Current Monitor 20 - 50 Amps

gevv · Tarih: 15.12.2006, 15:14 Mesaj konusu: **Current Monitor 20 - 50 Amps**

Measuring high currents at low voltages has always been a problem. The classic way to measure current is to measure the voltage drop across a series resistor – easy in the vacuum-tube era when we had lots of voltage and low current, but transistor circuits won’t tolerate much voltage drop without affecting circuit operation. An ammeter just combines the resistor and voltmeter – I’ve used one for years, but it doesn’t have very good accuracy or resolution. The choice of resistor is a problem: while a large resistance produces too much voltage drop, a very small resistor produces a small voltage drop, so getting good resolution is difficult. To get decent resolution, we must accept some loss. Another problem is that it is difficult to measure a small voltage difference between two large voltages; for example, if we are measuring a 50 millivolt drop from a 12 volt battery, we might be trying to accurately measure the difference between 12.8 volts and 12.75 volts. Some commercial “power analyzers” avoid this problem by putting the resistor in the negative lead. This works fine if there is no other path for current, but care is required. Suppose we wanted to measure the current drawn by a mobile transceiver; if we simply inserted the power analyzer in the power wires, the voltage drop in the negative wire would cause some of the current to flow through the coax braid and back to the car frame. The stray current would not show up in the measurement,

expres pcb
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