Basic information about temperature sensors

Temperature (outdoor, indoor, of technical devices, etc.) can be measured by a wide range of CFox and RFox modules, or by separate temperature sensors connected to the analogue inputs of CFox, RFox and Foxtrot modules. Tab. 7 gives a brief overview of the most widely used temperature measurements and the recommended sensors; Tab. 8 shows the ranges of analogue inputs of individual CFox and RFox modules.

 

Basic types of temperature sensors (a brief overview)

The Pt1000 – a platinum resistance temperature sensor with the R₀ = 1,000 Ω basic resistance at 0 °C. There are also produced sensors with a different resistance at 0 °C: the Pt100 (R₀ = 100 Ω), Pt500 and others.

The quality of the platinum sensor is high, is features long-term temperature stability, a disadvantage is somewhat lower sensitivity (lower Tk) and a higher price.

Tk = 3,850 is the standard temperature coefficient of resistance in platinum sensors.

There is also used the so-called "American version" with Tk = 3910.

The parameters are defined by the EN 60751 standard: Industrial platinum resistance thermometers and platinum temperature sensors.

 

Tab. 1. Tolerance classes for platinum resistance thermometers and platinum temperature sensors

The tolerance class	B	A
Basic tolerance range	± 0.3 + 0.005. l t l °C	± 0.15 + 0.002. l t l °C
The temperature range	-200 ÷ +850 °C	-200 ÷ +650 °C

The most common class for standard applications is class B.

 

The temperature coefficient of resistance defines the relation between the resistance and the temperature. It is defined in several ways, e.g. the coefficient of Pt1000 sensors, the European implementation:

The temperature coefficient of resistance α = 3.85 x 10^–3[ °C^-1]

or Tk = 3,850 ppm/ °C (correctly 3851, after a refinement of the value in the A2 appendix of the ČSN EN 60751 standard),

or W₁₀₀ = 1.385 (the ratio of resistance R₁₀₀ at 100 °C and resistance R₀ at 0 °C).

 

Ni1000 - a nickel resistance temperature sensor with the basic resistance at 0 °C R₀=1000 Ω. A standard resistance sensor, in comparison with Pt sensors it has a smaller temperature measuring range, good stability, is very popular in measurement and control applications.

By default, nickel sensors are supplied with the temperature coefficient of resistance at Tk = 6,180 (W₁₀₀ = 1.618) or Tk = 5,000 ( W₁₀₀ = 1.500).

 

Tab. 2. Tolerance classes for nickel resistance thermometers

The tolerance class	B
Basic tolerance range	± 0.4 + 0.007. l t l °C
The temperature range	-50 ÷ +250 °C

 

NTC 12k - thermistors with a negative temperature coefficient of resistance. Inexpensive sensors, with a smaller temperature range and worse precision. They have a very nonlinear characteristic.

NTC 12k – a sensor with a 12k resistance at 25 °C. There are produced a number of NTC sensors with various resistance values at 25 °C: 5k, 10k, 15k, and others.

 

Tab. 3. Tolerance for thermistors with a negative temeprature ceofficient

Maximum tolerance of resistance at 25 °C, R25	typically ± 3 %
The temperature range	- 45 ÷ + 125 °C

 

KTY 81-121 - a silicon temperature sensor with a positive temperature coefficient. A cheap resistance sensor with lower accuracy (the basic error is about ± 2 °C at ambient temperature).

 

Tab. 4. Detail information about the silicon temperature sensors

Nominal resistance R25	980 ÷ 1000 Ω
The temperature range	- 55 ÷ + 150 °C

 

TC - a thermocouple, a thermoelectric temperature sensor.

Thermocouples are mainly used for measuring very high temperatures, up to 2,300 °C; the sensors have poorer stability over time and very low sensitivity. .

Thermoelectric sensors are based on the Seebeck effect (converting thermal energy into electricity). A thermocouple consists of two wires of different metals with a conductive connection at each end. If the temperature t_m of the measuring junction differs from the temperature of the t₀ reference junction, small thermoelectric voltage occurs (only several dozens of mV). The reference junction should be constant at the temperature of t₀ in order for the sensor to work properly. Alternatively, the impact of the thermoelectric voltage of this junction should be compensated (using the so-called cold junction compensation, CJC). In order to connect the sensor with the system analogue input, compensation or thermocouple wiring is required.

Thermocouple wiring is made of the same material as the thermocouple itself. That is the reason why there are also types J, K, etc. Owing to this, no new thermocouples occur in other joints (e.g.on the terminals between the thermocouple and the subsequent cable). If we used an ordinary wire, the combination of the two different materials would result in creating another thermocouple, which would generate voltage in relation to the temperature of this joint. This voltage would be added to the voltage of the thermocouple itself, rendering the measured values worthless.

