Teledyne 440, Системное руководство, Страница: 114 / 256

6 – Operating Procedure
6-10 © Teledyne TSS DPN 402196 Issue 4.1
6.3.1 Establishing the Survey Configuration
6.3.1.1 Target Scaling
Target scaling is the method used by the 440 System to determine the relationship between the coil
signal strength and the range to the target. It allows the System to know whether a specific signal level
comes from a small target close to the coils or a larger one farther away.
The value you use for the target scaling factor depends upon the nature of the target itself – particularly
its diameter and its physical characteristics. You may establish this using one of two methods that you
may access by ‘System parameters’ Menu:
1. Auto Scaling
2. Entry of a known value for the Target Scaling factor.
Use of the correct value will allow accurate measurements on the target. However, due to the influence
of a sixth-root term in the calculation, absolute accuracy is not necessary when you enter a target
scaling factor. Trials have shown that, when using a target scaling factor that is 100% too high, errors in
the measured range to target will not exceed 20%.
Auto Scaling
This is the preferred method for setting a target scaling factor. It uses the stored database of target
characteristics to determine a suitable value for the target scaling factor for use in the range calculation
formula.
Before the System can determine the correct Target Scaling factor, you must supply the following
information about the target:
Upon completion, press OK to determine the correct value for target scaling factor. The SDC will
display this value and allow you to accept or reject it. Press [OK] to use the displayed value.
This completes the Auto Scaling process.
Known Target Scaling factor
This menu option allows you to enter a target scaling factor that you have determined by performing a
separate series of tests for a specific or unusual target.
The target scaling value is designed to be as close as possible to that used for the previous 340
system. However, for maximum accuracy it is recommended Teledyne TSS determine an exact target
scaling factor from a sample of your target.
See section 6.5 "Target Scaling" on page 6-33 for the full procedure to measure the scaling factor of a
target.
6.3.1.2 Threshold
High settings will make the 440 System less sensitive to noise but will also decrease its operating
range. The default setting of 25µV has proved to be suitable for the majority of survey operations.
Target Diameter Enter the external diameter of the conductive part of the target.
Note: If you select Flexible Pipeline as the target type, you must set the internal diame-
ter.
Weight Coating /
Jacket Thickness Enter a value between zero and 20cm for the thickness of any non-conductive coating
on the target.