Magnet Coil Drive Circuits; Volumetric Flow Rate Measurement - ABB MINI-MAG 10D1475 Series Instruction Manual

10D1475 MINI-MAG MAGNETIC FLOWMETER INSTRUCTION MANUAL
This may be expressed mathematically as:
(Equation #1)
E s =
where:
E = induced electrode voltage
s
B = magnetic field strength
D = meter pipe diameter
α = dimensionless constant
V = liquid velocity
Thus, the metered liquid constitutes a continuous series of conductive liquid disks moving through a
magnetic field. The more rapid the rate of liquid flow, the greater the instantaneous value of signal
voltage as monitored at the meter electrodes.

4.1.2 Magnet Coil Drive Circuits

In many conventional magnetic flowmeters the integral magnet coils are driven directly by the
customer's 50/60 Hz power service. The design of the Series 10D1475 magnetic flowmeter uses
magnet drive circuits which are alternately energized bi-directionally at a low frequency rate as
commanded by the associated Converter/Driver assembly.

4.1.3 Volumetric Flow Rate Measurement

The magnetic flowmeter is a volumetric flow rate measuring instrument. This can be shown by
substituting the physical equivalent of liquid velocity into equation #1 as follows:
(Equation #2)
V =
Substituting for V in equation #1
E s = 1 BD
and solving for Q:
∴ Q = παD
Since B = β E
r
and since α, D and β are constant:
(Equation #3)
Q = γ E
where:
Q = volumetric flow rate
A = cross-sectional area
D = pipe section diameter
E = induced signal voltage
s
E = reference voltage
r
B = magnetic flux density
α = dimensionless constant
β & γ = dimensional constant
V = liquid velocity
Therefore, volumetric flow rate is directly proportional to the induced signal voltage as measured by
the magnetic flowmeter.
4-2
1
BDV
α
Q = 4 Q
2
πD
A
4 Q
2
α πD
2
• E
s
4 B
s
E
r
FUNCTIONAL DESCRIPTION