![]() Consider an entire system that collects data, not just the ADC. System has no actuator because it simply measures the measurand in Measurand in the real world to a desired value while the data x(t) is the time-varying signal we are attempting to measure. Figure 14.1 shows the data flow graph for a data Like sound, distance, temperature, force, mass, pressure, flow, lightĪcceleration. To measure distance to an object (EE319K skips this). Use the Central Limit Theorem to improve signal to noise ratio.Theorem to cases where we use the ADC to sense information. Quantization, range, precision and resolution. Transducers: conversion of physical to electrical.ĭigital computer to sense its analog world. We define the rate at which we sample as the sampling rate, and use the symbol fs.ĪDC, software, PWM output and motor interfaces to implement intelligent ![]() Interrupts to sample the ADC at a fixed rate. More specifically, we present a technique for theĪnalog inputs using an analog to digital converter (ADC). ![]() This chapter we will focus on input devices that we use to gatherĪbout the world. System uses its input/output devices to interact with the external Throughout this course we have seen that an Modified to be compatible with EE319K Lab 8 As engineers, we have to determine if the level of imperfection will be acceptable for the application.14: Analog to Digital Conversion, Data Acquisition and Control We should stress the point that nothing is perfect. Hopefully, this example helped to show how accuracy and repeatability are commonly confused in motion control applications. At this point, it may be better to add another measuring device, like a linear encoder, that has a guaranteed accuracy. We could map the positional error throughout the entire travel range and make a calibration table, but that would be time-consuming and there is a lot of opportunity for mistakes. He wants to be able to enter any length in millimeters on an HMI screen and have the system cut that length. So happy in fact that now he wants to use this system to cut all of his wire. The solution worked! It turns out that even though the application called for positional accuracy, it could be accomplished with repeatability and a little calibration. This saved Bert a lot of money because a system that has an accuracy of 0.1mm at 900mm would be much more expensive. So instead of 90 turns of the screw, we will program the motor to rotate 89.97 times. Maybe if we shoot for 899.7mm, we will actually hit 900mm. What if we calibrate the system? The +0.3mm error can be accounted for by reprogramming the move. So, what do we do now? Do we trash this system and start from scratch? Not so fast. Positional accuracy is dependent on the stroke length and as the actuator travels 900mm, it is not uncommon for it to be off a few tenths of a millimeter. The reason? Nothing is perfect, not even a precision ground ball screw. Even though the system has a resolution of 0.005mm and a repeatability of 0.02mm, the actuator was still off by 0.3mm after traveling 900mm. Repeatability was mistaken for accuracy, that’s how. This is a very common problem, and these are real world numbers. But it seems like all the measurements are off by about +0.3mm. The measurements were all very close, within 0.01mm of each other, so the repeatability is very good and within catalog specification. Three parts were measured and the values were 900.305mm, 900.295mm, and 900.300mm. Resolution: The smallest difference that can be measured.Īfter running the machine for a while it is discovered that the parts are too long.Repeatability: How close a group of measurements are to each other. ![]()
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