FISCHER DE49 A Series, Operating Manual

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4 | Commissioning FISCHER Mess- und Regeltechnik GmbH
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After setting all parameters, leave the menu as follows:
• Use the arrow keys
ÿ þ
to set the
ESc
parameter. You will find these at
the start and also at the end of the menu.
• Press the enter key
û
to leave to the menu.
4.3.1 Zero point control and adjustment
Ensure that the device is not pressurised (if necessary, disconnect any pressure
lines). If the device does precisely indicate zero at this point of time, parameter
0ff
enables you to adjust the measuring value exactly to zero.
After zero-point adjustment, any disconnected pressure sensing lines can be re-
connected.
4.3.2 Damping and zero-point stabilising
If there are unsteady pressure readings at this point of time or during operation,
you can use parameters
dam
and
nP
to stabilise the reading (and the output
signal).
The parameter
dam
functions like a capillary throttle. However, it only acts on
the display and output signal but not on the measuring cell itself. You can set
the response time to pressure jumps with this parameter. The value range is 0.0
s to 200.0 s.
NOTICE
Maximum damping
But with maximum damping, it will take more than 2 minutes for the reading also
to reach zero after a pressure jump from nominal pressure (100 %) to zero!
In many cases, unsteady readings are not a problem during normal operating
mode, but this is not true for the idle state, i.e. if zero (differential) pressure is
expected.
In such situations, parameter
nP
can be used. Its value defines a range of
measurement range around zero. The measured value is set to zero within this
range.
Measured value
Display value
np
Zero-point window
np
2x -
np
2x -
np
Fig. 9: Zero-point window
Example:
A value of 0.08 mbar is entered for
nP
. In this case all pressures within the
range of -0.08 mbar to +0.08 mbar are set to zero on the display. The reading
will only not indicate zero any more if the pressure exceeds these limits. How-
ever the pressure value and display do not correspond to one hundred percent.
The measuring pressure and reading match again when the double value, in
this case 0.16 mbar, is reached again.