4.3. Function Generator

The function generator makes the ALx Series MagnaLOAD DC electronic load sink current according to an internally generated waveform. This feature simplifies dynamic-load test setups since the generation is self contained and conveniently customized through the front panel menu system. Each of the function types available have a different signal-processing algorithm for accepting input parameters and outputting a periodic signal.

The function generator is enabled by choosing it as a Setpoint Source through menus System Settings - Setpoint Source - Function Generator. Once enabled, all set point changes from other sources are ignored. The generator algorithm, selected through menus Function Generator - Function Type, is subject to limitations of the sample rate and look-up table size. The algorithm can update at a rate of 0.5 ms. As such, the period is limited such that 4 samples are output per period (2 ms). The maximum period is restricted to 65000 ms. Set point related parameters (Amplitude, LoLevel, Offset, etc.) are limited to the product’s rated current.

4.3.1. Sinusoid

The sinusoid function produces its waveform using the direct digital synthesis (DDS) method. Set points are loaded from a 1024 point sinusoid lookup table and scaled at fixed-sample intervals. The function is selected through menus Function Generator - Function Type - Sinusoid. The amplitude is set through menus Function Generator - Function Type - Sinusoid Parameters - Amplitude(Adc). From the same parent menu, offset and period are set in menus Offset(Adc) and Period(ms), respectively. These parameters and their effect on the waveform are illustrated in Fig. 4.1.

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Fig. 4.1 Sinusoid Waveform Parameters

4.3.2. Square

The square function produces its waveform by logically changing set points after a programmed period of time. The function is selected through menus Function Generator - Function Type - Square. The low-level set point is programmed through menus Function Generator - Function Type - Square Parameters - LoLevel(Adc). From in the same parent menu, offset and period, in menus Offset(Adc) and LoPeriod(ms), respectively, are programmed. These parameters and their effect on the waveform are illustrated in Fig. 4.2.

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Fig. 4.2 Square Waveform Parameters

4.3.3. Step

The step function behaves similarly to the Square Function, but step points cycle manually by pressing the start button. The first time the start button is pressed, the MagnaLOAD electronic load is enabled, and regulates to the parameter saved in LoLevel(Adc). Pressing the start button again changes the set point to HiLevel(Adc). Pressing the button a third time cycles back to LoLevel(Adc). The parameter effects on the waveform are illustrated in Fig. 4.3.

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Fig. 4.3 Step Waveform Parameters

4.3.4. Ramp

The ramp function produces its waveform by logically changing set points after a programmed period of time, while maintaining specified rise and and fall time. The function is selected through menus Function Generator - Function Type - Ramp The low level set point is programmed through menus Function Generator - Function Type - Ramp Parameters - LoLevel(Adc). From the same parent menu, the high level and rise and fall periods, HiLevel(Adc), RiseTime(ms) and FallTime(ms), are set respectively. These parameters and their effect on the waveform are illustrated in Fig. 4.4.

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Fig. 4.4 Ramp Waveform Parameters