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magnitude drops below the alarm level) for the sound to stop. An alarm output jack is on the left side of the meter.
During the time that the alarm is sounding, the center pin of the jack will be at +3 volts; at all other times, the output
is zero. This feature can be used for automated pass/fail verification.
Typically the alarm can be set at about 10.00 gauss. Then a part can be rapidly scanned. By listening for the alarm,
the area of strongest magnetization can be quickly found; it is usually in the center of the zone in which the alarm
sounds.
Peak hold:
Whenever the meter is on (whether the left knob is set on either “Measure” or “Peak Hold”), the internal
memory stores and continually updates four peak hold numbers. Every 5 milliseconds, the present values of
magnitude, X, Y, and Z are compared to the four numbers in memory. If the present value of any of the variables is
higher
than the corresponding number in memory, then that memory is replaced by the higher number. This
comparison occurs 50 times faster than the display update, so that peaks can be detected that are too fast to be
displayed. For example, suppose the peak hold number stored for the Y axis is 322.74 gauss. Then for 7
milliseconds the Y field peaks at -455.37 gauss (or its average over a 5 ms time is that value). The Y peak hold
memory will immediately be changed to -455.37 (note the change to a negative value because the actual peak field
was negative in this example). The Y peak will stay at that new value until either a higher peak in Y occurs or “Reset”
is pressed while peak hold is being displayed (i.e., when the left knob is set to “Peak Hold”).
Notes about Peak Hold:
When peak hold is being displayed, the “View” button still toggles between the four
variables (but the peak value of each is displayed, and these numbers will stay constant most of the time). Also the
alarm still operates, and the peak comparison every 5 ms continues. In this mode, pressing “Reset” will return all four
peak hold numbers in memory to the
present
values of magnitude, X, Y, and Z, and the peak comparison process
begins again. The peak of the magnitude can only be a positive number, but X, Y, and Z peaks can be negative,
depending on the polarity of the peak
absolute value
of the vector field component. If a single event causes X,Y,Z to
peak simultaneously, then the displayed peak hold magnitude will exactly equal the square root of the sum of the
squares of the peak values of X, Y, and Z. However, all four variables may instead have peaked at different times. If
this happens, then the peak hold magnitude will be
less than
the square root of the sum of the squares of the peak
values of X, Y, and Z.
In general, all functions that operate while the left knob is set on “Measure” will also operate in the same way on
“Peak Hold”. Instead of displaying the actual values of magnitude, X, Y, and Z, the display on “Peak Hold” will show
the highest value of these variables. These numbers remain constant most of the time; they only change when the
probe is exposed to a stronger field than the previous maximum. Then they may change to a new, higher number
and stay that way until there is an even stronger field.
Offsets:
For most types of measurement, whenever the probe is in zero field, all four variables (on “Measure”)
should also display as zero. As shipped, each of X,Y,Z reads 0 +/- 0.10 gauss when the probe is in a zero gauss
environment. You can manually improve the offset zero error (of +/- 0.10 gauss) by placing the probe in a zero gauss
chamber (an optional accessory for this meter) and then press “Reset” while magnitude is displayed on “Measure”.
This will change the zero (tare) of X,Y,Z so they all read zero in that field. This new “tare” or offset will be
remembered even after the meter is turned off and back on. The factory preset offset can be restored either by doing
a
“System reset”
, as described near the top of these instructions or by pressing
downward
on the OFFSET knob
and releasing it so that a triangle appears over the phrase “Offset Adjust”, and then pressing the “Reset” button.
Press downward on the OFFSET knob one more time to eliminate the triangle. You can skip the remainder of this
“offset” section unless you need to measure very small field variations (less than 0.10 gauss).
Fine-tuning the offset without using a zero gauss chamber:
This is slower than with a zero gauss chamber, and
requires about two minutes. Remember that jitter in the reading is about +/- 0.02 gauss, so it is difficult to do these
adjustments perfectly. To adjust the offset, first find a horizontal nonmagnetic surface that is at least 30 cm (12”) from
any magnetized objects. (You can use the meter to determine if anything is magnetized nearby.) A wood or plastic
table works well at any location away from its steel supports, if it has any. Set the knob to “Measure” and press
“View” so that X is displayed. In the image above (near the beginning of these instructions), note the location shown
