Operating Principles; Mfa 4P; Probe - Siemens milltronics MFA 4P Instruction Manual

Operating Principles

MFA 4p

Milltronics MFA 4p is a highly sensitive, single setpoint motion sensor alarm unit, used
with MSP and XPP probes. The probe detects an increase or decrease in the speed of
rotating, reciprocating, or conveying equipment and sends the information to the MFA 4p.
The MFA 4p works with a pre-amplifier which can be internal to the motion sensing
probe, or remote from the motion sensing probe.
Pulses generated from the probe are continually compared to the adjustable setpoint. If
the pulse rate is lower than the setpoint, the alarm relays operating in a faiI-safe mode
will de-energize, indicating failure. The relays will not energize until the pulse rate
increases above the setpoint.

Probe

The Milltronics probes work on the principle of Faraday's Laws of Electromagnetic
Induction. When a ferromagnetic object enters the probe's permanent magnetic field, it
distorts the flux causing it to cut the coil windings and generate a voltage. This voltage is
proportional to the strength of the magnet and the number of wire turns in the coil
(constant in the Milltronics probes) and the speed at which the ferrous target passes
through the flux. The generated voltage is also inversely proportional to the square of the
distance between the target and the probe.
The relationship between speed and gap of a standard probe:
Page 12
(25.4 mm = 1 inch and 305 mm = 1 foot)
FIG. A.
50 x 25 x 50 mm
(2"x 1"x 2")
ferrous block
MFA 4p – INSTRUCTION MANUAL
FIG. B
50 x 50 x 25 mm
(2"x 2"x 1")
ferrous block
FIG C
50 x 25 x 25 mm
(2"x 1"x 1")
ferrous block
7ML19985FM01