other at one end and forming part of a system that uses a thermoelectric effect to measure temperature (the Seebeck effect).
The thermoelectric effect consists in creating a thermoelectric force due to the temperature difference between two welds: the measuring (combined ends of the thermocouple), which it acts in the measured temperature and reference (free ends of thermocouples), which is at a known temperature (usually 0°C).

Thermocouple types

MarkingType of thermocoupleTemperature range for
long-term application
[°C]
Temperature range for
short-term application
[°C]
T: Cu-CuNicopper-copper/nickel or copper/constantan-100 … +400-200 … +600
E: NiCr-CuNinickel/chrome-copper/nickel or nickel/chrome-constantan-100 … +700-200 … +1000
J: Fe-CuNiiron-copper/nickel or iron-constantan-100 … +700-200 … +900
K: NiCr-NiAlnickel/chrome-nickel aluminum-100 … +1000-200 … +1300
N: NiCrSi-NiSinickel/chrome/silicon-nickel/silicon-100 … +1000-200 … +1300
S: PtRh10-Ptplatinum/rhodium 10%-platinum0 … +13000 … +1600
R: PtRh13-Ptplatinum/rhodium 13%-platinum0 … +13000 … +1600
B: PtRh30-PtRh6platinum/rhodium 30%-platinum/rhodium 6%0 … +13000 … +1800

Thermo-electric characteristics of thermocouples (short-form data) /EN 60584-1/

Thermo-electric potential [mV]
T °CTJKNSRB
-100-3.379-4.633-3.554-2.407
-80-2.788-3.786-2.920-1.972
-60-2.153-2.893-2.243-1.509
-40-1.475-1.961-1.527-1.023-0.194-0.188
-20-0.7570.995-0.778-0.518-0.103-0.100
00000000
200.7901.0190.7980.5250.1130.111-0.003
401.6122.0591.6121.0650.2350.2320
602.4683.1162.4361.6190.3650.3630.006
803.3584.1873.2672.1890.5020.5010.017
1004.2795.2694.0962.7740.6460.6470.033
1205.2286.3604.9203.3740.7950.8000.053
1406.2067.4595.7353.9890.9500.9590.078
1607.2098.5626.5404.6181.1101.1240.107
1808.2379.6697.3405.2591.2731.2940.141
2009.28810.7798.1385.9131.4411.4690.178
22010.36211.8898.9406.5791.6121.6480.220
24011.45813.0009.7477.2551.7861.8310.267
26012.57414.11010.5617.9411.9622.0170.317
28013.70915.21911.3828.6372.1412.2070.372
30014.86216.32712.2099.3412.3232.4010.431
32016.03217.43413.04010.0542.5072.5970.494
34017.21918.53813.87410.7742.6922.7960.561
36018.42219.64214.71311.5012.8802.9970.632
38019.64120.74515.59612.2343.0693.2010.707
40020.87221.84816.43912.9743.2593.4080.787
42022.95217.24313.7193.4513.6160.870
44024.05718.09114.4693.6453.8270.957
46025.16418.94115.2553.8404.0401.048
48026.27619.79215.9844.0364.2551.143
50027.39320.64416.7484.2334.4711.242
52028.51621.49717.5154.4324.6901.344
54029.64722.35018.2864.6324.9101.451
56030.78823.20319.0594.8335.1331.561
58031.93924.05519.8355.0355.3571.675
60033.10224.90520.6135.2395.5831.792
62034.27925.75521.3935.4435.8121.913
64035.47026.60222.1755.6496.0412.037
66036.67527.44722.9585.8576.2732.165
68037.89628.28923.7426.0656.5072.296
70039.13229.12924.5276.2756.7432.431
72040.38229.96525.3126.4866.9802.569
74041.64530.79826.0986.6997.2202.710
76042.91931.62826.8836.9137.4612.854
78044.20332.45327.6697.1287.7053.002
80045.49433.27528.4557.4867.9503.154
82046.78634.09329.2397.5638.1973.308
84048.07434.90830.0247.7838.4463.466
86049.35335.71830.8078.0038.6973.626
88050.62236.52431.5908.2268.9503.790
90051.87737.32632.3718.4499.2053.957
92053.11938.12433.1518.6749.4614.127
94054.34738.91833.9308.9009.7204.299
96055.56139.70834.7079.1289.9804.475
98056.76340.49435.4829.35710.2424.653
100057.95341.27636.2569.58710.5064.834
102059.13442.05337.0279.81910.7715.018
104060.30742.82637.79510.05111.0395.205
106061.47343.59538.56210.28511.3075.394
108062.63444.39739.32610.52011.5785.585
110063.79245.11940.08710.75711.8505.780
112064.94845.87340.84510.99412.1235.976
114066.10246.62341.60011.23212.3976.175
116067.25547.36742.35211.47112.6736.377
118068.40648.10543.10111.71012.9506.580
120069.55348.83843.84611.95113.2286.786
122049.56544.58812.19113.5076.995
124050.28645.32612.43313.7867.205
126051.00046.06012.55414.0667.417
128051.70846.78912.91714.3477.632
130052.41047.51313.15914.6297.848
132053.10613.40214.9118.066
134053.79513.64415.1938.286
136054.47913.88715.4758.508
138014.13015.7588.731
140014.37316.0408.956
142014.61516.3239.182
144014.85716.6059.410
146014.97816.8879.639
148015.34117.1699.868
150015.58217.45110.099
152015.82217.73210.331
154016.06218.01210.563
156016.30118.29210.796
158016.53918.57111.029
160016.77718.84911.263
162017.01319.12611.497
164017.24919.40211.731
166017.48319.66711.965
168017.71719.95112.199
170017.94720.22212.433

