An electrometer is a device used to measure the charge or potential difference of electricity. Available in a variety of designs, the instrument is essential in finding the voltage between two places in the electrical circuit. It can also be used to determine the level of electromagnetic interaction of subatomic particles.
The first electrometer was developed in the 1700s by Alessandro Volta and Abraham Bennet. This was a device that featured an electrode connected to two pieces of gold foil. The electrode was charged either through direct contact or by induction. The gold foil pieces would repel each other, indicating the presence of an electrical charge. The measurements were very crude and the device needed to be surrounded by a lead shielding to prevent leakage of the charge.
A number of new designs have been developed over the course of time. The most common use for electrometers today are to record ionizing radiation in the field of nuclear physics. One familiar device that utilizes the basic technology of the electrometer is known as a Geiger counter.
One design of a modern electrometer is an instrument that uses a vibrating reed. The basic design features a moving electrode that vibrates in relation to a fixed electrode. The combination of the two pieces creates a capacitor. When the distance between the two electrodes is altered, the electrical charge is forced in and out of the capacitor. The vibrating reed electrometer is highly useful in that the size of the instrument can be constructed at a very small level.
Another type of electrometer uses a vacuum tube. Within the tube, the current flows through a grid that offers high levels of input resistance. This is amplified using a polarized electrical device known as an anode circuit. This type offers very low levels of current leakage but suffers from damage when the salt from a human hand accumulates on the glass tube.
The most recent design of the instrument uses a solid-state amplifier that magnifies small currents for measurement. The most modern electrometers feature connections that can be hooked to external devices that will log data and create a display for viewing. The bonus of the solid-state design is that it is more accurate than other versions. It compares the internal voltage to the level of the input. Solid-state electrometers can also measure smaller levels of electric charge than other forms of the device.