Emerson Process Management MICRO MOTION 2400S - Manual (Page 107)

Configuration and Use Manual 99
Measurement Performance
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Compensation
10.5 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
amount 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 a
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. See Section 7.5 for
information on viewing transmitter status and alarms.
If the zero procedure fails, two recovery functions are provided:
• Restore prior zero, available only from the Calibration dialog box in ProLink II (see
Figure B-1), and only if you have not closed the Calibration window or disconnected from the
transmitter. Once you have closed the Calibration window or disconnected from the
transmitter, you can no longer restore the prior zero.
• Restore factory zero, available via:
- The display – see Figure B-7
- ProLink II – see Figure B-1
- A DeviceNet tool – use the Diagnostics Object (0x66), Instance 1, Service 0x52. For more
information, see the manual entitled Micro Motion Model 2400S Transmitters
for DeviceNet: Device Profile.
If desired, you can use one of these functions to return the meter to operation while you are
troubleshooting the cause of the zero failure (see Section 11.8).
Example The flowmeter is installed and proved for the first time. The flowmeter
mass measurement is 250.27 lb; the reference device measurement is
250 lb. A mass flow meter factor is determined as follows:
The first mass flow meter factor is 0.9989.
One year later, the flowmeter is proved again. The flowmeter mass
measurement is 250.07 lb; the reference device measurement is
250.25 lb. A new mass flow meter factor is determined as follows:
The new mass flow meter factor is 0.9996.
MassFlowMeterFactor 1
250
250.27
------------------
×
0.9989 = =
MassFlowMeterFactor 0.9989
250.25
250.07
------------------ Ч
0.9996 = =