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Arb Files as Controllers

Besides using Arb files instead of conventional signal waveforms like Sine, you can use them as AM, FM, Phase/Slope/Width, or Burst modulation sources to control other waveforms.

For example, you may want to simulate the signal from an engine crankshaft position sensor, for testing an Electronic Control Unit (ECU) or Module (ECM) without an engine present.

(Note that the Engine_Sim macro mini-app automates this process so you don't actually need to use the procedure below; it's an example of the basic technique.)

You can use the procedure described in Creating Pulse-Train Arbs to create the basic sensor signal. That Arb simulates one complete revolution of the crankshaft, so you'd set its Tone Freq to 10 Hz to simulate an engine at 600 RPM, or 100 Hz for 6000 RPM.

You can use a second Arb to create a complete test schedule of various engine accelerations, decelerations, and steady speeds. This Arb will run much more slowly, such that one cycle is the duration of the overall test... perhaps many minutes or hours.

In this example, the controller Arb would be loaded to Stream 0 and the sensor Arb to Stream 1. (A modulator must always be on a lower-numbered stream than the stream it modulates.) Then in Stream 1, open the FM control dialog and set FM Source to Stream 0.

Suppose the controller Arb on Stream 0 produces a wave that covers a range of 0 to 100% over the course of the test cycle, and Stream 0 Level is set to 100%. If you want that range to represent 0 to 6000 RPM, then that is equivalent to a 0 to 100 Hz frequency range, so set Stream 1 Tone Freq to 0 Hz, and FM Deviation to 100 Hz.

(Note that Engine_Sim uses an Arb with two crank revolutions per Arb cycle, so that 50 Arb cycles per second is equivalent to 100 crank revolutions per second or 6000 RPM, so it sets FM Deviation to 50 Hz.)

Then set Stream 0 Tone Freq to the reciprocal of the test duration in seconds. (1 minute = 1/60 Hz = 0.01667 Hz. 1 hour = 1/3600 Hz = 0.000278 Hz.)

Of course, you probably don't want the simulated engine speed to go right down to 0, so this controller Arb would actually only go as low as the idle RPM. If that's 600 RPM, the Arb would actually go from 10% to 100% instead of 0 to 100%.

Another way to set this up would to create the controller Arb to actually go from 0 to 100%, but set the Stream 1 Tone Freq to the equivalent idle frequency (10 Hz, in the above example), and set FM Deviation to the maximum minus the idle (100 - 10 = 90 Hz).

In a similar fashion, other applications can use Arbs to control the amplitude of the main waveform using AM. For example, an industrial shake test could control the test amplitude with one Arb, and the test frequency with another. You might have the amplitude Arb on Stream 0, and the frequency Arb on Stream 1, and have them control AM and FM, respectively, on Stream 2.

There is no problem using both AM and FM acting on the same stream. Just set the AM Source to use Stream 0 and the FM Source to use Stream 1.

In this example, you'd probably want these to control a simple Sine on Stream 2 to drive the shaker, but in other cases you might want a third Arb here.

To create the Arb files, see Arb_From_List Macro Mini-App, Creating Arb Files with the Generator, and also Creating Arb Files From Text.

See also Random Selection of Arb Values, Wave Dialog, Arb Wave.


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