Eaton ELCM Series, Руководство по эксплуатации

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E L C O p e r a t i o n M a n u a l
F o r m o r e i nf o r m a t i o n v i sit :
w w w. e a t o n . c o m
MN05003006E 1-156
3.2.5 ELCM-TC04ANNN
3.2.5.1 The Thermocouple Temperature Sensor
A thermocouple is composed of conductors of two different materials. When a temperature
difference occurs at the two ends of the thermocouple, the thermocouple will generate a voltage
signal in proportional to the temperature difference. The voltage signal ranges from tens of uV to
thousands of uV; therefore, we need to magnify the voltage when using it.
The thermocouple temperature sensor indicates temperature by differential voltage, and this
eliminates external interferences the two pairs of data are a differential operation. Therefore, it is
much more stable than a thermistor, resistive thermometer or thermal resistor and is widely
applied in the industry.
The thermocouple is a loop constructed by two different metallic wires welded or twisted together
(see the figure below). Different metals make two junctions in the loop. One junction is called
“measuring junction” or “hot junction”, and the other is “reference junction” or “cold junction”.
Placing the two junctions in different temperatures will cause a loop voltage (i.e. Seebeck Effect),
and the loop voltage is in proportional to the temperature difference between the two junctions.
The loop voltage and the two junctions’ equation:
( )
∫
− =
2
1
T
T
B A
dT Q Q V
(A)
In which Q = the heat conduction coefficient of the metal
How a thermocouple works
The heat conduction coefficient of Q
A
and Q
B
has nothing to do with the temperature. Therefore,
equation (A) can be simplified into equation (B), a more frequently used equation:
V = α (T
2
-T
1
)
(B)
There are two types of thermocouples, wrapped thermocouple and bare thermocouple. The
wrapped thermocouple is wrapped with a layer of metal for protection, similar to an
electrically-heated spoon. The wrapped thermocouple is used for measuring temperature of
liquid and the bare thermocouple is used for measuring gas temperature. Different
thermocouples sense different temperature ranges and output signals, and the maximum
temperature varies with different materials and wires of different diameters.
3.2.5.2 Introduction
The ELCM-TC04ANNN temperature measurement module contains 4 inputss for external
thermocouple temperature sensors (J-type, K-type, R-type, S-type, T-type, E-type, N-type,
±80mV). It converts them into 16-bit digital signals. Select temperatures in Celsius (resolution: