To measure a large DC current, such as tens of AMPS, and even greater, hundreds of AMPS, there is no such a large range of current meter for the measurement of current, how to do? It is necessary to use shunt. Is a short piece of conductor, can be all kinds of metal or alloy, connecting terminal; the DC resistance is strictly a good tune; connected in series in the DC circuit, the DC current excessive flow device, both ends of the shunt produced DC millivolt voltage signals, and then in the measurement of the shunt at both ends of the table pointer swing, the reading is the current in a DC circuit values. The so-called triage, a small current to drive indicator, in the small current (MA) and loop current (1a dozens of a) the proportion of smaller, the current table indicating readings of linear better and more accurate. This is the electric circuit of the common products, lightning protection and diversion measures.
The current meter has a variety of different specifications, but the actual meter is standard millivolt meter. For example, a full scale voltage meter for 75mv. So with this voltage meter measurement such as 20A current, you need to give it a 75mV voltage drop of the shunt resistance in the current flowing through the 20A when, also known as 75mV shunt.
Shunt is a to the resistance of the current through the general common 15a and 20a and 35A current meter are the need for a shunt, shunt impedance = header logo full voltage / header full scale current. Such as 20a of the ammeter shunt resistance =75mv/20A=0.00375 Omega, constant impedance according to Ohm’s law U=IR, voltage and current into a proportional, current is linear voltage is linear, so we can use a full 75mV to the voltage of the table shows the current. Therefore, the use of the current meter is actually a voltage meter.
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