PROGRAMMING TESTS VOLTECH AT3600 USER MANUAL
PAGE 3.4.20. VPN 98 - 024 TEST PROGRAM EDITOR
Choosing the test limits
The limits may be entered as :
1. A nominal value together 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
Which equates to the actual ratios with a one turn error on the secondary.
In general, the voltages obtained during any voltage turns ratio test will not equate
exactly to the theoretical calculation of Np / Ns, because, for example, of the relative
positions of the windings with respect to each other and the core.
General Rule
When setting turns ratio limits in absolute terms, use a limit of ½ turn less than the
number of turns you want to detect. In this case set a limit of 0 (pri) and ½ (sec). This
will result in equivalent limits of 19 and 21. Ideal for detecting an errors of 1 turn or
more.
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