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DC Gaussmeter Model DG-800
Instructions
This magnetometer (gaussmeter) measures DC magnetic field (with polarity) up to + or - 799.99 gauss.
Operation:
Turn the meter on by pressing “Power” for at least 1 second. Note that the last few millimeters at the (black) end of the
probe has a square bulge on one side; the other side is flat. Note also that a small section of brass is visible about 15mm
from the t
ip. The brass is on the “flat” side. The center of that square bulge is the location of the Hall-Effect sensor, which
is very small (0.2 x 0.2 mm). Place the flat side of the probe’s end (not the square bulge side) against the surface to be
measured. A negative sign indicates that the probe is touching the south pole of a magnetized object; in contrast, a north
pole will read positive (“positive” is indicated by the
absence
of a polarity sign on the display). The actual center of the
sensor is 1.1mm above the flat surface or 1.0mm below the top of the square bulge) and is centered in the center of the
square bulge.
Below 10 gauss, only three digits (such as “-0.37”) will be displayed. For stronger fields, more digits will appear. For fields
stronger than +/-
799.99 gauss, the extreme left digit will display. (It is a “1”). If the display reads “LO BATT”, there is
about one hour of battery life remaining. Remove the soft bumper or “boot” if present, and then slide off the battery door
on the back side. Replace with a common 9-volt rectangular battery. Alkaline is preferred. The old battery can most easily
be removed by holding the meter so that the battery can fall out, and then tapping the meter on a table. Current drain is
7ma and the LO BATT reads if battery voltage remains below 7V for at least one minute. (Accuracy errors will occur below
battery voltage of 5.8V). You may need to press “Power” twice the first time with a new battery.
METER TURNS ON AFTER REPLACING THE BATTERY.
MAKE SURE THE
Offset Adjustment (only necessary if measuring weak fields):
The offset controls allow you to add or subtract any field to or from the displayed number of gauss. This feature is used if
you are holding the sensor in a certain orientation in space, and you want the display to show “zero”, even though some
field is pr
esent. Press “Auto Zero” to do this. Then you can bring in a magnetized object to measure. This is the magnetic
equivalent of adjusting the “tare” weight of a weight scale, because there may be an ambient magnetic field that you’ll
want to subtract out. When turned on, the display will read approximately zero in zero field, but you can more precisely
adjust the offset to zero if you do one of two things, either:
1) Place the sensor in a
“zero gauss chamber” (not supplied with this meter) and then press Auto Zero.
2) Place the sensor end flat on a non-magnetic table or desk with the square bulge facing up. In this orientation, the meter
will read the upward-pointing component of the magnetic field. (If the field is instead
downward
-pointing there, the meter
should then read a negative number.) Note the number on the display. Then flip the sensor so the square bulge is facing
down. This 2
nd
reading should be the
negative
of the 1
st
reading. That is, if the 1
st
reading was
–0.40 (gauss), then the 2
nd
should be 0.40 (gauss). If the two readings are not the negative of each other, then the offset is not adjusted perfectly for
a zero reading in zero field. For example, if the 1
st
reading is 1.00, and the 2
nd
reading is 0.00, then the offset is off by 0.50
gauss (the average of the two readings). Adjust the offset knob so that the 1
st
and 2
nd
readings re the same number but
of opposite sign. Offset is adjusted by pressing
the “+” or “-” buttons. If you hold one button down, the offset amount will
