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Lake Shore Model 480 Fluxmeter User’s Manual
2-4 Magnetic Measurement Overview
2.1.6 Analog Versus Digital Integrators
Most of the integrator discussion in this manual is based on analog integrators. Analog integrators are
made with analog amplifiers, resistors and capacitors. Digital integrators approximate the action of
analog integrators by combining voltage sampling and software integration algorithms. There are
advantages and disadvantages to both types of integrators.
The performance of digital circuitry continues to improve and the price continues to decline. There are
now few analog functions that cannot be approximated digitally. Digital circuits are generally smaller
and have fewer discrete components. Their behavior is more repeatable with fewer calibrations.
Digital integration is likely the best choice to integrate predictable and well behaved signals.
Analog circuit technology is not standing still. Fast changing, high voltage, or very low voltage signals
are still integrated most accurately with analog integrators. The general purpose Model 480 uses an
analog integrator. The instrument must perform well with any type of input signal. The digital circuitry
surrounding the analog integrator offers most of the advantages of a fully digital circuit.
2.1.7 Fluxmeter Measurements In Magnetizers
Magnet materials such as Alnico and Samarium Cobalt are not permanent magnets until they are
conditioned in a magnetizer. The magnetizer produces strong fields by passing current through a coil
fixture. The magnetizer and coil fixture are optimized based on the magnet material and shape. If the
magnetizing field is not strong enough the magnet will not be fully magnetized.
Best cycle times and coil life are achieved when the magnetizer is operated at the minimum voltage
required to attain the needed magnetic field. The Model 480 provides an easy way to measure the
peak field when the magnetizer voltage is being determined during initial setup. Peak field is best
measured in an empty magnetizer fixture. During production magnetizing fixtures age and it is not
uncommon for a coil turn to short. Magnetizer current measurements are not enough to identify many
fixture problems. Peak field should be measured periodically as part of a quality control process and
to determine the general health of the fixture.
Many users want a way to determine if the Model 480 is fast enough to capture the peak field
generated by their magnetizer. The remainder of this section describes how the Model 480 can be
used with even the fastest magnetizers if the sense coil is designed properly. Discussion begins with
an approximation of the wave shape of the field generated by a magnetizer. The maximum rate of
change is then identified and it is shown how that rate of change is the only true limit on peak speed.
Finally coil sensitivity is discussed and examples are given of how to determine appropriate area
turns of a coil.
2.1.7.1 The Magnetizer Pulse
In many cases the magnetizer current is provided by a quick, high current discharge of a capacitor
bank. The shape of the magnetic field during this discharge is shown in the figure below.
P-Mag_pulse.bmp