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Configuration and Use Manual 37
Calibration
Startup ConfigurationCalibrationBefore You Begin
3.6 Performing zero calibration
Zeroing the flowmeter establishes the flowmeter’s point of reference when there is no flow. The meter
was zeroed at the factory, and should not require a field zero. However, you may wish to perform a
field zero to meet local requirements or to confirm the factory zero.
When you zero the flowmeter, you may need to adjust the zero time parameter. Zero time is the length
of time the transmitter takes to determine its zero-flow reference point. The default zero time is
20 seconds.
•A long zero time may produce a more accurate zero reference but is more likely to result in
zero failure. This is due to the increased possibility of noisy flow, which causes incorrect
calibration.
•A short zero time is less likely to result in a zero failure but may produce a less accurate zero
reference.
For most applications, the default zero time is appropriate.
Note: Do not zero the flowmeter if a high severity alarm is active. Correct the problem, then zero the
flowmeter. You may zero the flowmeter if a low severity alarm is active.
If the transmitter is connected to an enhanced core processor, there are two recovery functions that
may be used if the zero procedure fails:
• Restore prior zero – Available only from ProLink II and only during the current zero
procedure. Once you have closed the Calibration dialog box or disconnected from the
transmitter, you can no longer restore the prior zero.
• Restore factory zero – Always available via all configuration tools.
Note: If the flowmeter fails the zeroing procedure twice, refer to Section 6.6.
3.6.1 Preparing for the zeroing procedure
To prepare for the zeroing procedure:
1. Apply power to the flowmeter. Allow the flowmeter to warm up for approximately 20 minutes.
2. Run the process fluid through the sensor until the sensor temperature reaches the normal
process operating temperature.
3. Close the shutoff valve downstream from the sensor.
4. Ensure that the sensor is completely filled with fluid and the flow through the sensor has
completely stopped.
If fluid is flowing through the sensor, the sensor zero calibration may be inaccurate, resulting in
inaccurate process measurement. To improve the sensor zero calibration and measurement accuracy,
ensure that process flow through the sensor has completely stopped.
3.6.2 Zeroing procedure
To zero the flowmeter:
• With the EDD, refer to the menu flowchart in Figure 3-9.
• With bus parameters, refer to the menu flowchart in Figure 3-10.
• With ProLink II, refer to the menu flowchart in Figure 3-11.
• With the display, refer to the menu flowchart in Figure B-17.