KROHNE OPTITEMP TT 10 C-R EN - Manual (Page 42)

7
TECHNICAL DATA
42
OPTITEMP TT 10 C/R
www.krohne.com 02/2013 - 4000752703 - MA OPTITEMP TT 10 C/R R03 en
7.1.2 Thermocouples
The thermocouple features two electric conductors made from different metals, connected at
one end. Each free end is connected to a compensation cable extension or direct connected to a
millivolt meter. This circuitry forms a "thermal circuit". The point at which the two electric
conductors connect is called the measuring point or hot junction and the point at which the
compensation cables connect to the conductors of the millivolt meter is called the cold junction.
If the measuring point of this thermal circuit is heated up, a small electrical voltage (thermal
voltage) can be measured. If, however, the measuring point and the cold junction are at the same
temperature, no thermoelectric voltage is generated. The degree of thermoelectric voltage, also
known as electromotive force (EMF), depends on the thermocouple material and the extent of
the temperature difference between the measuring point and the cold junction. It can be
measured using the millivolt meter with no auxiliary power.
Compensation cable has the same thermoelectric behavior as the thermocouple in a limited
temperature range.
Extension cable is a thermocouple but designed as an installation cable.
Simply put, the thermocouple behaves like a battery, the voltage of which also increases as the
temperature rises.
INFORMATION!
The characteristic curves and tolerances of commercially available thermocouples are
standardised in IEC 60584.
Figure 7-2: Thermocouple measuring circuit, schematic.
1 Measuring point t 1
(hot junction)
2 Thermocouple
3 Transition junction t
2
4 Compensation cable / extension cable
5 Reference junction t
3
(cold junction)
6 Copper conductor
7 Voltage meter U
th
.book Page 42 Tuesday, February 26, 2013 1:43 PM