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

Marking Type of thermocouple Temperature range for
long-term application
[°C]
Temperature range for
short-term application
[°C]
T: Cu-CuNi copper-copper/nickel or copper/constantan -100 … +400 -200 … +600
E: NiCr-CuNi nickel/chrome-copper/nickel or nickel/chrome-constantan -100 … +700 -200 … +1000
J: Fe-CuNi iron-copper/nickel or iron-constantan -100 … +700 -200 … +900
K: NiCr-NiAl nickel/chrome-nickel aluminum -100 … +1000 -200 … +1300
N: NiCrSi-NiSi nickel/chrome/silicon-nickel/silicon -100 … +1000 -200 … +1300
S: PtRh10-Pt platinum/rhodium 10%-platinum 0 … +1300 0 … +1600
R: PtRh13-Pt platinum/rhodium 13%-platinum 0 … +1300 0 … +1600
B: PtRh30-PtRh6 platinum/rhodium 30%-platinum/rhodium 6% 0 … +1300 0 … +1800

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

Thermo-electric potential [mV]
T °C T J K N S R B
-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 -0.757 0.995 -0.778 -0.518 -0.103 -0.100
0 0 0 0 0 0 0 0
20 0.790 1.019 0.798 0.525 0.113 0.111 -0.003
40 1.612 2.059 1.612 1.065 0.235 0.232 0
60 2.468 3.116 2.436 1.619 0.365 0.363 0.006
80 3.358 4.187 3.267 2.189 0.502 0.501 0.017
100 4.279 5.269 4.096 2.774 0.646 0.647 0.033
120 5.228 6.360 4.920 3.374 0.795 0.800 0.053
140 6.206 7.459 5.735 3.989 0.950 0.959 0.078
160 7.209 8.562 6.540 4.618 1.110 1.124 0.107
180 8.237 9.669 7.340 5.259 1.273 1.294 0.141
200 9.288 10.779 8.138 5.913 1.441 1.469 0.178
220 10.362 11.889 8.940 6.579 1.612 1.648 0.220
240 11.458 13.000 9.747 7.255 1.786 1.831 0.267
260 12.574 14.110 10.561 7.941 1.962 2.017 0.317
280 13.709 15.219 11.382 8.637 2.141 2.207 0.372
300 14.862 16.327 12.209 9.341 2.323 2.401 0.431
320 16.032 17.434 13.040 10.054 2.507 2.597 0.494
340 17.219 18.538 13.874 10.774 2.692 2.796 0.561
360 18.422 19.642 14.713 11.501 2.880 2.997 0.632
380 19.641 20.745 15.596 12.234 3.069 3.201 0.707
400 20.872 21.848 16.439 12.974 3.259 3.408 0.787
420 22.952 17.243 13.719 3.451 3.616 0.870
440 24.057 18.091 14.469 3.645 3.827 0.957
460 25.164 18.941 15.255 3.840 4.040 1.048
480 26.276 19.792 15.984 4.036 4.255 1.143
500 27.393 20.644 16.748 4.233 4.471 1.242
520 28.516 21.497 17.515 4.432 4.690 1.344
540 29.647 22.350 18.286 4.632 4.910 1.451
560 30.788 23.203 19.059 4.833 5.133 1.561
580 31.939 24.055 19.835 5.035 5.357 1.675
600 33.102 24.905 20.613 5.239 5.583 1.792
620 34.279 25.755 21.393 5.443 5.812 1.913
640 35.470 26.602 22.175 5.649 6.041 2.037
660 36.675 27.447 22.958 5.857 6.273 2.165
680 37.896 28.289 23.742 6.065 6.507 2.296
700 39.132 29.129 24.527 6.275 6.743 2.431
720 40.382 29.965 25.312 6.486 6.980 2.569
740 41.645 30.798 26.098 6.699 7.220 2.710
760 42.919 31.628 26.883 6.913 7.461 2.854
780 44.203 32.453 27.669 7.128 7.705 3.002
800 45.494 33.275 28.455 7.486 7.950 3.154
820 46.786 34.093 29.239 7.563 8.197 3.308
840 48.074 34.908 30.024 7.783 8.446 3.466
860 49.353 35.718 30.807 8.003 8.697 3.626
880 50.622 36.524 31.590 8.226 8.950 3.790
900 51.877 37.326 32.371 8.449 9.205 3.957
920 53.119 38.124 33.151 8.674 9.461 4.127
940 54.347 38.918 33.930 8.900 9.720 4.299
960 55.561 39.708 34.707 9.128 9.980 4.475
980 56.763 40.494 35.482 9.357 10.242 4.653
1000 57.953 41.276 36.256 9.587 10.506 4.834
1020 59.134 42.053 37.027 9.819 10.771 5.018
1040 60.307 42.826 37.795 10.051 11.039 5.205
1060 61.473 43.595 38.562 10.285 11.307 5.394
1080 62.634 44.397 39.326 10.520 11.578 5.585
1100 63.792 45.119 40.087 10.757 11.850 5.780
1120 64.948 45.873 40.845 10.994 12.123 5.976
1140 66.102 46.623 41.600 11.232 12.397 6.175
1160 67.255 47.367 42.352 11.471 12.673 6.377
1180 68.406 48.105 43.101 11.710 12.950 6.580
1200 69.553 48.838 43.846 11.951 13.228 6.786
1220 49.565 44.588 12.191 13.507 6.995
1240 50.286 45.326 12.433 13.786 7.205
1260 51.000 46.060 12.554 14.066 7.417
1280 51.708 46.789 12.917 14.347 7.632
1300 52.410 47.513 13.159 14.629 7.848
1320 53.106 13.402 14.911 8.066
1340 53.795 13.644 15.193 8.286
1360 54.479 13.887 15.475 8.508
1380 14.130 15.758 8.731
1400 14.373 16.040 8.956
1420 14.615 16.323 9.182
1440 14.857 16.605 9.410
1460 14.978 16.887 9.639
1480 15.341 17.169 9.868
1500 15.582 17.451 10.099
1520 15.822 17.732 10.331
1540 16.062 18.012 10.563
1560 16.301 18.292 10.796
1580 16.539 18.571 11.029
1600 16.777 18.849 11.263
1620 17.013 19.126 11.497
1640 17.249 19.402 11.731
1660 17.483 19.667 11.965
1680 17.717 19.951 12.199
1700 17.947 20.222 12.433

