The sensitivity of modern arrow indicators is so high that at many of them current of a full deviation of an arrow does not exceed hundred microamperes. In practice quite often it is necessary to measure the currents estimated by hundreds milliampere and even amperes. The so-called shunt comes to the rescue.
1. Before starting production of the shunt, it is necessary to measure the internal resistance of the arrow indicator. For this purpose use an ordinary tester or a multimeter (not very well, arrow or digital). At the same time, it is necessary that current through the tested device was not too big, otherwise his shooter it can be deformed.
2. Now calculate tension which needs to be given on the indicator that his shooter deviated completely. For this purpose transfer current of full deviations in amperes, and the measured device resistance - to ohms. Then substitute them in a standard formula of the law of Ohm: U=IR where U is tension necessary for a full deviation of an arrow, I - current of a full deviation of an arrow, R - the measured indicator frame resistance. Be not surprised to the fact that tension calculated by this formula will turn out very small.
3. Now it is necessary to calculate resistance of the shunt. It will turn out so small in comparison with indicator frame resistance that the last can be neglected. Resistance of the shunt has to be such that when passing through it of the current which is for this resistance it is also possible to calculate by a standard formula of the law of Ohm, but transformed as follows: R=U/I where R is the required resistance of the shunt, U is the naprzheniye of a full deviation of an arrow of the indicator calculated by the previous formula, I - limit current on which measurement your ampermeter will be calculated (if it is expressed in milliamperes, previously transfer it to amperes).