Spark gap
A spark gap consists of an arrangement of two
Spark gaps were used historically in early electrical equipment, such as
Breakdown voltage
For air, the breakdown strength is about 30 kV/cm at sea level.[1]
Spark visibility
The light emitted by a spark does not come from the current of
Applications
Spark gaps are essential to the functioning of a number of electronic devices.
Ignition devices
A spark plug uses a spark gap to initiate combustion. The heat of the ionization trail, but more importantly, UV radiation and hot free electrons (both cause the formation of reactive free radicals)[citation needed] ignite a fuel-air mixture inside an internal combustion engine, or a burner in a furnace, oven, or stove. The more UV radiation is produced and successfully spread into the combustion chamber, the further the combustion process proceeds.[citation needed]
The
Protective devices
Spark gaps are frequently used to prevent
Smaller spark gaps are often used to protect sensitive electrical or electronic equipment from high-voltage
Small spark gaps are very common in telephone switchboards, as the long phone cables are very susceptible to induced surges from lightning strikes. Larger spark gaps are used to protect power lines.
Spark gaps are sometimes implemented on
High speed photography
A triggered spark gap in an air-gap flash is used to produce photographic light flashes in the sub-microsecond domain.
Radio transmitters
A spark radiates energy throughout the
Sphere gap for voltage measurement
A calibrated spherical spark gap will break down at a highly repeatable voltage, when corrected for air pressure, humidity and temperature. A gap between two spheres can provide a voltage measurement without any electronics or voltage dividers, to an accuracy of about 3%. A spark gap can be used to measure high voltage AC, DC, or pulses, but for very short pulses, an
Power-switching devices
Spark gaps may be used as electrical switches because they have two states with significantly different electrical resistance. Resistance between the electrodes may be as high as 1012 ohms when the electrodes are separated by gas or vacuum which means that little current flows even when a high voltage exists between the electrodes. Resistance drops as low as a 10-3 ohms low when the electrodes are connected by plasma which means that power dissipation is low even at high current. This combination of properties has led to the use of spark gaps as electrical switches in pulsed power applications where energy is stored at high voltage in a capacitor and then discharged at high current. Examples include pulsed lasers, railguns, Marx generators, fusion, ultrastrong pulsed magnetic field research, and nuclear bomb triggering.
When a spark gap consists of only two electrodes separated by gas, the transition between the non-conducting and conducting states is governed by Paschen's law. At typical pressure and electrode distance combinations, Paschen's law says that Townsend discharge will fill the gap between the electrodes with conductive plasma whenever the ratio of the electric field strength to the pressure exceeds a constant value determined by the composition of the gas. The speed with which pressure can be reduced is limited by choked flow, while increasing the electric field in a capacitor discharge circuit is limited by the capacitance in the circuit and the current available for charging the capacitance. These limitations on the speed with which discharge may be initiated mean that spark gaps with two electrodes typically have high jitter. [6]
Triggered spark gaps are a class of devices with some additional means of triggering to achieve low jitter. Most commonly, this is a third electrode, as in a trigatron. The voltage of the trigger electrode can be changed quickly because the capacitance between it and the other electrodes is small. In a triggered spark gap, gas pressure is optimized to minimize jitter while also avoiding unintentional triggering. Triggered spark gaps are made in permanently sealed versions with limited voltage range and in user-pressurized versions with voltage range proportional to the available pressure range. Triggered spark gaps share many similarities with other gas-filled tubes such as thyratrons, krytrons, ignitrons, and crossatrons.
Triggered vacuum gaps, or sprytrons, resemble triggered spark gaps both in appearance and construction but rely on a different operating principle. A triggered vacuum gap consists of three electrodes in an airtight glass or ceramic envelope that has been evacuated. This means that, unlike a triggered spark gap, a triggered vacuum gap operates in the parameter space to the left of the Paschen minimum where breakdown is promoted by increasing pressure. Current between the electrodes is limited to a small value by field emission in the non-conducting state. Breakdown is initiated by rapidly evaporating material from a trigger electrode or an adjacent resistive coating. Once the vacuum arc is initiated, a triggered vacuum gap is filled with conductive plasma as in any other spark gap. A triggered vacuum gap has a larger operating voltage range than a sealed triggered spark gap because Paschen curves are much steeper to the left of the Paschen minimum than at higher pressures. Triggered vacuum gaps are also rad hard because in the non-conducting state they do not contain any gas that could be ionized by radiation. [7]
Insect control
They are also used as insect zappers. The two electrodes are implemented as metal lattices placed a slightly too far apart for the voltage to jump. When an insect ventures between the electrodes the gap distance is reduced by the insects body, being conductive, and a spark discharge occurs to electrocute and burn the insect.
In this use the spark gap mechanism is often used in conjunction with a bait, such as a light, to attract the insect into the spark gap.
See also
- Arc lamp
- Arcing horns
- Corona discharge
- Electric arc
- Ignition system
- Model T Spark Coil
- List of electronics topics
- Plasma arc loudspeakers
- Radar
- Spark-gap transmitter
- Spark plug
- Spark spread
- Tesla coil
- Vacuum arc
- Paschen's law
References
- .
- ^ "Boeing: Space Shuttle Main Engine Orientation" (PDF). Boeing. June 1998. Retrieved 16 November 2019.
- ^ [1] Transient Protection Products, Gas Tubes, Hybrid Protection Systems | rated up to 20,000 amps ... sealed from dust and moisture ... some have small amount of amounts of Tritium Backfill Gas (10 microcuries) | Reynolds Industries Incorporated
- ^ "A guide to designing for ESD and EMC" (PDF). NXP Semiconductors. January 19, 2010. Archived (PDF) from the original on August 3, 2019.
- ^ Ryan, Hugh M. (ed)
High Voltage Engineering and Testing (2nd Edition), Institution of Engineering and Technology 2001, ISBN 978-0-85296-775-1pages
- ^ "Triggered Spark Gap Design". Retrieved 17 February 2019.
- ^
Gas Discharge Closing Switches. Springer Science+Business Media, LLC. 1990. ISBN 978-1-4899-2132-1.
External links
Jacob's Ladder videos: