a customized pressure span of 4 psi and offset of 12 psi can be configured from a 20 psia device by
using the offset (
O=
) and window (
W=
) commands. First, set the window offset to
O=60
so that the
lowest analog output would begin at 12 psi (60% of 20 psi). Then, set the window width to
W=20
so
that the pressure span is 4 psi (20% of 20 psi). The pressure range vs. output level curve is shown in
Figure 4.5.
4.85
1
Analog Out (V)
AN=ON
4.85
1
Analog Out (V)
AN=ON
Pressure (psi)
20
Pressure (psi)
12
16
20
Figure 4.4—User Modified
Output Levels
Figure 4.5—User Modified
Pressure Span
Using the store parameters command (SP), the configuration changes can be saved in EEPROM
so that the PPT will power up in that state ready to operate. This is particularly useful for
applications that use the analog output signal. The PPT can be configured and stored in the lab
and used in the field as an analog only instrument.
4.6
CUSTOMIZED PRESSURE RANGE
The user can adjust the pressure vs. output value transfer curve using the
X=
,
Y=
,
Z=
and
F=
commands. The
X=
command adjusts the slope of the pressure output curve for positive pressures.
This applies to all absolute and gauge devices and modifies the positive full scale slope of PPTs. The
Y=
command adjusts the negative full scale slope of differential PPTs. The
Z=
command adjusts the
offset of the pressure output curve. The range of adjustment for
X=, Y=
and
Z=
commands is
±0.6%FS in 0.005% increments. The
F=
command can change the full scale pressure span to any
value between 50% and 100% of the factory specified range (
M=
).
The purpose of these commands is to allow the user to provide compensation for the pressure values
specific to an application. This type of adjustment is made after the PPT temperature compensates
the pressure reading according to the factory calibration. The user supplied values (
X=
,
Y=
,
Z=
) are
used as an mx+b correction. The
X=
and
Y=
command supplies the slope adjustment, or ‘m’, value
and the
Z=
command supplies the offset adjustment, or ‘b’, value. Figures 4.6 and 4.7 illustrate these
commands.
5
Analog Out (V)
+0.6%FS Slope=1
-0.6%FS
20
Pressure (psi)
5
Analog Out (V)
+0.6%FS
Offset=0
-0.6%FS
20
Pressure (psi)
Figure 4.6—Custom Slope (X=) Options
1 7
Figure 4.7—Custom Offset (Z=) Options
