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Configuration and Use Manual 39

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5.5 Zeroing the flowmeterZeroing the flowmeter establishes the flowmeters point of reference when there is no flow. The meterwas zeroed at the factory, and should not require a field zero. However, you may wish to perform afield 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 theamount of time the transmitter takes to determine its zero-flow reference point. The default zero timeis 20 seconds.

A long zero time may produce a more accurate zero reference but is more likely to result in azero failure. This is due to the increased possibility of noisy flow, which causes incorrectcalibration.

A short zero time is less likely to result in a zero failure but may produce a less accurate zeroreference.

For most applications, the default zero time is appropriate.

Note: In some menus, a convergence limit parameter is displayed. Micro Motion recommends that youuse the default value for convergence limit.

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. See Section 7.5 forinformation on viewing transmitter status and alarms.

If the zero procedure fails, see Section 12.6 for troubleshooting information. Additionally, if you havethe enhanced core processor:

You can restore the factory zero. This procedure returns the zero value to the value obtained atthe factory. The factory zero can be restored with ProLink II or the display (if the transmitterhas a display).

If you are using ProLink II to zero the flowmeter, you can also restore the prior zeroimmediately after zeroing (e.g., an undo function), as long as you have not disconnectedfrom the transmitter. Once you have disconnected from the transmitter, you can no longerrestore the prior zero.

5.5.1 Preparing for zeroTo prepare for the zero 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 normalprocess operating temperature.

3. Close the shutoff valve downstream from the sensor.

4. Ensure that the sensor is completely filled with fluid.

5. Ensure that the process flow has completely stopped.

CAUTIONIf fluid is flowing through the sensor, the sensor zero calibration may beinaccurate, resulting in inaccurate process measurement.

To improve the sensor zero calibration and measurement accuracy, ensure thatprocess flow through the sensor has completely stopped.

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Figure 5-5 Display menu Flowmeter zero procedure

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OFF-LINE MAINT

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CAL ZERO

ZERO/YES?

CAL PASSCAL FAIL

EXIT

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ZERO

Troubleshoot

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RESTORE ZERO (1)Scroll

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RESTORE/YES?

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(1) Available only on systems with the enhanced core processor.