IDL 101
FUNCTIONAL DESCRIPTION
HB_IDL101_E_V222.doc
41
Gantner Instruments Test & Measurement GmbH
Thermocouples consist of two "thermoelectric wires" made of different materials (e.g. platinum and platinum rhodium)
that are welded to each other at one end. If the contact position and the other ends of the thermoelectric wires have
different temperatures, a "thermoelectric voltage" U
th
appears at the contact position of both thermoelectric wires. This
voltage is largely proportional to the temperature difference. It can be measured and can be used for temperature
measurement purposes. With the
Datalogger IDL 101
the thermoelectric voltage is measured differentially.
Since thermocouples can only measure a temperature difference (difference between temperature to be measured and
temperature at the connecting terminals on the sensor module), a terminal temperature or a known temperature
reference also have to be determined. In the first case this is called internal cold junction compensation (TC
int
), in the
second case external cold junction compensation (TC
ext
).
At the measuring of temperature with internal cold junction compensation by means of cold junction terminals
ICJ 104
,
where a Pt100 temperature sensor is integrated directly in the terminal block, the temperature
ϑ
k
will be entered. The
temperature of the test point determines the data logger because of linearization trace to
ϑ
x
= Lin(U
x
+Lin
-1
ϑ
k
).
If the temperature is measured by external cold junction compensation, a second thermocouple of the same type is
required, which is connected in series with the first one. The polarity is selected so that the thermoelectric voltages
subtract each other. The second thermocouple is set to a fixed reference temperature
ϑ
r
(mostly
ϑ
r
= 0°C). The sensor
module then calculates the temperature at the measuring position by means of the linearization curve as
ϑ
x
=
Lin(U
x
+Lin
-1
ϑ
r
). The sensor module will be informed about the reference temperature
ϑ
r
via the
Configuration Software
ICP 100
("cold junction temperature").
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