Voltech AT360, User Manual

Page: 363 / 470

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ANUAL
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7-65
Choosing Test Limits
The limits may be entered as:
1. A nominal value together with a percentage tolerance (%)
Enter the nominal Primary to Secondary ratio, together with the
limits as positive and negative percentage values.
2. An absolute number of turns (#)
When limits are set as +/- an absolute number of turns, the tester
converts these limits to the % type in the following way:
= +/- (Pri Limit + Sec Limit ) x 100%
(Pri Turns Sec Turns )
(You can see the exact result of this conversion by clicking on %
limits in the Editor dialogue once the absolute, #, limits have bee
entered.)
For example, take a typical Switched Mode Power Supply
transformer with windings in the ratio of
200:10.
Typically, a prior measurement of inductance will have confirmed
the correct number of primary turns have been fitted with the correct
cores. Setting absolute limits of 0
on the primary and 1 on the
secondary
will result in limits of:
Nominal Ratio: 200/10 =20
Ratio + 1 sec turn =18.18
Ratio –1 sec turn = 22.22
Limits calculated by tester = (0/200 + 1/10) x 100%= +/- 10%
The equivalent ratio limits used by tester are:
Upper limit = 22. Lower Limit = 18