![]() The calibration process measures the linearity of the points measured which is the tendency they have to form a straight line when plotted. The resulting plot of the values measured in calibration would appear as follows: These four points can be represented on a graph, by plotting the expected ethanol content on the Y axis, and the electrical reading from the sensor on the X axis. For the purposes of this example, assume that the following standard values were presented to the machine, and the following values were measured from the light sensor: Ethanol Content IR Sensor Reading 0.01 3300 0.08 2820 0.20 2100 0.30 1500 (199) The machine recognizes that more ethanol will result in a smaller electrical signal, since the ethanol absorbs more of the infrared light. ![]() (198) The machine is provided the concentration of each of several different standards, and the machine then measures the amount of electricity generated by the sensor. ![]() To make the calculation of BrAC from the measurement of electricity from the sensor that detects light, the machine first constructs a logical graph of the values measured during calibration. (197) This does not mean that ethanol only absorbs infrared light at this selected frequency, but rather, that after the machine is done examining the measurements from all of the frequencies provided, the machine will simply compute the amount of ethanol using a simple algebraic equation. (196) The companies often refer to this as the "ethanol channel", or the "Ethanol frequency" for measurement. Most breath-test machines utilize one of the measured infrared light frequency responses as the electronic signal that computes the amount of ethanol in the sample. Using the Calibrated Measurements to Compute BrAC
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