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Connect the calibration standard to the calibration test port.
Apply pressure to the next preferred verification pressure.
After the current reading stabilizes, enter the pressure value from the calibration source,
and click OK.
After all the static pressure markers have been set, determine if calibration is required. Return the
manifold to service before exiting Calibration mode if more calibration is not required.
11.1.3
Calibrating static pressure
A three- or five-point pressure method is used to calibrate the flow computer SP cell. Different
pressures are applied to the cell from a known, traceable source with resultant pressure values
entered into the flow computer using PCCU32 software.
IMPORTANT NOTE: The flow computer uses an absolute static pressure (SP) cell. Absolute
pressure measures the referenced pressure to a vacuum or sealed pressure. This differs
from a gauge cell which measures the referenced pressure to the atmosphere. Since the SP
cell is an absolute device, it always measures the true pressure, relative to a vacuum or
sealed chamber. As such, when vented, it measures the true barometric pressure. For other
points of calibration, add the reading of the PSI and the barometric pressure to arrive at the
PSIA. Once this has happened, enter the reading.
11.1.3.1
Absolute vs. Gauge
The initial calibration point should be completed under vented conditions. Additionally, when this takes
place, ensure that the barometric pressure reading (in PSI) is used as the initial point.
When operating in PCCU32 Absolute mode, other points of calibration are determined by adding the
PSI reading and the barometric pressure to arrive at the PSIA. Enter this reading.
Operating in PCCU32 Gauge mode, the readings may be entered as read. Upon completion, a
barometric pressure reading is entered.
11.1.3.2
Calculating PSI
To convert barometric pressure measured in inches of mercury to PSI, perform the following
calculation:
Barometric Pressure (inHg inches of mercury) * 0.49115 = Barometric Pressure in PSI
11.1.3.3
Calibration
While performing the following procedures, wait for the flow computer display to stabilize before
entering the new values. If the flow computer is not in Calibration mode, the display will not
necessarily match the applied cell pressures.
Select Calibration on the tool bar to place the flow computer in Hold mode.
Select the measurement tube in the navigation tree.
On the Calibration tab, select SP from the Calibration drop-down menu.
Select either a 3- or 5-point calibration from the corresponding drop-down menu.
Select the range (URL) of the transducer SP pressure cell. The range should agree with the
tag attached to the transducer.
Define the SP display value: Absolute or Gauge.
IMPORTANT NOTE: Selecting Absolute will display the value with the barometric pressure
added in. If calibrating in Absolute mode, the barometric pressure is the low calibration
target point. Subsequent values require that the barometric pressure be added to the value
before the value is entered.
Selecting Gauge will display values in gauge pressure. Subsequent values require that the
entered values be in gauge pressure.
Enter the barometric pressure in the bottom field before proceeding.
Verify that the vent valve is closed.
Open both the high and low equalizer valves.
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