Consider the development of a \"through-beam\" photoelectric sensor. A through-b
ID: 2229090 • Letter: C
Question
Consider the development of a "through-beam" photoelectric sensor. A through-beam photoelectric sensor consists of a transmitting light source and a photo receiver. The transmitter and the receiver are lined up. When the beam is not broken, light from the transmitter hits the receiver and turns on the output transistor from the receiver. Their purpose is to detect objects as the objects break the beam. What are the operational parameters that must be determined before starting to design a through-beam photoelectric sensor?Explanation / Answer
In 1964 an electronic quartz timing system was used for the first time in internationalevents, thereby improving timing accuracy to 0.01 of a second. The computerised timingsystems used in events today have increased the accuracy to less than 0.001 of a second,which is 10 times the accuracy required under the rules.Judging very close running races remained a problem until photo-finish video cameraswere used at the finish line. (Originally, film-based cameras were used, but this meant thatathletes and spectators had to wait until the film was developed before they knew the result.)The introduction of the vertical line-scanning video system in 1991 totally removed human judgement and reactions from the timing and judging of world class running events. Thestarter's pistol is linked to a transducer, which detects the sound made when the starter pullsthe trigger. The transducer is connected to a timing computer, which starts to countimmediately it receives the signal.Connected into this system is a high quality video camera located at the finish line. Thisproduces the official time and a video image of the athletes as each one passes the finish line.The video camera scans a thin line aligned with the finish line up to 3000 times per second.The video image of each athlete as they actually cross the line is shown superimposed with agrid that records the time for each competitor. This system allows judges to declare the resultmore quickly and more accurately. (Two parallel infra-red beams also located at the finishline are directly linked to display boards within the stadium. They provide the audience withan instant but unofficial time for the race.)