Niagara 6600 Series, Installation, Operation & Maintenance Manual

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NIAGARA Installation, Operation & Maintenance Manual M600
Rev. E 4
For any electromagnetic flowmeter to work reliably, it is therefore extremely important that the measuring tube is
completely full, which by default can be achieved easily through vertical mounting of the flowmeter. Hence a vertical
upstream installation is preferred.
Electromagnetic flowmeters can be installed in vertical, angle or horizontal mounting positions, as long as the pipe
remains completely full. The electrode axis in such installations must be kept in the horizontal plane.
To increase the signal to noise ratio, the magnetic field is pulsed. During the pulse period, voltage is induced at the
electrodes. During the off period, the generated voltage is zero. During this off pulse, any signal voltage is
interference (noise). This voltage is subtracted out and stored by the electronic circuitry (auto zero). During the
pulse period the stored interference voltage noise is subtracted and cancelled out by the electronics circuitry yielding
only the true generated signal that is being induced by the fluid moving through the meter. The auto zero occurs
several times a second insuring an automatic positive reference as to zero flow.
The induced voltages are amplified using differential amplifiers with high input impedances to minimize the effect
from any electrode coating. The amplifier gain is adjusted using R-ref in such a way that the flowmeter gives a 20
mA output current for maximum flow range. The current output can be used for remote indication and or recording
purposes.
To compensate for any fluctuations of the magnetic field intensity, the current passing through the coils is measured.
The magnitude of this current increases or decreases the frequency output on the amplifier card. This frequency is
used to generate the 4-20 mA current output. Pulse Outputs and Relay Outputs corresponding to High and Low
Alarms are generated by the micro controller.
All program data is stored in NVRAM. Even in the case of power failure, programmed parameters are retained by
the NVRAM.
Data entry is accomplished by activating Hall Effect switches using a magnetic commander.