Dummy load
From Wikipedia, the free encyclopedia
A dummy load is a device used to simulate an electrical load, usually for testing purposes.
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[edit] Radio
In radio this device is also known as a dummy antenna or a radio frequency termination. It is a device used in place of an antenna to aid in testing a radio transmitter. It is substituted for the antenna while adjusting the transmitter, so that the transmitter does not interfere with other radio transmitters during the adjustments. [1] If a transmitter is tested without a load, such as an antenna or a dummy load, the transmitter could be damaged. Also, if a transmitter is adjusted without a load, it will operate differently than with the load, and the adjustments may be incorrect.
The dummy load ordinarily should be a pure resistance; the amount of resistance should be the same as the impedance of the antenna or transmission line that is used with the transmitter (usually 50 Ω or 75 Ω).[2] The radio energy that is absorbed by the dummy load is converted to heat. A dummy load must be chosen or designed to tolerate the amount of power that can be delivered by the transmitter. [3]
The ideal dummy load provides a standing wave ratio (SWR) of 1:1 at the given impedance.
- See also: Antenna (radio) and Standing wave ratio
[edit] Audio
When testing audio amplifiers, it is common to replace the loudspeaker with a dummy load, so that the amplifier's handling of large power levels can be tested without actually producing intense sound. The simplest is a resistor bank to simulate the voice coil's resistance.
For loudspeaker simulation, a more complex network is more accurate, however, as actual loudspeakers are reactive and non-linear. There are many designs for loudspeaker simulators, which emphasize different characteristics of the actual speaker, such as the voice coil's inductance, mechanical suspension compliance, and cone mass.
[edit] Power supplies
There are also dummy loads for power supplies, known as load banks.
An electronic load (or e-load) is a device or assembly that simulates loading on an electronic circuit. It is used as substitute for a conventional ohmic load resistor.
As counterpart to a current source, the electronic load is a current sink. When loading a current source with a fixed resistor one can set one determined load current by the connected load resistor. The characteristic of the electronic load is that the load current can be set and varied in a defined range. The load current is regulated electronically.
The electronic load consumes electric energy and in most cases transforms it into heat energy. Fans or water-cooled elements are used as coolers. Under certain conditions, energy-recycling into the public power supply system is also possible.
Electronic loads are used in diverse applications, particularly for the test of power supplies, batteries, solar and fuel cells, generators. AC loads are used to test transformers, uninterruptible power supplies (UPS) or onboard power supplies. The equipment and power spectrum of such electronic loads begins with simplest circuits consisting in general of a potentiometer for current setting and a transistor circuit for power transforming. Further develeoped electronic loads supply several operating modes, in most cases constant current, voltage, power and resistance. Nowadays, the equipment offers furthermore the possibility for being controlled analogous or by PLC or remotely by a PC. Settings and measured values such as input voltage and actual load current are indicated on a display.
[edit] References
- ^ (1990) in Kleinschmidt, Kirk: ARRL Handbook for the Radio Amateur. Newington, Connecticut: American Radio Relay League, 25-21 through 25-23.
- ^ (1990) in Kleinschmidt, Kirk: ARRL Handbook for the Radio Amateur. Newington, Connecticut: American Radio Relay League, 25-21.
- ^ (1990) in Kleinschmidt, Kirk: ARRL Handbook for the Radio Amateur. Newington, Connecticut: American Radio Relay League, 34-22 through 34-28.
[edit] Further reading
- Ausias Garrigós and José M Blanes. "Power MOSFET is core of regulated-dc electronic load", EDN, 2005-03-17.
- Martin Rowe. "Loads need calibration, too", Ensuring power supply accuracy, Test and Measurement World, 2005-12-01.
- M. B. Borage, S. R. Tiwari, and S. Kotaiah (2003-07-07). "Inductive electronic load for testing of magnet power supplies in particle accelerators". Review of Scientific Instruments 74 (12): 5194–5196. doi:.
- Meng-Yueh Chang, Jiann-Yow Lin, Shih-Liang Jung, Ying-Yu Tzou (1997-06-27). "Design and implementation of a real-time lossless dynamic electronic load simulator". 28th Annual IEEE Power Electronics Specialists Conference 1: 734–739. ISBN 0-7803-3840-5.
- B. Singh, S.S. Murthy, S. Gupta (2004-01-14). "Analysis and implementation of an electronic load controller for a self-excited induction generator". Proceedings of Generation, Transmission and Distribution 131 (1): 51–60.
[edit] See also
[edit] External links
- TDI Dynaload - Electronic Dynamic Loads
- Bird Electronics - Power terminations and loads
- Coaxial Dynamics - Power terminations and loads
- Amplifier dummy load - Rane Pro Audio reference
- Measuring Loudspeaker Parameters - Elliott Sound Products
- Speaker impedance - ePanorama.net
- EB5HTC Dummy Load 108W manual - How to make a dummy load 108W
