AlphaLab VGM Instructions

Vector Magnitude Gaussmeter Model VGM Instructions
Quick Start: Turn the left knob to "Measure". The magnitude of the magnetic field (at the tip of the aluminum sensor)
will be displayed. The values of the X, Y, and Z components can also be displayed by pressing "View". If the knob is
turned to "Peak Hold", similar parameters are displayed, except that they are the peak values for magnitude X, Y and
Z. Depending on how the meter has been adjusted, there may be offsets present (similar to the "tare" on a weight
scale). These can be adjusted by the "Reset" button on the "OFFSET" knob, to be explained below.
Power: As shipped, a standard 9 volt battery is installed. Battery life is about 10 hours (25 ma drain; 6.5 volt
dropout). "Low battery" appears when about one hour of battery life remains. Pull off the rubber boot if present (the
soft bumper around the meter) and slide off the back door to replace. It is easiest to remove the battery by tapping
the meter (against a table) on the back side of the meter near the battery door. The AC adapter can be substituted
for the battery. When plugged in (left edge of enclosure), the adapter disconnects the battery (does not charge the
battery). If the meter is on when changing from battery to adapter, it may turn off. To restart it, see "system reset"
below.
System reset (if meter does not turn on): To restart the meter (and return to the factory-preset offsets for X,Y,Z), turn
the meter to "Measure" and plug the AC adapter cord without the AC adapter being connected to power. Then turn
the meter off and disconnect the cord from the meter. System reset can also be done by removing the battery while
the meter is on, then turning the meter off and replacing the battery. The system resets because power is interrupted.
This includes interruption of internal capacitor power, which has enough energy for 30 seconds while the meter is off,
or 0.01 sec while it is on.
Simple measurements: Turn the left knob to "Measure". Notice "DC" on the display and a triangle under the word
"Magnitude". The number shown is the DC magnetic field, in gauss, and is sensed at the tip of the probe. It is the
field magnitude, meaning the square root of the sum of the squares of the X, Y, and Z field components. If the probe
is not near magnetized objects, it will read the Earth field, which is typically about 0.50 gauss. You can begin
measuring the field immediately, although when first turned on, a transient offset in the reading of as much as 0.20
gauss may occur. This offset disappears within 5 seconds, which is the full warm-up time. If you need to read fields
of less than few gauss, wait at least 5 seconds after turning on.
Besides the magnitude, the separate X,Y,Z values (the vector components of the field) can be displayed by pressing
"View". When pressed once, the displayed triangle will be under "X Axis", and only the X component of the field will
be shown. Pressing again goes to Y; again goes to Z, and pressing one more time returns to "Magnitude" Unlike
magnitude, each one of these XYZ components can be negative (as well as positive), and the range of each of X,Y,Z
is -799.99 to +799.99 gauss. (The range of the "Magnitude" is 0.00 to 799.99 gauss. Stronger fields will not harm the
meter or probe, but the display will indicate over-range at 800 gauss and above, which will appear as " 1- - - . - -").
The easiest way to measure the field on a surface (of a part) is by sliding the probe along the surface. The probe can
touch the surface either on the probe's aluminum side or on its black top face. The image below shows the location
of each of the X,Y,Z sensors. Each sensor is small (< 0.2 x 0.2 x 0.1 mm) so that each measures essentially one
point in space. The image shows orientation relative to the small black triangle, where one of the four top corners of
the probe has been notched and painted black. When trying to measure exactly at the surface of a part (or as close
as possible to the surface), orient the probe so that the Z face (top face) is touching the surface. (The Z sensor is
only 0.6 mm beneath the top face of the probe, whereas X and Y are 0.9 deep beneath the aluminum surface.)
Select "Magnitude" for checking residual magnetization.
1