Dummy load
The term dummy load (including ballast, Eng. Dummy load ) denotes an artificial load in the electronics and high-frequency technology, which substitute for testing to simulate the electrical properties of a real assembly, load or antenna to one to be examined unit (power supply, transmitter) is connected.
DC - equivalent loads
The testing of the electrical properties and the control behavior at power supplies requires to achieve reproducible results usually the load of the specimen with a defined, simulated and fluctuations, consumer. Such a consumer whose electrical properties, the auditor can pretend and is also referred to as electronic load is a dummy load. The converted him into electrical power is dissipated as heat or - also fed back into the grid - at high power.
Dummy load for AC voltages
RF and Microwave
The test of high-performance radio frequency transmitters and amplifiers requires mandatory to connect a load to the transmitter, otherwise the transmitter can be destroyed by mismatch ( VSWR >> 1 ). In any case, no defined conditions are met with open transmitter output; a measurement of the transmission power is not possible. The connection of an antenna for a metrological examination of a transmitter is ruled out but as an antenna is not a viable load for transmitter measurements over a wider frequency range because of their frequency-dependent impedance. In addition, the transmitter signal is through the use of a real antenna actually radiated and other spectrum users might be disturbed. It is therefore useful to a (non -radiating ) resistor to charge the transmitter and antenna replacement. This resistance must be such that it retains its properties even at high frequencies, ie, has no capacitive or inductive reactive components. Furthermore, this resistance must be able to fully implement the transmission power offered to him in the heat without taking damage. The last two requirements ( high-frequency suitability combined with high load capacity ) include a technically challenging problem. An impedance- correct design in conjunction with cooling measures ( either oil or dry using a large heat sink) is complex.
Colloquially equivalent loads are designated under RF technicians as artificial antenna, dummy load and waveguides as a wave sink.
A dummy load is also necessary in order to calibrate a SWR meter can.
Low frequency
Audio Amplifier
To test audio amplifier and output stages and to specify, instead of the speaker, a dummy load is connected. In order to create conditions defined at the output of the amplifier it is terminated with a resistor of appropriate size and load capacity. It used purely resistive impedances, although real speakers or boxes also have complex impedance shares. As a resistive load can be employed naked or cemented wire wound resistors, since their harmful for high frequency applications, parasitic inductance in the audio - frequency range is not critical.
While transistor amplifier can also be operated with an open end, is important with output transformer of the permanent connection of a dummy load for measurements on some audio tube amplifiers, such as amplifier without a load can be damaged after booting.
Lately, adjustable and automated Dummy loads have been developed for the test of audio amplifiers. These allow, for example, measurements in automated test environments.
Mains voltage
For testing of generator sets, inverters and generators requires a dummy load that simulates an electrical line voltage consumers.
Dummy load as a protective device
Equivalent loads are used for example to charge controllers to protect the generator. To prevent the generator runs unloaded, he shall not be separated from a fully charged battery bank but implemented its performance in the dummy load. This avoids, for example, in wind generators that they be destroyed due to high speeds at idle itself.