Electrostatic voltmeter

The electrostatic voltage measuring device , also known as electrostatic voltmeter is designated, an electrical voltage measuring device which, according to the electrostatic principle operates. The measurement is traced back to the physical size of a force .

For further powerless measurement methods of electrical voltage and electrical field strength, see also electrometer amplifiers and rotation voltmeters .

General

Principle of an electrostatic voltmeter with spring, display and electrodes

The effect of the force on electrical charges, which is expressed in Coulomb's law , is used. In the case of equilibrium, the force F _el on the electrical charge on the electrodes is equal to the spring force F _spring , which is used for resetting:

{\ displaystyle F _ {\ text {el}} = F _ {\ text {Feder}} = 0 {,} 5 \ cdot {\ frac {\ varepsilon _ {0} AU ^ {2}} {d ^ {2} }} = D \ cdot x}

where d is the distance between the electrodes, A is the area of the electrodes, ε _{0 is} the dielectric constant and D is the spring constant . The deflection x is made visible on a scale and represents an expression for the electrical voltage U applied .

In the case of direct voltage , the display is independent of the polarity; in the case of alternating voltage , the rms value is displayed due to the mechanical inertia ; however, surge voltages cannot be recorded. Due to the quadratic voltage dependence of the force equation, a relatively high accuracy of up to 0.1% is only given with high electrical voltages. The voltage range can be selected within certain limits by varying the distance d between the measuring electrodes.

species

Strong Schröder voltmeter

Deflection mechanism of a Starke Schröder voltmeter

The Starke Schröder voltmeter is an electrostatic voltage measuring device which is used in high voltage technology. The electrostatic force causes a small mirror to move on one of the electrodes, which deflects a beam of light. This deflection, which is proportional to the voltage, can be read on a scale.

Starke Schröder voltmeters have a simple design up to voltages of a few 10 kV. At high voltages above 100 kV, pressurized gas-insulated designs are used in order to keep the mechanical dimensions of the electrodes and interference effects due to edge effects small. Due to their mechanical sensitivity, these measuring devices are usually only used in high-voltage laboratories .

Electroscope

→ Main article: electroscope

In the electroscope, both electrodes are at the same potential and repel each other when voltage is applied, one electrode being designed as a pointer and serving as a display. In some devices, the force of the electrostatic repulsion of the electrodes is balanced by the force of gravity acting on the pointer .

literature

Andreas Küchler: High voltage technology: Basics - Technology - Applications . 3. Edition. Springer, 2009, ISBN 978-3-540-78412-8 .