Tolerances for thermocouples (EN 60584-2)

Permissible deviations of thermocouples
type K,N type J type S, R type T type B
Temperature [°C] ∆t Temperature [°C] ∆t Temperature [°C] ∆t Temperature [°C] ∆t Temperature [°C] ∆t
-40÷375 1.5ºC -40÷375 1.5ºC 0÷1100 1ºC -40÷125 0.5 ºC
375÷1000 0.4% 375 ÷750 0.4% 1100÷1600 (*) 125÷350 0.4%
-40 ÷333 2.5ºC -40÷333 2.5ºC 0÷600 1,5ºC -44÷133 1.0ºC
333÷1200 0.75% 333÷750 0.75% 600 ÷1600 0.25% 133÷350 0.75% 600÷1700 0.25%

(*) 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.

Marking Properties
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)
0.25 5 ms 2 ms
0.5 14 ms 8 ms
1.0 0.18 s 0.14 s
1.5 0.2 s 0.15 s
3.0 0.5 s 0.4 s
4.5 1.2 s 0.7 s
6.0 2.4 s 1.2 s
8.0 3.9 s 2.1 s

Thermocouple measuring junctions

1a Single 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
1b Single measuring junction, galvanically isolated from sensor sleeve. Longer time constant. Applied in conducting
environments or where electric isolation from the measurement system is required.
2a Twin 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)
2ab Twin measuring junction., isolated from sheath and connected together. Longer time constant. Applied in
conducting environments and when isolation from the measurement system is required.
2b Twin 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.
1c Single 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
2c Twin 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.