Pre-Amplifier (Ima And Rma); Mfa 4P Operation - Siemens milltronics MFA 4P Instruction Manual

The resultant line indicates the threshold tolerance of the accompanying MFA 4p
electronics. For example, in FIG. A, a 100 mm (4") gap requires a minimum velocity of
about 10 m / minute (35 ft / minute): with a velocity of 0.61 m / minute (2 ft / minute), a
maximum gap of 31 mm (1.25") is possible.
25.4 mm = 1 inch and 0.305 m = 1 foot
Note:
The graph was plotted from tests using four ferrous blocks set equidistantly on a
406 mm (16") diameter circle on a non-ferrous disc.
The physical shape of the ferrous target generally becomes important at low velocities or
large gaps. At these points, tests indicate that a cubic shape gives the best results due to
the sudden change it causes in the magnetic field.
An increase in block size beyond 50 x 50 x 25 mm (2" X 2" X 1") is generally not as effective
as minimizing the gap, except at very low velocities.
The Milltronics Mini Sensing Probe, MSP-1
• The MSP-1 is approximately one-quarter the size of the standard probe with about
one-eighth the sensitivity.
• Divide all operating values by 0. 1 25 to obtain the specifications of the MSP-1.
For example, with a gap of 12 mm (0.5"), the minimum velocity is approximately
60 m / min. (200 ft / min.), and with a velocity of 0.6 m / min. (2 ft / min. )
a maximum gap of 0.125" (3 mm) is possible.
Milltronics manufactures probes to suit a wide variety of environments: low temperature,
high temperature, corrosive, and Class I, II and III applications.

Pre-Amplifier (IMA and RMA)

The pre-amplifier accepts the voltage pulses generated by the probe and converts them
into noise-immune current pulses. Current levels are 12 mA low and 45 mA high. The pre-
amplifier comes internally mounted in the probe, or in an enclosure for remote mounting.
Internally mounted pre-amplifiers are called IMAs. Remote mounted pre-amplifiers are
called RMAs.

MFA 4p Operation

The MFA 4p provides a short circuit protected, +24 V DC unregulated supply to the pre-
amp. In the event that the interconnecting wiring is shorted, output current from the
MFA 4p is automatically limited and the on-board alarm relays are de-energized to
indicate failure.
The output current pulses from the pre-amp are super-imposed onto the dc current
supply. These are monitored by Probe LED 1, which is illuminated at the rate of the
incoming pulses and is useful for positioning the probe.
The rate at which the pulses are received by the MFA 4p is compared to a setpoint
reference signal from the time base generator.
7ML19985FM01 MFA 4p - INSTRUCTION MANUAL Page 13