Electrometer - what is it? There are many different types, ranging from rare mechanical hand tools to high-precision devices. Modern electrometers and other measuring devices are assembled on the basis of a vacuum tube or solid-state technology. They can be used to measure voltage and charge with very low leakage currents, up to 1 femto ampere. An electroscope is a simpler device. It works on similar principles, but shows only the relative magnitudes of the stresses. And what does an electrometer and other instruments measure?
History of this device
The very first potential meter can be called "Early Square" or simply "Square". Although the term ultimately referred to the version of Kelvin, it was first used to describe a simpler device. And what does an electrometer measure and what does it consist of?
It is made of a vertical tree trunk to which an ivory semicircle is attached. From the center, a light cork ball hangs on a hinge. When the instrument is placed on a charged body, the stem engages and repels the cork ball. The magnitude of the repulsion can be read from a graduated semicircle, although the measured angle is not directly proportional to the charge. Among the first inventors were William Henley and Horace-Benedict de Saussure.
And who was the “pioneer” of electroscopes?
But what is an electroscope and an electrometer, and which of them was better? The very first electroscope with a gold leaf was definitely the very first. Such a device can be found in the real world at some scientific conferences, but basically it has been universally replaced with a more technological version. Unlike an electrometer, it more often played the role of a sensor than a measuring device.
The instrument itself consists of two thin sheets of gold foil suspended from an electrode. When it is charged by induction or contact, the leaves acquire the same electric charges and repel each other due to the Coulomb force. Their separation is a direct indicator of the accumulated clean energy. Pieces of tin foil can be glued onto the glass opposite the leaves so that when the leaves completely diverge, they can fall into the ground. Petals can be enclosed in a glass "envelope" to protect them from drafts. To minimize charge leakage, this envelope is insulated. Another cause of leakage is ionizing radiation, therefore, to prevent it, the electrometer should be surrounded by a lead shield.
The tool was developed in the XVIII century by several researchers, including Abraham Bennet and Alessandro Volta.
Models from Peltier and Bonenberger
The Bonenberg measuring device consists of one gold leaf suspended vertically between the anode and cathode of the dry pile. Any charge transferred to gold leaf causes it to move to one or the other pole. What does a Bonenberg electrometer measure? The sign of the charged particle, as well as its approximate value.
A Peltier electrometer uses the shape of a magnetic compass to measure deflection, balancing static force with a magnetic needle.
Modern devices
A modern electrometer is a highly sensitive voltmeter, the input impedance of which is so large that the current flowing into it can be considered equal to zero for most household tasks.
What does an electrometer measure and what is its resistance? The actual value of the input resistance for modern devices is about 10 14 Ohms, compared with 10 10 Ohms for nanovoltmeters. Due to the extremely high input impedance, special design solutions must be applied to avoid current leakage.
Among other applications, electrometers are used in experiments in nuclear physics, as they are capable of measuring the tiny charges left in a substance through ionizing radiation. The most common use of modern devices is to measure radiation using ionization chambers in instruments such as Geiger counters.
Valve electrometer
Valve versions use a specialized vacuum tube with a very high gain and input impedance. The input current can flow into the impedance network, and the voltage generated in this way is significantly amplified in the anode (plate) circuit. Valves designed for use with electrometers have leakage currents of only a few femtoamps (10-15 amperes). Gloved hands should be used to touch these valves, as salts remaining on the glass shell can create leak paths for these tiny currents.
In a specialized circuit called an “inverted triode,” the roles of the anode and grid are reversed. This places the control element at the maximum distance from the space charge region surrounding the filament, minimizing the number of electrons collected by the control circuit, and thus reducing the input current to the smallest value.
The most advanced electrometer
The most advanced measuring instruments consist of a solid-state amplifier using one or more field effect transistors, connections for connecting external measuring devices, and, as a rule, connections. For a solid-state electrometer, the photo above.
The amplifier increases a small current to simplify its measurement procedure. External connections usually have a coaxial or triaxial design and allow the installation of diodes or ionization chambers for measuring ionizing radiation. Connections to a display or data recording equipment allow the user to view or record data for later analysis.
Electrometers intended for use with ionization chambers may include a high voltage power supply, which are also used to bias the ionization chamber.