ACS-CONTROL-SYSTEM GmbH
l Lauterbachstr. 57 l D-84307 Eggenfelden l www.acs-controlsystem.de l [email protected]
14
5 .5 Self-supervising function
5 .5 .1 Drift monitoring function
The drift monitoring function is only adjustable at devices with option self-supervising.
Each sensor element that is used for the recording of temperatures has the unavoidable characteristic
a specific behavior concerning long term drift and ageing.
This behavior is very similar if not identically at physically equal-type sensor elements like e.g.
multiple resistive sensors Pt100.
At physically different sensor elements like resistive sensors Pt100 and semiconductor sensors or also
NTC however these characteristics are serious different.
In the tip of the sensor tube are two physically different sensor elements mounted thermal coupled.
For the realizing of a reliable drift supervising a different drift behavior of the two sensor elements is
necessary.
Therefore e.g. not two resistive sensors Pt100 are uses, but only one resistive sensor element Pt100
and a semiconductor sensor element.
Under nominal conditions the temperature measuring values, which are recorded by the sensor
elements and transmitted to the processor are identically. Because of the not exactly identical position
of both sensor elements within the sensor tube, the installation position of the sensor tube and the
present process conditions temperature differences of up to ±0,1K can occur, already at a new device.
This does not affect the function of the drift supervision concerning ageing.
Because of the use of two physically different sensor elements it is guaranteed, that the ageing
conditioned characteristic drift of both sensor elements is different. At the occurring of an ageing
conditioned characteristic drift in one or also in both sensor elements the difference between the
temperature measuring values of both sensor elements increases.
The detected difference between the temperature measuring values is compared with the set drift
response value (
drAL
) by the processor.
If the temperature difference between the temperature measuring values transgresses the set drift
response value (
drAL
), the drift alarm will be registered in the error memory (
ErrN
), the red error
indication LED starts flashing and the switch output 1, if configured for error function, will be activated
corresponding to the settings in normally open or normally closed function.
The display and the current output generate furthermore a temperature proportional signal, referring
to the temperature measuring value of the primary sensor element, the resistive sensor Pt100. The
switch outputs, which are configured for normal function, refers also to this temperature measuring
values.
Because of the different response time of the two sensor elements, at fast and strong temperature
fluctuations in the measured medium, e.g. at filling a hot medium in a cold container, it can come to
short time differences between the two temperature measuring values that are higher than the set
drift response value (
drAL
).
A wrong drift alarm would be detected.
For the compensation of such wrong behaviors a drift delay time (
drd
) can be set.
Due to this a drift alarm will only be detected, if after the transgression of the drift response value
(
drAL
) and after the set drift delay time (
drd
) the set drift response value (
drAL
) is already
transgressed.
5 .5 .2 Redundancy function
The redundancy function is only adjustable at devices with option self-supervising.
The display, the switching output resp. outputs and the current output refers principally to the
temperature measuring value of the primary sensor element, the resistive sensor Pt100.
In the case of a short circuit or a wire break of the primary sensor element, the resistive sensor Pt100
there is the possibility to continue the measurement automatically with the secondary sensor element,
the semiconductor sensor.
The display, the switching output resp. outputs and the current output refers now to the temperature
measuring value of the secondary sensor element, the semiconductor sensor.
A drift monitoring is not possible in the case of the failure of one of the two sensor elements.
The behavior of the temperature switch in the case of the failure of the primary sensor Pt100 resp. the
activation of the redundancy function is made by the parameter (
drb
).
Summary of Contents for Thermocont TS4S
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