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30.3.2 Test circuit gain calibration. Gain calibration of
the filter can be accomplished by use of the circuit show in
Figure 7 (Note: To use this circuit, the excitation circuit and 14
turn magnetometer must be disconnected from the test circuit at
TP1) .  The test signal of the circuit in Figure 7 closely
approximates the flyback voltage and input signal normally seen at
TP1.  The test signal, as measured at TP1, shall be a 1 kilohertz,
4 volt, negative ramp with 10 hertz, 20 millivolt peak to peak
modulation.  For the circuit in Figure 6, the normal gain of the
biquad filter is 250.  R27 is adjusted so that the overall gain at
TP4 is 250.  That is, the output at TP4 is a 10 Hz ac signal whose
peak value is 250 times the peak value of the 10 Hz ac input
signal at TP3.
30.4 Magnetic environment.  The magnetic environment for the
core test must be resistant to externally time varying and random
magnetic signals.  The probe fixture is to be located at a depth
equivalent to one diameter of a suitable magnetic shield. A
typical implementation is shown in Figure 8.  The DC bias test
fields, and the 10 Hz ac drive signal field must be generated by
coils within the magnetically shielded volume.  All magnetic
calibration measurements shall be made at the probe head for both
the bias and drive signal calibration.
Methods of inspection.
40.1 Test geometry.  Core orientation in the test fixture
shall be as follows.  The dot, which signifies the location of the
weld mark, shall lie in the plane of the magnetometer coils and be
placed as far away from the interconnect assembly as possible, as
shown in Figure 9. This is to reduce the influence of the magnetic
discontinuity of the weld mark.  The plane of the probe head test
coils shall be perpendicular to the axis of the bias and drive
coils, but offset to allow the core to be at the coil's axis to
reduce magnetic field strength gradients.
40.2 Core sensitivity.  Core sensitivity shall be measured
using the test circuit described and calibrated herein.  The
magnetometer shall be oriented as shown in Figure 9.  Output at
TP4 shall meet the requirements of 3.3.1 with Z = O.  The waveform
across the 14 turns (TP1 of Figure 1 and Figure 2) should be as in
Figure 5.  The waveform shall reach zero volts before 30
microseconds to ensure core saturation.
40.2.2 Core linearity.  Core linearity shall meet the
requirements of 3.3.2 using the test described in 40.2 except Z =
+0.45, and Z = -0.45 oersteds.

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