Compensation wiring is a cheaper substitution of thermocouple cables. The material is not identical with that of the thermocouple, and the compensation wiring maintains the same parameters as thermocouple cables, but only up to 200 °C (rarely to 260 °C).

The specific type of thermocouple and the mechanical design of the sensor must be addressed with respect to each specific application. This text has been compiled with the help of information thermoprozess.cz, where you will also find a specific selection of thermocouple sensors.

 

Tab. 5. Basic properties of thermocouples (the selection according to the module C-IT-0200I):

Type	Range	Usage
B	250 to 1,820 °C	Suitable for extremely high temperatures
J	-200 to 1,200 °C	Suitable for oxidation, reducing, inert atmosphere and vacuum.
K	-200 to 1,370 °C	Suitable for oxidation, reduction and inert atmosphere, not suitable for vacuum.
N	-200 to 1,300 °C	Suitable for frequent and great variations in temperature; it does not respond to the neutron flux (suitable for the nuclear industry).
R	-50 to 1,760 °C	Suitable in high temperatures, resistance against corrosion and oxidation.
S	-50 to 1,760 °C	-the same-
T	-200 to 350 °C	The most suitable sensor for measuring low temperature, it can be used in vacuum, oxidizing and reducing atmosphere.

 

Tab. 6. A summary table of the relation between the resistance of sensors and the temperature

Type of sensor	Pt1000	Ni1000	Ni1000	NTC 12k	KTY 81-121
Tk	3850	6180	5000	-	-
°C	Ω	Ω	Ω	kΩ	Ω
-20	921,6	893	913,5	98,93	677
-10	960,9	945,8	956,2	58,88	740
0	1000	1000	1000	36,13	807
10	1039	1055,5	1044,8	22,8	877
20	1077,9	1112,4	1090,7	14,77	951
25	1097,3	1141,3	1114	12	990
30	1116,7	1170,6	1137,6	9,8	1029
50	1194	1291,1	1235	4,6	1196
100	1385,1	1617,8	1500	0,95	1679
150	1573,3	1986,6	1799,3	-	2189
250	1941	2896,4	-	-	-

 

Tab. 7. Classification of temperature sensors according to the measuring technology

Measuring	Module on CIB		Independent sensor		RFox module		Note
Interior temperature	C-IT-0200R-design TXN 133 20	S-TS01R-design		-		The wall-mounted sensor, on customer's request
	C-IT-0200R-Time TXN 133 19.01	S-TS01R-ABB TXN 134 01.01		R-IT-0100R-Time		The wall-mounted sensor, the ABB Time design
	C-IT-0200R-ABB TXN 133 19.xx	S-TS01R-ABB1) TXN 134 01.xx		-		ABB design sensor (except for the Time), it must be specified
Outdoor temperature	C-IT-0100H-P TXN 133 16.11		P11PA				Sensor on the facade
The floor temperature			SK8NTC12k-2PS-xx				Sensor for underfloor heating regulation
Temperature of the solar heating circuit medium			SK2PA-2SS-xx				The cable temperature sensor mounted on a pipe in the circuit
Water temperature in the tank			SK8NTC12k-2SN-xx				The cable sensor inserted in the tank immersion sleeve
Water temperature in the piping	C-IT-0100H-P TXN 133 16.12	P15PA				Contact sensor, heating water and utility water, solar systems
	C-IT-0100H-P TXN 133 16.12	P13PA-xx		R-IT-0100H-A		Sensor with an immersion sleeve (installed inside a pipe)
Air temperature in the duct	C-IT-0100H-P TXN 133 16.0x		P12PA-xx				An internal pipe sensor, HVAC regulation, the length of the stem must be specified
Water temperature in the swimming pool	C-IT-0100H-P TXN 133 16.0x		P12PA-xx				A sensor in the immersion sleeve in the piping, the length of the stem must be specified
Boiler flue gas temperature	C-IT-0200I, TXN 133 09 + thermocouple sensor						Thermocouple sensor measured by the C-IT-0200I module

Notes:

1. For the ABB Tango design, a different variant of the sensor order no. should be used: TXN 134 02.01 (the standard version in white).

 

For an overview of modules and types of connectable temperature (and other analogue values) sensors, see the Tab. 8.

 

Tab. 8. An overview of the CFox and RFox modules for measuring temperature and analogue values (voltage, current, etc.)

The number in the table box shows, how many inputs of the selected module enable measuring the sensor or the signal in the appropriate column.