ETS-Lindgren HI-3627 ELF Magnetic Field Meter - Manual (Page 16)

Page -- 8 HI-3627 Manual
The connection for the recorder output is made through the
same connector as the battery charger (refer to figure 3-2). This
is a two circuit connector (jack) that mates with a standard ¼
inch stereo phone plug. The ring of the phone plug is reserved
for battery charger input and the tip is connected to the recorder
output. The shaft of the plug is the common ground. A diode in
the battery charging circuit keeps the battery voltage from being
applied to the recorder output when a plug is inserted into the
jack.
The recorder output comes directly from the circuit driving the
meter movement. The maximum current available to the
recorder output jack is 1 milliampere (5000 ohm minimum
recorder output load). A lower impedance recorder output load
will affect the accuracy of both the meter reading and the signal
to the recorder output.
The meter movement and the recorder output are driven by a
PWM (pulse width modulator). This leads to a small amount of
ripple on the recorder output, typically 50 mV at 40 Hz.
Low Battery Indication
The HI-3627 Magnetic Field Meter includes a "Low Battery"
indicator. This is an LED mounted on the front panel (refer to
figure 3-1). It is normal for the LED indicator to briefly blink
when turning the switch to various ranges and when turning the
instrument off.
If the "Low Battery" indicator remains on during operation, the
battery must be recharged. When the "Low Battery" LED lights,
about 10 minutes of useful operation remains. This relatively
short time is due to the output voltage of a NiCad battery
remaining relatively flat until the battery is almost completely
discharged, and then dropping very rapidly.