Zero resistance ammeter

Ranked #95 on the list Best Measuring Instrument of All Time

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About Zero resistance ammeter

  • Dimension measured: Electric current
  • Subclasses:
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A zero resistance ammeter or "ZRA" is an instrument measuring the electric current (practically) without voltage drop across the ammeter. A standard current meter, as usually built-in in typical multimeters measures the current as a voltage drop across a shunt resistor. A usual digital 3½ digit voltmeter has a lowest current range of 200 mV, accordingly rises the voltage drop across the internal shunt resistor up to 200 mV when the current corresponds to the full range. Example: You measure a current of 100 µA in the range 200 µA of the digital voltmeter. Typically, the internal shunt resistance in this range is 1 kΩ, across which a voltage of U = R x I = 1000 Ω x 100 µA = 100 mV will drop. When measuring the current in usual electronic circuits, this voltage drop may be disregarded. For electrochemical cells, a drop of 100 mV is nearly enormous. Electrochemists therefore need zero resistance ammeters to measure the current without producing a voltage drop. To achieve this, special zero resistance ammeters, also called "active current sinks", are used. Potentiostats e.g. can be used also as ZRA, and it is very simple to do so. Connect the counter electrode terminal to the

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