Tolerances for thermocouples (EN 60584-2)

Permissible deviations of thermocouples
type K,Ntype Jtype S, Rtype Ttype B
Temperature [°C]∆tTemperature [°C]∆tTemperature [°C]∆tTemperature [°C]∆tTemperature [°C]∆t
-40÷3751.5ºC-40÷3751.5ºC0÷11001ºC-40÷1250.5 ºC
375÷10000.4%375 ÷7500.4%1100÷1600(*)125÷3500.4%
-40 ÷3332.5ºC-40÷3332.5ºC0÷6001,5ºC-44÷1331.0ºC
333÷12000.75%333÷7500.75%600 ÷16000.25%133÷3500.75%600÷17000.25%

(*) For thermocouples type S and R permissible deviation is calculated according to the formula:: $[1+(t-1100)·0,003]°C$

Sheted thermocouples

Sheathed thermocouples are shielded by a nickel-chromium steel tube within which are housed the thermo-electric wires and isolation
material in the form of heavily compressed manganese oxide (MgO).
The material of the sheath provides the mechanical and chemical shield for the fused measurement end and high resistance to many
aggressive environments.
At one end the thermocouple is welded creating the fused end for measurement. The external shield is hermetically sealed by welding.
The other end of the thermocouple is connected to a compensating cable, plug- socket connector or connector block in the sensor head.
Due to the heavily compressed isolating layer and the metallurgical structure of the thermo-electrode and sleeve, the thermo-elements
are bendable and can be bent to a minimum radius of five times their external diameter.
The main advantage of sheathed thermocouples are: small external diameters, long service life and flexibility permitting them to be bent
and screwed in place, high resistance to shock and vibration and low thermal inertia.

MarkingProperties
INCONEL 600
(75%Ni, 16%Cr, 8%Fe)
good general resistance to corrosion
very good resistance to oxidation
not recommended for atmospheres containing CO2 and sulfur >550°C
not recommended for atmospheres containing sodium > 750°C
maximum operating temperature in air 1150°C
NICROBELL
(73%Ni, 22%Cr, 3%Mo, 1,4%Si)
excellent resistance to oxidation
maximum operating temperature in air 1250°C
remaining parameters as for Inconel
PtRh10
(90%Pt, 10%Rh)
very good resistance to collagens, acetic acids, solutions of Na-HCl
high resistance to oxidation to 1300°C
resistant to 1200°C in atmospheres containing sulfur and silicon
not recommended for atmospheres containing phosphor
maximum working temperature to 1600°C
TANTALUM (Ta)very prone to oxidation above 300°C
very resistant to corrosion
resistant to most acids and alkalis
reacts to cold solutions of fluoride and hydrofluoric acid
reacts with chlorine at high temperatures
very high thermal resistance in vacuum, in neutral and reducing atmospheres
maximum working temperature to 2200°C
TUNGSTEN (W)low chemical reactivity
high mechanical strength and hardness
resistance to sulfuric and hydrochloric acids
at high temperatures reacts with oxygen, hydrogen, nitrogen,carbon and water vapor
maximum operating temperature 3300°C

