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6.5 Target Scaling
The preferred method for determining a target scaling factor is to use the Auto
Scaling feature of the 440 System described in section 6.3.1.1 "Target Scaling" on
page 6-10.
You should perform the following procedure whenever dry-land testing is neces-
sary on a specific target. This might be, for example, when the target does not fall
easily into one of the four standard categories.
For most applications, it will be sufficient to determine the target scaling factor only. However, if you
must define the complete performance envelope of the System for a specific target, you may need to
extend the procedure to include a full assessment of the vertical range accuracy, based upon a large
number of measurements.
6.5.1 Target Scaling Procedure
System configuration
Establish the 440 System on dry land so that, while keeping the coil array level, you may move it easily
to various heights above the sample target. A suitable arrangement could include two adjustable
vertical props holding a wooden support frame on which you mount the coils.
The sample of target must be no shorter than 5 metres.
Power-on the 440 System and allow a period of 15 to 20 minutes for the System to stabilise. Then, with
the target removed from the immediate test area, perform a background compensation with the coils
supported 1 metre above ground level.
Position the coil array so that, when you move it through a range of heights, the background level does
not change by more than 5µV – use the Run Display screen to observe the signals from the three
channels.
Estimate the Target Scaling factor
Use the Auto-scaling feature and choose a target type, diameter, and weight-coating that matches the
specific target as closely as possible. Record the values on Form D1 in
Procedure" on page
D-3.
Make a note of the value suggested by the 440 System for the target scaling factor and use this as the
first estimate in the scaling process.
Determining the nominal Target Scaling factor
Position the target under the centre of the search-coils, and ensure that the target and the coil array
are mutually at right angles.
Using the first estimate of the target scaling factor, record the true vertical range to target against that
shown on the Run Display screen of the 440 System for a number of different vertical ranges. Also,
record the signal strengths measured by each of the search-coils.
Use Form D2 in
section D.2 "Target Scaling Results" on page D-5
DPN 402196 Issue 4.1
NOTE
Chapter 8 "System Specifications"
© Teledyne TSS
6 – Operating Procedure
includes some typical charts of this type.
section D.1 "Target Scaling
to record the test results.
6- 33
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