Endangering the Milliammeter

Radio Record, Volume VIII, Issue 25, 28 December 1934, Page 40

Endangering the Milliammeter

When nothing else happens to be available, there is a temptation to use a milliammeter in conjunction with a dry battery as an indicator of continuity. But such a procedure should: be strongly discouraged, both for the. beginner, who does not realise the possibility of damaging a comparatively expensive instrument, and for the more experienced enthusiast, who realises the danger but thinks he can aiequately guard against it. It will be fairly obvious that a milliammeter can only be used for this purpose when the circuit through which a test is to be made includes a high value of resistance-sufficiently high, in fact. to limit the current flowing to a value not exceeding the maximum rating of the instrument. But the danger is that in the process of testing a short-circuit may take place between the test leads. or, €ven more likely, they may be applied across a component which is thought to have a high internal resis(Continued at foot of next column.)

Senneterre tance, but where a short-circuit actual. ly exists. Unless one has a special instrument for continuity tests. the safe plan is to use a voltmgter in conjunction with a testing battery of a lower voltage than the maximum reading of the instrument, .