User`s guide

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CHAPTER 6 - DETAILED PARAMETER DESCRIPTION
2)
Feedback (process variable measurement): the feeback
is always realized via analog inputAI1.
Transducer (sensor) to be used for the feedback of the
control variable: itis recommended to use a sensor with
full scale with at least 1.1 times higher than the largest
value of the process variable that shall be controlled.
Example: if a pressure control at 20 baris desired,select
a sensor with a control capacity of at least 22 bar.
Signal type: set P235 and the position of the switch S1
on the control board according to the transducer signal
(4 -20 mA, 0 -20 mA or 0 -10 V).
Set P234 and P236 according to the variation range of
the used feedback signal (for more details, refer to
description of the parameters P234 to P240).
Example: suppose the following application:
-
Full scale of the transducer (maximum value at the
transducer output) = 25 bar (FS = 25).
-
Operation range (range of interest) = 0 to 15 bar
(FO = 15).
Considering a safetymargin of 10 %, the measuringran-
ge of the process variable must be set to: 0 to 16.5 bar.
Thus: FM = 1.1 x FS = 16.5.
Parameter P234 must be set to:
P234 =
FS
=
25
= 1.52
FM
16.5
As the operation range starts at zero, P236 = 0, thus a
setpointof 100 %represents 16.5 bar,i.e., the operation
range, in percentage, is within: 0 to 90.9 %.
NOTE!
In the most cases it is not necessary to set the gain and the
offset (P234 = 1.00 and P236 = 0.0). Thus the percentage
value of the setpoint is equivalent to the percentage value of
the full scale of the used sensor. However if the maximum
resolution of the analog input AI1 (feedback) is desired, set
P234 and P238 according to comments above.
Setting of the display indication to the process variable
measuring unit (P040): set P528 according to the full scale of
the used transducer (sensor) and defined P234 (refer to the
description of parameter P528).