FISCHER DE44, Operating Manual

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The difference between values
MA
and
ME
must at
least be 25 % of the basic measuring range. The
software does not allow any larger spreads. If the
range information is stated wrongly, you cannot
leave the menu.
Example:
The following must apply for a basic measuring
range of 400 Pa:
MA
–
ME 
100 Pa.
5.3.7 Output signal limits (Namur)
Regardless of the pressure, the three parameters
oG1
,
oG2
and
oEr
define the limit values for output
currents or voltages that may not be undercut or
exceeded.
These limit values have priority over the range de-
fined by the
MA
and
ME
. They primarily serve to pre-
vent error messages in downstream systems
caused by brief overstepping of measuring ranges.
The parameter
oG1
defines the limit value for the
minimum output signal. The output signal may not
undercut this value. Usually, this parameter is only
recommended for devices with an output signal of
4..20 mA because in these devices, a value below
3.8 mA is often assessed as an error signal.
The parameter
OG2
defines the limit value for the
maximum output signal. The output signal may not
exceed this value. This parameter can be used for
all outputs (voltage and current) to limit the maxi-
mum value of e.g. 10.2 V.
The parameter
oer
defines the value for the error
signal. The value defined via the
oEr
is issued as an
output signal, if the device detects an internal error
and can no longer work correctly. However, the de-
vice is not able to recognise all possible errors and
defects.
If you set
oG1
=
OG2
= 0, the output signal will no
longer be checked for limits.
If you set
oG1
to the maximum value (11
V or 21 mA), you can use
OG2
to adjust
the output signal independent of the
pressure from zero to the maximum value. You do
not need to leave the menu item, the output is di-
rectly changed. You operate the device then as a
transducer and can simply check the further signal
processing.
5.3.8 Characteristic curve function
F
In some applications, measuring pressure is an in-
direct unit for the actual measuring variable. Flow
measurements via a panel or determining the filling
level by means of hydrostatic pressure measure-
ments are two typical examples of this. In these
cases, you might want to change the output signal
of the transmitter to a non-linear characteristic
curve so that the following analysis receives a sig-
nal that is linear-proportional to the actual measur-
ing variable (e.g. volume in m³ or volume flow cm³/s
etc.)
The parameter
F
allows you to select between the
following variants:
F
0 linear characteristic curve (standard)
1 square rooted characteristic curve
2 flat cylindrical tank
3...30 Support point table with 3 to 30 pairs of values
Whenever you change the value from
F
, the pro-
gram creates a new table. All previous values in the
table are rejected and replaced with new linear en-
tries.
The tables of type
F
= 0 to
F
= 2 are not visible. In-
ternal values are used here to calculate the table.
These values are invariable.
For
F
= 3...30, you can only influence the 1..28 inter-
im values. You only have access to the start and
end values via the
MA
and
ME
parameters (cf. 5.3.6).
When the parameters
MA
and
ME
are
changed the table is deleted and
F
= 0 is
set.
At the start of the measuring range (
MA
) 0% of the
output signal (e.g. 0 mA) is issued.
At the end of the measuring range (
ME
) 100% of the
output signal (e.g. 20 mA) is issued.
5.3.9 Menu jump
LIN
If the value of
F
is greater than or equal to 3, there
is a submenu
LIn
. Here you can access all table
values apart from the table start (
MA
) and end (
ME
).
This submenu has its own entry and exit point that
is shown with
End
. The table is only saved if you re-
turn to the main menu at this point, i.e. if you
change to the parameter
LIN
again via the key
û
.
If the table is not structured correctly, an error mes-
sage
Err
will appear here and you cannot quit the
submenu.
The table comprises 3…30 pairs of values. In the
case of a device with a power output, the first pair
of values is {
I01
|
P01
} 4 . The first value
I01
defines the
output signal. The second value
P01
determines the
pressure at which the output signal is issued.
Followed by the pairs of values {
I02
|
P02
} ... {
I30
|
P30
}.
Entering or changing values in the table via the
membrane keypad is tiresome and prone to errors.
This is only intended as an emergency solution in
case access to the PC adapter is not possible.
4
At a voltage output {
u01
|
P01
} ... {
u30
|
P30
}.