Dynamic properties of sheathed thermocouples

Time constants for sheathed thermocouples of different diameters. (Time to reach 63% of actual thermocouple temperature after step change of the temperature of gas or liquid)
sheath diameter [mm]isolated measuring junction (type b)grounded measuring junction (type a)
0.255 ms2 ms
0.514 ms8 ms
1.00.18 s0.14 s
1.50.2 s0.15 s
3.00.5 s0.4 s
4.51.2 s0.7 s
6.02.4 s1.2 s
8.03.9 s2.1 s

Thermocouple measuring junctions

1aSingle measuring junction (single thermocouple), with galvanic ground connection with sheath. Short time
constant. Measuring junction isolated from chemical and mechanical environmental influences. Applied in non-
conducting environments
1bSingle measuring junction, galvanically isolated from sensor sleeve. Longer time constant. Applied in conducting
environments or where electric isolation from the measurement system is required.
2aTwin measuring junction (twin thermocouple), with galvanic ground connection with sheath. Short time constant.
Measuring junction isolated from chemical and mechanical environmental influences. Applied in non-conducting
environments. May be applied in demanding situations allowing continuous measurement of process temperature
(damage to one measuring circuit does not cause failure)
2abTwin measuring junction., isolated from sheath and connected together. Longer time constant. Applied in
conducting environments and when isolation from the measurement system is required.
2bTwin measuring junction, isolated from sheath and from each other. Longer time constant. Applied in electrically
conducting environments and when isolation from the measurement system is required.
1cSingle measuring junction, not protected or protruding outside the sheath, exposed.
Shortest time constant.
Measuring junction sensitive to mechanical damage and not resistant to atmospheric corrosion
2cTwin measuring junction , not protected or protruding outside the sheath, exposed. Shortest time constant.
Measuring junction sensitive to mechanical damage and not resistant to atmospheric corrosion. May be applied
in demanding situations allowing continuous measurement of process temperature (damage to one measuring
circuit does not cause failure).

Compensating cables (EN 60584-3)

Compensating cables are made of the same materials as thermocouple or an alloy substitute that is not identical to the thermocouple,
but have the same properties as a thermocouple.
Alternative materials are used for K and N-type thermocouples and for thermocouples of precious metals type R and S (for B-type
thermocouples are applied copper wires in the temperature range up to + 100 ° C).
Compensating cables can be used in the temperature range up to 200 ° C.
Wires for compensating cables are standardized in EN 60584-3.
The thermoelectric voltages within acceptable operating temperatures correspond to the thermoelectric voltage for thermocouples
according to standard EN 60584-1. Deviation limits for compensation wires are given in standard EN 60584-3.
Compensating cables are manufactured in two classes.
Class 1 – compensation cables made from the same materials as the thermocouple.
Class 2 – compensation cables made of the same materials as the thermocouple or substitute materials.
Colour coding of compensating cables is in accordance with EN 60584-3.
We supply cables to class 1.

Thermoelectric temperature sensors made of thermocouple wires

These temperature sensors comprise a thermocouple conductor in a protection sheath. The maximum operating temperature of such a
sensor is dependent on the type of isolation of the conductor. Thermocouple sensors are made with the following isolating materials

Materiał
izolacji
Temperatura
maksymalna
przewodu
PCV+80°C
silikon+180°C
PTFE (teflon)+260°C
włókno szklane+400°C

The external cable isolation may be enclosed by a stainless steel braid or a stainless steel armored hose.
As sensor core we apply thermocouple solid wires (diameter 0.5mm) or thermocouple stranded wires 0.22mm2 , 0.35mm2 or 0.50mm2 .

Thermoelectric temperature sensors with connection head

These temperature sensors comprises of a protection tube, measurement insert and a connection head with an internal terminal block.
The insert may be a replaceable element of the sensor or not. Sensors are available with heads in several arrangements, which differ
according to form, material of construction and dimensions.

Przyłączenia głowicowych czujników termoelektrycznych

Dynamic properties of temperature sensors

Time constant  (t) is the time, after a step change in temperature, which the sensor needs to reach a defined reading
Time constant (t05), is the time required to reach 50% of the step change in temperature.
Time constant (t09), is the time required to reach 90% of the step change in temperature

Time constants are given for air or water under flow conditions.