Temperature Measurements - T/C's; Ranges And Linearization - Intab PC-Logger 2100 User Manual

2.2

Temperature measurements - T/C's

The "2100" is specially adapted for temperature measuring using thermocouples.
The high resolution of the A/D converter makes it possible to record
temperatures in excess of 1000°C with a resolution of 0.1°C using
thermocouples of type "K".
Thermocouples are active sensors that don't require powering to supply a signal.
They are highly non-linear but are linearized by the "2100".
A thermocouple is, in its simplest form, a pair of wires of dissimilar metals that
are soldered together at one end. The other end is connected to the two screw
terminals of a channel. The difference in temperature between the soldered end
and the screw terminals gives rise to a voltage that can be measured.
This voltage is different for different thermocouple materials. Simply "tell" the
software which type(s) you are using by specifying J, K, T; S, R or ...etc. for
each channel before starting a recording.

2.2.1 Ranges and linearization

Different types of thermocouples have differing levels of output. They therefore
have differing fields of application most often depending on the temperature
range to be measured.
What two materials make up the couple may also be of a certain importance. We
will however have to assume that this is known to the user.
Below is a short summary of the properties of the most common types of
thermocouples. It is included to help in selecting type and range for your
application. "K" is the most common type.
"Cold Junction" = 0°C
TYPE
K
J
T
S
R
Thermocouples are highly un-linear. This is corrected by the internal program of
the "2100".
Thermoelectric voltage is measured (in mV) and then adjusted for the cold
junction temperature according to the type specified. This adjusted voltage is
then used as input variable to a linearizing table. The table (one for each
thermocouple type) is constructed so that its contribution to the measurement
error is negligible.
(+/-0.05°C for T<250°C; +/-0.15°C for T>250°C and "K"-type)
mV at mV at
200°C 600°C
8.137 24.902
10.777 33.096
9.286 ---------
1.440 5.237
1.468 5.582
2 ANALOGUE INPUTS / RANGES
mV at
1200°C MAX temp °C
48,828 1370
---------- 760
---------- 400
11.947 1760
13.224 1760
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