Voltameter

A voltameter is a historic instrument for measuring the electric charge ( quantity of electricity ). An alternative name is coulometer or Coulombmeter. It was used in the form of Edison counter for measuring the quantity of electricity related to the first power supply system. Except in the area of ​​training and demonstration purposes, it has no practical significance. It is not to be confused with a voltmeter, colloquially referred to as a voltmeter.

The term originated from a name of Michael Faraday, who calls this measurement apparatus as " volta - electrometer ". In consequence named John Frederic Daniell building " voltameter ".

In principle, represents the voltameter one over time summing ammeter represents the SI unit for electric charge is the coulomb.

Species

A voltameter is an electrolytic cell in which the electric current through a chemical reaction takes place, eg evolution of gas or metal deposition. The actual measurement is then performed by depending on Coulometertyp

• Weighing of the chemical element which is deposited or released in a given time on one of the electrodes, or
• By volumetric measurement of the gas or
• By titration.

Metal voltameter

A metal is electrically dissolved and redeposited, and by weighing the dried electrodes, the charge can be determined. Mostly on the negative electrode, the cathode, deposited metal was weighed. Since the electrode was taken out and dried for weighing typically, these devices work discontinuously.

Silver voltameter

The Silbercoulometer is the most accurate type. It consists of two plates of silver in a solution of silver nitrate. When current is flowing, silver is dissolved at the anode and is deposited on the cathode. The cathode is weighed, the current flows in a measured time, then the cathode is weighed again, etc. The Silbercoulometer is therefore historically very significant because it served as the official primary standard for the measurement of current up to 1948.

Copper voltameter

Which is similar to the silver Kupfercoulometer voltameter, but the anode and cathode are made ​​of copper and the solution of copper sulfate dissolved in sulfuric acid. It is cheaper than the Silver voltameter, but somewhat less accurate.

Zinc voltameter

Zinc voltameter went into the history of electricity than the first one installed at the customer ammeters: Thomas Alva Edison it used in 1881 for current measurement, and let create the electricity bills of customers of its DC network so from 1883. To improve accuracy and control two zinc cells were connected in series, in turn, were not in the main circuit, but in parallel with a measuring resistor (shunt ) is connected in the main circuit.

Mercury voltameter

Wherein Quecksilbercoulometer a volume measurement. A particular embodiment utilizes a sliding drop of mercury, which was used in the first hour meter such as the Edison meter for measuring the quantity of electricity -related.

Gascoulometer

In this water was electrolyzed, with diluted sulfuric acid was used as an electrolyte in the rule. Therefore, these are also called sulfuric acid coulometer voltameter. Anode and cathode are preferably made of the corrosion-resistant platinum. In electrolysis, hydrogen produced at the cathode and oxygen at the anode. The two gases were collected in the oxyhydrogen voltameter as a mixture in a measuring glass. In Hofmann voltameter or Hofmann water electrolysis unit, the two gases are collected separately.

Since the volume of gas depends on the temperature, more accurate device were equipped with a thermometer, and the volume was converted to standard conditions. Because volume measurements are less accurate than mass measurements with a precision balance, Gascoulometer were also less accurate than Metallcoulometer. The great advantage of volume measurement is that no electrode must be removed, so that a quasi-continuous measurement is possible.

Other types

Another design represents the Iodcoulometer, wherein the amount formed at the anode was determined by titration of the iodine solution.

Load calculation with the aid of the electrochemical equivalent of

According to the Faraday's law the charge Q is proportional to the reacted compounds, and:

Additional charge Meters

The measurement of the electric charge can be done with lesser metrological effort by electronic circuits, such as the charge amplifier. This provides an amount of electric charge proportional electrical voltage.