Installation, Operation and Service Manual
LKP Series
© 2016 DynAmp, LLC
Page 12
041738 I
5.4 MAGNETIC CONSIDERATIONS: MEASURING HEAD
Although the LKP systems are designed and built for accuracy, stability, and reliability,
these factors may be adversely affected by the arbitrary location of the Measuring Head
without regard for magnetic fields. Secondary magnetic fields emanating from other
sections of the bus being monitored or from other nearby buses may cause overheating.
Currents from other buses produce magnetic fields, which can sometimes cause zero
offsets and errors at low current levels. To guard against these problems, you can have a
computer analysis of your bus system made, or you can follow the guidelines presented in
this section.
FREE BUS ANALYSIS
The general guidelines below should be applied only when a detailed analysis of your
bus system is not available. DynAmp, LLC will perform one detailed computer analysis
of the proposed location of the Measuring Heads within your bus system at no charge.
Generally, this is done before or at the time the unit was ordered. In this way you are
assured that your system will function properly.
NOTE
: External magnetic fields do not affect the basic accuracy of the equipment,
provided channel voltage limits are not exceeded. The external field, however, will either
add to or subtract from the flux in the Measuring Head core pieces. If the external field is
too large, the dynamic range of the channel amplifiers may be exceeded. If the subtractive
vector is larger than the vector set up by the bus current being measured, the channel
current will go to zero and try to reverse. Since the LKP amplifiers can pass current in the
forward direction only, an error condition can exist. In the other case, where the vectors
are additive, the required current through a given set of coils may exceed the dynamic
range of the channel and result in enough heat to damage head components.
In most cases, it is possible to shift the position of the head relative to the bus to equalize
channel currents, so that the dynamic range of any channel is not exceeded and heat
distribution is more uniform around the head. Equalizing channel currents in this way will
prolong the life of the equipment. Measurement of channel voltages is the only way to
make sure that the individual channel amplifiers are operating within dynamic-range limits.
For further information, refer to the magnetic centering procedure in this section.
Whenever possible, the head should be installed on the longest straight run of the bus that
is available in an area free of other bus structures. General guidelines requiring
consideration when installing a Measuring Head are shown in Figure 5.2 (guidelines
illustrated are to be considered as the minimum required distances). If the proposed head
location can be physically described by more than one of the diagrams (Figure 5.2), a bus
analysis should be performed.
For the guidelines of Figure 5.2 to apply, the bus height-to-width ratio should equal the
head aperture height-to-width ratio, within ±10%. The ratio does not affect the accuracy of
the measurement, but it does affect the loading of different sections of the head.
