Installation, Operation and Service Manual LKP Series
© 2020 DynAmp, LLC Page 23
041736 N
5. THEORY OF OPERATION
5.1 GENERAL
Figure 5.1 Magnetic Null Detector Diagram
A thorough knowledge of the LKP system theory of operation is essential for efficient
troubleshooting. In figure 5.1, a portion of the Measuring Head is shown to illustrate the
magnetic-null principle used in all Series LKP current measuring equipment.
5.2 MAGNETIC SENSOR (NULL DETECTOR)
The magnetic sensor produces a voltage output proportional to the difference between the
bus field and the feedback field. The sensor output is amplified and is returned to the
magnetic circuit in the form of feedback current. This current is passed through 5000 turns
to produce the feedback field.
The Measuring Head contains many magnetic sensors and feedback coils. Each set of
sensors and the adjacent coils plus the associated amplifying section of the Metering Unit
is termed a channel. Each channel responds nearly independently of the other channels to
null the bus field in its own section of magnetic core. However, after passing through their
respective coil groups, all channel currents are summed to produce the output current.
This current, which is always in the ratio of 1 A to 5000 A of bus current, is passed through
resistors or shunts to develop voltages for the meter and proportional outputs. The output
current itself is also available at the output terminals, which are jumpered if not used.
5.3 SYSTEM DESCRIPTIONS
Effects of stray fields are nullified by joining a number of magnetic assemblies like the one
just described in a closed path around the bus. Figure 5.2 shows four such assemblies
(referred to as a 4-channel assembly). A 4-channel system is used here as an illustration
to simplify the drawing and explanation.
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