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This DC electronic load is intended for use in investigating the behaviour of many different types of DC power sources such as batteries, solar cells, fuel cells or wind generators, as well as electronic Power supply units. It operates over the current range 0 to 80 Amps and voltage range 0 to 80 Volts with a power dissipation capability of up to 300 Watts. It is designed to have very low internal resistance to allow operation at high currents with low voltage drop. The voltage of the source can be sensed either internally for convenience or externally for better accuracy. A low voltage dropout facility is provided to protect sources such as batteries from damaging levels of discharge by reducing the load current when the source voltage falls below the dropout threshold. The unit provides five different operating modes: constant current, constant voltage, constant power, constant resistance and constant conductance. The value of the chosen constant parameter is set by 10-turn controls on the front panel. An internal transient Generator can repeatedly switch the load between two different operating levels set on separate 10-turn controls. The frequency and duty cycle of the transients can be set over a wide range. The transients can also be initiated by an external logic signal. The transitions between the levels have a true linear slewing characteristic in all modes; the slew-rate is adjustable over a wide range. An external control voltage can also be used to set the level of the load. Any desired waveform can be applied; the internal slew rate control circuit remains active. Two 4-digit meters can be switched to display either the level settings, the transient Generator parameters, the measured values of Volts & Amps or the equivalent Watts & Ohms. A monitor output providing a voltage proportional to the current flowing allows the behaviour of a source to be viewed on an Oscilloscope or external meter. The unit is fully protected against excessive current, power dissipation or internal temperature, and minimises audible noise by automatically controlling the fan speed according to the power dissipation.