WorldWide Drilling Resource

47 WorldWide Drilling Resource ® AUGUST 2015 Using Time by Britt Storkson Owner, P2FlowLLC We are, in a sense, slaves to time. Much of our lives are governed by “the clock”. We have to be at certain places at certain times, or do certain things at certain times. Many sports events such as football, basketball, and soccer are timed. Even the voltage you get from your power source is timed turning “on” and “off” (oscillating) at 60 cycles per second, in this country. It’s 50 cycles some other countries. Microprocessors are no different. All microprocessors have a “clock” of some sort. There are several types of microprocessor clock sources to choose from depending on the timing accuracy desired. One of the most common and stable clock sources is a microprocessor crystal. When properly driven, the microprocessor crystal oscillates (turns on and off) at a fixed frequency. By “on” and “off” we mean goes to zero voltage and then quickly up to a certain voltage, then back down to zero voltage again. This full transition from low volt- age to high voltage and back to low voltage is called one cycle. One cycle per second is called one hertz. Crystal oscillators come in a wide variety of frequencies and are fairly stable over time and temperature. One of the most com- mon crystals now in use is a 32,768 hertz watch crystal. It’s also called a 32.768 kHZ crystal or kilohertz with kilo meaning 1000. These are often used in inexpensive single-battery wall clocks you can get for less than $10. Internal circuitry in the wall clock “counts” the number of cycles the crystal makes and, when the count reaches 32,768, it resets to zero and moves the second hand on the clock up one second. The minute hand is geared such that it moves up one when the second hand rotates 60 times, and the hour hand moves up one when the minute hand rotates 60 times. These crystal oscillators are very low power, consuming something on the order of 1 microwatt - 1 millionth of a watt - of power. That’s why they only need a single-cell battery (often an AA style 1.7-volt battery) and also why they last so long...typically one year or more. Microprocessors are great for counting pulses (voltage transitions) from any number of sources. For example, we can make a tachometer by counting the number of times a shaft rotates, and evaluating it every second. So if we count 60 revolutions per second we have one revolution per minute (rpm). Typically for this application, we count 60 revolutions; and when that happens, we add “1” (increment) to another counter and clear (reset to zero) the revolution counter. Then when our oscillator timer indicates 1 second, we update the display to show the new value and then start the process over again. Time is important, and microproces- sors make it possible to measure events relative to time. This gives us information we would not normally have to make deci- sions so the equipment - such as an auto- mobile engine - will be protected from overspeed and other conditions which could damage it. We can use time to our advantage. Britt Britt Storkson may be contacted via e-mail at michele@ worldwidedrillingresource.com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