DESCRIPTION
Test Method RS101 of MIL-STD-461D requires
radiated magnetic fields over the frequency range
30 Hz to 100 KHz to determine the susceptibility
or immunity of the equipment under test (EUT).
Two loop antennas are required for compliance
with the requirements.The radiating loop is 12 cm
in diameter and the sensing loop (used for
calibration) is 4 cm in diameter. The Type 9230-1
Radiating Loop has been designed so that the
Type 9229-1 Loop Sensor can be attached at
the required 5 cm distance.
APPLICATION
The test method requires calibration of the
radiated energy at 1.0 KHz prior to the test.
Calibration of the Type 9230-1 Radiating
Loop is accomplished by coupling the Type
9229-1 Loop Sensor to it at a distance of 5 cm.
The arrangement is indicated in Fig. 1 on the next
page.With a known current flowing in the radiat-
ing loop, the magnetic field can be measured.
Two graphs are supplied with the loops to make
life easier for the test engineer. Fig. 2 shows
a typical correction factor curve for the Type
9229-1 Loop Sensor.Fig. 3 indicates the amount
of current flowing through the Type 9230-1
Radiating Loop to generate the required
magnetic field, in dB/pT.
The current level to produce 110 dB/pT at
1.0 KHz is 3.0 mA. An accurately calibrated EMI
meter or spectrum analyzer will measure this
as 42 dB/µV. Adding the correction factor of
68 dB/pT/µV from Fig. 2 equals 110 dB/pT as
required by the specification.
In those instances where the spectrum analyzer
does not have sufficient sensitivity, the calibration
can be accomplished just as well at a higher
current level. For example, using 300 mA, the
measurement would be 82 dB. Subtracting 40 dB
from this answer and adding the 68 dB factor will
equal 110 dB/pT/µV.
Another approach to the calibration and the
measurement depends on the accuracy of the
EMI receiver. Simply subtract the sensor correc-
tion factor in dB/pT/µV (Fig. 2) from the desired
magnetic field level in dB/pT (Fig. 3). Then adjust
the current until the EMI meter reads this value
in dB above one microvolt.
Example: For a field of 110 dB/pT at 1.0 KHz,
subtract 68 dB (Fig. 2) from this to obtain 42 dB.
This value in dB above one microvolt on the EMI
meter is equal to 126 µV as indicated in RS101.
A typical calibration test setup is shown in Fig. 4a.
For current levels below 25 mA, it is feasible to
use a standard laboratory signal generator. For
higher current levels, the signal must be amplified
(Fig. 4b). Both methods show a 0.1 ohm precision
resistor (Type 9817-0.1) and a digital voltmeter
for measuring the current.
USEFUL ANCILLARY DEVICE
Type Type 9817-0.1 Precision Resistor, 0.1 ohm,
1%. For measuring current flowing in the
radiating loop.
TYPE 9230-1 RADIATING LOOP; TYPE 9229-1 LOOP SENSOR
for MIL-STD-461D/RS101 magnetic field tests
45
(1 pages)
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