Keba Kemro TM 220/A, Руководство по проектированию устройства

Страница: 18 / 27

6 Functional description
6.1 General functions for measuring temperatures with thermocou-
ples
6.1.1 Principle of temperature measurements
Fig.6-1: Temperature measurement
The thermocouple supplies (active) a voltage U
θ
, which depends on the tem-
perature difference between the measuring point (w) and the comparison point
(u, terminal). k is the temperature coefficient of the thermocouple. It is de-
pendent on the material and the temperature. Therefore a change in the
thermo-voltage is not proportional to the temperature change. The software
executes the linearization.
To enable evaluation of the temperature at the measuring point, the tempera-
ture of the comparison point must be known. The latter is measured by a
terminal temperature sensor that is integrated into the module.
6.1.2 Temperature data sampling
Fig.6-2: Block diagram
1 ... Counters and logic
The thermo voltage at the input terminals is amplified and converted into a
proportional frequency in the voltage-to-frequency converter. The measure-
ment period lasts 100 ms.
Due to the integrating measurement procedure used, any interference that oc-
curs at the AC line frequency (50 Hz, 60 Hz) is filtered out.
Functional description TM 240/A, TE 220/A for KeStudio U3
© KEBA 2011
Project engineering manual V1.10 18