MEGABRAS MPK-204 Manual De Uso página 12

4. Some notes about accuracy
In order to obtain the specified accuracy, the operator has to adjust the
test current to a value higher than the 80% of the nominal value. If it were
necessary, it is possible to use a lower current, but by doing this the
accuracy will be affected.
MPK-204 has an auto-compensation system that automatically eliminates
the error produced by internal offset. Thus, it is not necessary to carry out
measurements by reversing the polarity in order to compute the average
value. Nevertheless, if the operator suspect that there is a difference of
temperature between the contact points that would can generate
thermoelectric voltages, it is necessary to carry out two measurements by
reversing the current cables and so, the circulation sense of the current
through the resistance under measurement. The resistance value to be
measured will be the average between the values in one sense and in the
contrary (direct and inverse current).
The use of very long test cables in the 200 A range may prevent the
achievement of the nominal current. This will not harm the accuracy of the
measurement whenever at least 80% if the nominal current is achieved.
5. Protections
5.1. Start with I = O
Very quick variations of the current may cause damages to sensible
items. In order to avoid them, the equipment has a protection that
imposes to start the test with zero current. You can only start the
measurement if the current adjust control is at the start of its course. If
this were not the case, the Start would be inhibited and the message
would say START WITH I=O. If the operator sharply increases the test
current by quickly rotating the Test current control clockwise, the
equipment will impose a slow current growth, in order the current to softly
come to the selected value.
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