Panametrics PanaFlow MV80, Руководство пользователя, Страница: 148 / 184

Chapter 5. Troubleshooting and Repair
136 PanaFlow™ MV80, MV82 & MV84 User’s Manual
5.5 Determine the Fault
5.5.1 Symptom: Output at No Flow
• The low flow cutoff is set too low. At no flow, go to the first column of the hidden diagnostics menu and record
the Lvl value. The low flow cutoff must be set above this value.
• Example: at no flow, Lvl = 25. Set the low flow cutoff in the Calibration Menu to approximately 28 and the meter
will no longer read a flow rate at no flow.
5.5.2 Symptom: Erratic Output
• The flow rate may be too low, just at the cutoff of the meter range, and the flow cycles above and below the
cutoff making an erratic output. Consult the factory if necessary to confirm the meter range based on current
operating conditions. It may be possible to lower the low flow cutoff to increase the meter range. See the
example above for output at no flow, only this time the low flow cutoff is set too high. You can lower this value to
increase the meter range as long as you do not create the output at no flow condition previously described.
• Mechanical installation may be incorrect. Verify the straight run is adequate, as described in Chapter 2 . For
in-line meters, make sure the meter is not installed backwards and there are no gaskets protruding into the
flow stream. For insertion meters, verify the insertion depth and flow direction.
• The meter may be reacting to actual changes in the flow stream. The output can be smoothed using a time
constant. The displayed values can be smoothed using the time constant in the Display Menu . The analog
outputs can be smoothed using the time constant in the Output Menu . A time constant of 1 will result in the
change in value reaching 63% of its final value in one second. A time constant of 4 is 22%, 10 is 9.5% and 50 is
1.9% of the final value in one second. The time constant equation is shown below (TC = Time Constant).
% change in final value in one second 100 1 e
-1 TC

–
 
=
• The vortex coefficient Ck may be incorrectly set. The Ck is a value in the equation used to determine if a
frequency represents a valid vortex signal given the fluid density and signal amplitude. In practice, the Ck value
controls the adaptive filter, fi , setting. During flow, view the f and fi values in the first column of the hidden
diagnostics. The fi value should be approximately 10-20% higher than the f value. If you raise the Ck setting in
the Calibration Menu , then the fi value will increase. The fi is a low pass filter, so by increasing it or lowering it,
you can alter the range of frequencies that the meter will accept. If the vortex signal is strong, the fi value will
increase to a large number - this is correct.