Siemens Milltronics Millpulse 600, Instruction Manual

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Page 8 Milltronics MillPulse 600 – INSTRUCTION MANUAL 7ML19985DG02
Operation
Milltronics Millpulse 600 works on the principle of Faraday’s Laws of Electromagnetic
Induction. When a ferromagnetic object (target) enters the probe’s permanent magnetic
field, it distorts the flux causing it to cut the coil windings, thereby generating a voltage.
This voltage is proportional to the speed at which the ferrous target passes through the
flux and is inversely proportional to the square of the distance between the target and
the probe.
Square profile targets work better than round because they present a sharper transition
in ferrous mass. Minimizing the gap is more effective than an increase in target size
beyond 5 cm x 5 cm x 2.5 cm (2” x 2” x 1”), except at very low velocities.
The voltage generated from the probe coil is fed to a processing circuit. The processing
circuit controls a semiconductor switch that opens and closes in response to the
incoming pulses. The switch is normally open (LED off) and closes when a pulse is
generated (LED on). The switch duration times are held to a minimum of 50 msec to give
the PLC sufficient time to read the switch states.
The amplifier has been tuned for a response typical to the range of speed encountered in
industrial applications. This response governs the relationship between target speed and
probe to target gap, as demonstrated in the following chart. The resultant curves indicate
the maximum velocity is about 33 cm/sec. (65 ft/min), and with a velocity of 1 cm/sec.
(2 ft/min), a maximum gap of 3.1 cm (1.25”) is possible.
This graph was plotted from tests using four ferrous blocks set equidistant on a 41 cm
(16”) diameter circle on a non-ferrous disc.
‘A’
2"x1"x2"
ferrous target
‘C’
2"x1"x1"
ferrous target
‘B’
2"x2"x1"
ferrous target