ETS-Lindgren HI-1600 Microwave Oven Survey Meter - Manual (Page 7)

Introduction | 7
1.0 Introduction
The HI-1600's meter case houses a rugged meter, movement driven by an
operational amplifier and is powered by two 9 volt alkaline batteries. The
negative battery is used in conjunction with a stable voltage regulator that
provides the critical reference voltages required to maintain calibration of the
instrument. The circuit provides a stable integration circuit with a fast and slow
position switch. When used in the fast position the time required for the meter
needle to reach 90% of final value (with a constant cw microwave field input) is
less than one second. The slow position provides a longer time constant, just
under three seconds, allowed by the DHEW Performance Standard for
Microwave Ovens, CFR 1030.10. The meter is calibrated for measurements at
both 915 MHz and 2450 MHz.
The diode detection array of eight hot carrier diodes is housed in the large end of
the plastic probe. This antenna array has the unique feature of being able to sum
microwave electric fields at any polarization in a plane perpendicular to the axis
of the probe. The antenna lobe is also very broad, making the instrument easy to
use when measuring leakage around an oven door. The spacer is designed to
provide five centimeter spacing (as required by the HEW standard) from the
outer surface of the probe cover to the center of the array. The shape of the
probe provides minimum perturbation of the fields impinging on the diode array.
This instrument is calibrated with the hemispherical cover in place, testing
without the cover may cause erroneous readings. The probe is attached
permanently to the meter case by 48 inch (1.2m) shielded cable. Each detection
probe and meter amplifier is calibrated as a unit. Two ranges, 0-10 and 0-20
mw/cm 2 , are provided at 915 MHz and one range, 0-10 mw/cm 2 , at 2450 MHz.
The instrument is calibrated at an ambient temperature of 75° F (23º C) and will
give reliable readings under most temperature ranges. Care should be taken,
however, when using the instrument after it has been stored in extreme cold or
hot conditions. The inability to zero the meter, or a zero that is drifting rapidly,
prior to taking a reading usually notes this condition. If this condition is noted,
allow 15 minutes for the meter to reach room temperature prior to recording
readings.