If a picture is worth a 1,000 words, then a flow chart should be good for at least 1,001. Here is how the Speed and Distance testing process works on the g-Analyst.
As you can see, the first decision point is whether or not the current g-reading is greater than the Start_G setting. Why? Because of integration error.
The g-Analyst integrates acceleration to obtain velocity and integrates velocity to obtain distance. As with any process, there is some error involved. The velocity error is proportional to time. The distance error increases with time^2. To minimize this error, the g-Analyst waits until the vehicle begins to move (g-reading > Start_G).
Where should Start_G be set? A good rule-of-thumb is to set Start_G at no more than 1/2*(vehicle max. acceleration). Lower is better, but not so low that the test 'triggers' before you start.
Example:
Standard Passenger Car: Start_G = 0.15g to 0.20g
Performance Passenger Car: Start_G = 0.20 to 0.30g
The next decision point allows you to tailor the timing of the test.
Start_Speed can be used for 'magazine tests,' where the value is typically 1 MPH.
Start_Distance can be used to replicate the 'roll-out' (distance between a vehicle's tires and the timing lights) at a drag strip.
Start_Speed and Start_Distance are not usually used together.
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