ABB XSeriesG4 User Manual page 129

Important Note: The flow computer uses an absolute static pressure (SP) Cell. Absolute pressure measures the
pressure referenced to a vacuum or sealed chamber. This is different than a gauge cell which measures the
pressure referenced to the atmosphere.
Since the static pressure cell is an absolute device, it always measures the true pressure relative to a vacuum or
sealed chamber. When vented, it measures true barometric pressure.
For other points of calibration, add reading of PSI and barometric pressure to arrive at PSIA, then enter this
reading.
6.13.5.1 Absolute vs. Gauge
It is recommended that the initial calibration point be at vented conditions. When doing so the barometric pressure reading (in
psi) may be used as the initial point.
When operating in PCCU's Absolute Mode, other points of calibration are arrived at by adding the PSI reading and barometric
pressure to arrive at PSIA, then enter this reading.
When operating in PCCU's Gauge Mode, readings may be entered as read, then a barometric pressure reading is entered.
IMPORTANT NOTE: To convert barometric pressure measured from inches of mercury to Barometric Pressure
(psi), perform the following calculation:
Barometric pressure, in inches of mercury x .4912 or (  2.036) equals Barometric Pressure in psi.
6.13.5.2 Calibrating Static Pressure (SP)
Equipment needed:
-Calibration standard
To calibrate Static Pressure (SP):
Connect the PC running PCCU32 to the flow computer with either an MMI cable (RS-232), a USB cable or an
Ethernet cable.
Open PCCU.
Select the Calibration button from the toolbar. The flow computer is placed in hold.
Select the desired measurement tube from the tree view in the left pane.
Select SP from the calibration drop down box to the left of the pressure marker table.
Select the 3 or 5 Point Calibration.
Set the Transducer SP Pressure Range in calibration window. This should match the range reading from the tag or
label attached to the transducer.
Select the SP type: Absolute or Gauge.
IMPORTANT NOTES: Absolute will display values with Barometric Pressure added in plus entered values will
need the Barometric Pressure added.
Gauge will display values in Gauge Pressure plus entered values will need to be in Gauge Pressure.
Enter the barometric in the bottom window before proceeding.
Verify that the vent valve is closed (Figure 92:).
Open both the high and low equalizer valves.
Close both the downstream and upstream tap valves.
Open the atmosphere vent valve.
Click on the Low Cal Point button.
Verify the Current Reading is Continuously updated. This should represent the lowest calibration point.
130 XFC G4 2103335 Rev AB