SKF AWAIV-12, User Manual

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operational characteristics that can be enhanced or fine tuned to meet specific additional
requirements. Hi L technique is an example of this.
In essence, the useful range of electric coils that can be tested by the Baker AWA-IV is
dictated by the capacitance (C) supplied by the test set, and the inductance (L) of the coil
under test. The “Q” factor—or loss of the test object—also has a direct influence.
Per the data specifications, the Baker AWA-IV 2 kV and Baker AWA-IV 4 kV models are
supplied with a .1 microfarad energy storage capacitor. To illustrate the phenomena at work,
this value (0.1) shall be the basis of the following discussion:
The sample, or data acquisition window of the Baker AWA-IV 2 kV and Baker AWA-IV 4 kV
models are dictated by an analog to digital converter, and the memory size assigned to it.
Without going into detail about these signals, or memory depth, suffice it to say that the
maximum sample time of both models is approximately 2 milliseconds.
This illustrates the transient nature of the surge pulse. It is applied, measured, analyzed, and
displayed in a fraction of a second.
The Baker AWA-IV 2 kV analyzer has a capacitor with a value of 0.1 micro-farad. The
frequency (f) generated—and therefore, the sample width needed—when a 100 micro-
henry coil is tested with the standard surge test is calculated using the following formula:
LC
f
π
2
1
=
becomes
6 6 1 . 100 2
1
− − ∗
=
π
f
when solved,
reveals a ringing or resonance frequency of approximately 50 kHz. The period of said 50 kHz
sinusoid is equivalent to
f
1
or approximately 0.00002 second. This is well within the sample window width detailed
previously.
What happens to these frequencies if the inductance of the tested coil is raised by several
orders of magnitude? For example, what if the coil inductance is now 5 henry, or 50,000
times greater?
6 1 . 5 2
1
− ∗
=
π
f
when solved, reveals a frequency of approximately 225 hZ
The period of this signal is
f
1
or approximately .0044 seconds.
This is more than double the capability of the data acquisition sample width hardware to
capture it! Therefore, the question becomes: how do we capture such a signal and display it
appropriately across several orders of magnitude?
The answer is to employ the Hi L technique. The Hi L technique, in practical terms, functions
as a test range extender. In other words, it allows the Baker AWAIV-2,-4 to deliver sensitive
SKF Static Motor Analyzer—Baker AWA-IV User Manual 103
Special features of the Baker AWA-IV