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Model 7000 Series Turbine Flowmeter Section 3

ElectricalPickupCoilCheck

Items Needed: Ohmmeter and Oscilloscope

1. With an ohmmeter, measure the resistance between the pickup pins. The

resistance should be approximately 1200 ohms.

2. Measure the resistance between each pin and the pickup coil housing.

The resistance should be at least 100 megohms.

3. If either of the above readings are not as specied, replace the pickup

coil.

4. Connect an oscilloscope to the pickup coil. Check the signal-to-noise

ratio by comparing the peak-to-peak voltage while running the meter at

the minimum ow rate versus the peak-to-peak voltage at no ow. The

ratio shall be in the area of 20:1 or higher.

If the signal-to-noise ratio is not as required, examine the immediate area

for either radiated or conducted type of electrical interference. Minimize

the electrical interference by removing the source of the interference or

by reorienting the meter.

The most effective method of locating the source of electrical interfer-

ence is to turn off the power to electrical machinery or electronic devices

one item at a time, and observe the change in amplitude of the interfer-

ence signal.

IMPORTANT: A low signal-to-noise ratio can feed deceptive information to the elec-

tronic instrumentation of the system. The addition of a preamplier at the

turbine meter will provide improved signal-to-noise ratio.

Troubleshooting

Turbine meter system malfunctions are usually restricted to two areas: electri-

cal/electronic, or mechanical.

When a malfunction or an apparent malfunction occurs, the electrical/elec-

tronic systems should rst be thoroughly checked in accordance with the

manufacturer's recommended procedures, prior to checking the turbine meter.

Only when the source of the malfunction cannot be found in the electrical or

electronic systems should the turbine meter be inspected.

IMPORTANT: Before performing any troubleshooting, refer to information, instructions,

and Warning/Caution notices in Sections 2 and 3.

Sensia Barton 7000 Series User Manual

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