Reference Selection For Measuring By Means Of A Thermocouple; Difference Circuit / Average Value Circuit; Mains Frequency Filter / Measuring Frequency; Electric Damping - Siemens SITRANS TW 7NG3242 Betriebsanleitung

Functions / Operation by HART
series. Values of 0.1 to 10.0 for resistance thermometers as well as values from 1 to
10 for thermocouples can be set for the scaling factor.
Example: 3 x Pt500 parallel: Scaling factor = 5/3 = 1.67 (basis is Pt100)
4.2.6

Reference selection for measuring by means of a thermocouple

The connection type of the resistance thermometer for reference point measurement
for thermocouples can be selected. Use of the built-in Pt100 or an external Pt100
which is necessary when the measuring point is remote from the SITRANS T3K PA.
An external reference point terminal is available as an accessory under order number
7NG3092-8AV. Information about using and connecting the reference point terminal
on the SITRANS TW can be found in chapter 3.6, page 94.
4.2.7

Difference circuit / average value circuit

The difference and average value circuit connection have the following special
features in comparison with the other connections (standard, sum, parallel):
Set start of scale and full scale
• First enter the start of scale and full scale for the two single sensors. The start of
scale and full scale are identical for both sensors. Different measuring ranges
cannot be parameterized for the single sensors.
• Then the start of scale and full scale for the difference or average value must be
parameterized.
Sensor trimming
• The sensor trim is performed at the respective range limits of the two single
sensors. The parameterized difference or the parameterized average value
cannot be trimmed.
4.2.8

Mains frequency filter / measuring frequency

An interference suppression of the mains frequencies of 50Hz or 60Hz can be set
with this filter. 10 Hz can also be selected as a special function. The selected mains
frequency filter is equivalent to the measuring frequency used. If the 10 Hz mains
frequency is used, greater accuracy at the cost of lower measuring speed is possible.
4.2.9

Electric damping

The filter time constant of the electric damping can be set in the range from 0 to
100 s.
102
SITRANS TW
A5E00054075-05