Electrometer

November 1, 2021

The electrometer is a measuring instrument used to determine the electrical charge of a body. The first electrometer was invented in 1909 by Theodor Wulf, which measured the production of ions in a closed space. However, its direct predecessor was the electroscope , invented in the 18th century by the English researcher Abraham Benet.

The function of the electroscope has been the same as that of the electrometer. It worked with a metal rod that had two thin sheets of aluminum at one end and a sphere above the rod and when the sphere was brought close to an electrically charged object, the aluminum sheets repelled each other.

What is the Electrometer?

The electrometer works by the principle of electrostatic force , this is one of the four fundamental forces that acts by attracting or repelling (depending on their signs), bodies with electric charges. These interactions are called magnetic phenomena. The first electrometers are practically not used anymore but they describe their principle well.

Electrometers are boxes that have an insulated electrode that supports a gold foil; which will move on a graduated scale when it comes into contact with a loaded element, indicating its load. If electroscopes were more like indicators, electrometers are effectively meters of electrical charges.

Modern electrometers work with integrated circuits, which are small semiconductor structures and are built entirely of solid materials. Electrometers can measure minute currents reaching the femtoampere, the basis of the electrical unit. There are electrometers that use operational amplifiers for measurements.

What is the Electrometer for?

The electrometer is an instrument that measures electric charge, electric current, and potential difference , but what does this mean? Electric charge is the property of attraction and repulsion between particles by means of an electromagnetic field; the electric current is the flow of charge through a body and the potential difference is the impulse that makes the charge flow.

The electrometer measures indirectly induced charges on bodies. Its structure is made up of a faraday glass, to cancel out the effect of external fields on the internal electromagnetic field; a capacitor to store energy and a voltage amplifier, all interconnected to measure electrical charges.

There are several instruments that measure current, such as multimeters; the fundamental difference of the electrometer is that it measures extremely low voltages . The unit of the electric charge is the Coulomb and that of the current the ampere, when measuring the electrometer in femtoamperes, it is measuring thousands of electrons per second that flow in the sample.

Uses of the Electrometer

The electrometer is a highly specialized instrument. It is usually used in spectroscopy fields, which studies the relationship between electromagnetic radiation and matter; particle acceleration, high vacuum technology, which requires gas with a pressure below atmospheric and in atmospheric research, to mention those that use it the most.

To give you an example of the use of the electrometer, if you make use of an electric capacitor or capacitor, which is used to store electric charges, this in addition to having a charging current has a leakage current due to imperfections in the insulating material. This leakage is minimal but necessary to determine and for this the electrometer is used.

In fact, if you think about the first electrometer, Theodor Wulf devised it to measure the production of ions that, as atoms with electrical charges derived from the loss or acquisition of electrons, are measurable by the instrument. One of its most common uses, initially, was to detect ionizing radiation, although currently the dosimeter is used for this.

Types of Electrometers

There are three different types of electrometers , two of them invented by Lord Kelvin, a 19th century mathematician, physicist, and engineer who had prominent contributions to science, who published a description of how the electrometer works in 1857. The third is the Hakel filament electrometer, for which I will proceed to give you a brief description:

  • Lord Kelvin’s absolute electrometer

This electrometer gives an absolute measurement, through the measurement of the attraction weight of two plates placed horizontally in parallel, where one is smaller than the other and is covered by a ring. A voltage is applied between the plates and this will allow the displacement of the plates, which will lead to the measurement of potential.

  • Hankel Filament Electrometer

It works with a platinum filament that has a diameter of 1 or 2 mm and works by moving between opposite potentials. Measurement is done with a micrometer viewer. Detects differences of 1 to 100 volts.

  • Lord Kelvin’s Quadrant Electrometer

Metal box with four quadrants in which is suspended an eight-shaped needle that can be connected to the quadrants or an external source. The load to be measured is placed on the object directly or induced; When said object is loaded, it will rotate to one side or the other indicating the measurement.

These models are the classic electrometers from which the current ones are derived , which should be noted are made up of capacitors, amplifiers and circuits; being electrical measuring instruments that have great precision and multiple functionalities. However, its operating principles continue to be derived from the first models.

Characteristics of an Electrometer

Despite the differences in designs between the types of electrometers, they all base their measurement on the deviation given by a charge, and through this measure potential differences. The main features of the electrometer are the measuring electrodes and the deviation indicator . Although the modern ones are more like completely digital boxes.

Importance of the Electrometer

Currents less than 20 mA are not measurable with current measuring instruments such as a multimeter. This kind of measurement can only be performed with the electrometer that has a fetomapere resolution. These types of measurements are necessary in areas where ionized gases or electrical conduction are used in vacuum elements in order to be able to accurately control the charges and potential differences that are used.

The world of physics is extremely vast and employs an interrelationship between many areas; In order to keep track of all its elements over time, various instruments have been used that are perfected over time.

Dr. Loony Davis5
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Born and raised in Brussels in an English family, I have always lived in a multicultural environment. After several work experiences in marketing and communication, I came to Smart Water Magazine, which I describe as the most exciting challenge of my career.
I am a person with great restlessness and curiosity to learn, discover what I do not know, as well as reinvent myself daily, someone who is curious about life and wants to know. I enjoy sharing knowledge.
This is my personal project but I also collaborate in other blogs, it is the case, the most important web on water currently exists in the US, if you are interested you can read my articles here.

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