Thermo Electron Polysonics SX40, User Manual

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Troubleshooting & Maintenance
General Troubleshooting
Thermo Electron Corporation Polysonics SX40 User Guide 6-3
Doppler flowmeters are often used in installations which use VFDs. VFDs
can cause significant noise, EMI, and voltage spikes. If there are spikes on
the 4–20 mA signal line while the displayed flow rate is stable, there are
two actions you can take. Both actions may be required in order to resolve
the problem:
1. Disconnect the 4–20 mA loop wiring and connect an ammeter with
short wires directly to the 4–20 mA terminal block. Monitor the meter
to see if the spikes are reduced. Installing a twisted pair shielded loop
wiring in grounded metal conduit may be required.
2. Disconnect power wiring from the meter and connect to an
uninterruptible power supply which is not connected to the facility
wiring. Monitor the 4–20 mA output to see if the spikes are reduced.
Installing the power mains in grounded metal conduit may be required.
1. From the Flow screen, select FFT.
2. Refer to Figures 6–1 through 6–6 to determine the FFT condition.
3. Refer to the table below to determine the corrective action.
4. Return to the Flow screen.
Table 6–4.
FFT Shape Possible Cause Corrective Action
Ideal Doppler N/A 1. Restart the meter.
Broadband noise Poor pipe coupling or multiple
noise generators 1. Refer to Table 6–1 and complete action codes A-D, checking the meter after
performing each action to see if the problem was corrected.
2. Relocate transducers.
3. Turn off source of noise.
Steady noise spike Electromagnetic noise 1. Turn off source of noise.
2. Relocate transducers.
Fluctuating Doppler Constantly changing flow or noise 1. Increase damping (reference “Configuration” in chapter 3).
2. Relocate transducers.
No Doppler reflection
I or II
Ultrasound signal not transmitting 1. Refer to Table 6–1 and complete action codes A-D, checking the meter after
performing each action to see if the problem was corrected.
Variable Frequency
Drives (VFDs)
Checking the FFT