电子信息类专业英语,http:/www.cmpbook.com,机械工业出版社同名教材配套电子教案,温丹丽 高源 制作,机械工业出版社 http:/www.cmpbook.com,1. What are the major functions of a simple frequency counter? 2. How does the frequency counter measure frequencies?,Passage One Digital Counter and Digital Frequency Counters,Passage One Digital Counter and Digital Frequency Counters,Words and Expressions emerge v. 显现，脱出 interval n. 时间间隔 auto ranging 自动量程,机械工业出版社 http:/www.cmpbook.com,Passage One Digital Counter and Digital Frequency Counters,Text Electronic Digital Counter Common to all digital instruments is the electronic digital counter. The electronic counter, most often thought of as a device that totalizes input events, is the basic building block for all digital test and measurement applications. The digital counter has come a long way since it first appeared on the commercial marked. Even in its original form it was recognized as perhaps the most useful measuring instrument to emerge from the laboratory since the oscilloscope. The original application of the digital counter was that of a frequency counter.,机械工业出版社 http:/www.cmpbook.com,Passage One Digital Counter and Digital Frequency Counters,The main gate is nothing more than a logic AND circuit. When both the input conditioning and main-gate flip-flop are logically true, the main gate opens for a period of time that is determined by the timer base divider. While the main gate is open, the conditioned input signal pulses are passed through to the counting register, where they are tallied and then scaled for output by the display circuitry. At the end of the counting period, the main gate is closed and counter reset for the next sampling period.,机械工业出版社 http:/www.cmpbook.com,Passage One Digital Counter and Digital Frequency Counters,Digital Frequency Counter When the main gate is controlled by an accurate time interval, the counter is in the frequency mode. The frequency mode is similar to the totalize mode described above, with the difference being in the way the gate control is operated. For frequency measurements, the counting time interval is precisely controlled to be multiples of a second. If, for example, 45,500 pulses pass through to the counting register while the main gate remains open for one second, then the input signal frequency is 45.5 kHz. Depending on the number of digits in the read out, this number could be directly or expressed as powers of ten.,机械工业出版社 http:/www.cmpbook.com,Passage One Digital Counter and Digital Frequency Counters,To measure frequencies that would otherwise exceed the maximum count of the counting register, the time interval of the main gate can be reduced, with an appreciate change made to the scale factor. A similar number of pulses (45,500) accumulating in the counting register within a 0.1 second period, for example, would represent a frequency of 455 kHz; 25,000 pulses counter within 10s is 2.5MHz, and so forth. Scaling can be done automatically by the positioning of the decimal point on the digital read out, as the timer base period is switched from range to range.,机械工业出版社 http:/www.cmpbook.com,Passage One Digital Counter and Digital Frequency Counters,Instead of manually switching to the appropriate timer range, some instruments have an automatic range selection system called auto ranging. The ranger usually consists of a circuit that generates voltage level; one of several transistor switches is turned on to select the correct timer base and decimal point position. Using the frequency counter as a frequency meter, however, is exploiting but one of its several electronic counter functions. A counter can also indicate the period of an input signal, compare two signals in the ratio mode, indicate the time between two points on a waveform, or do reciprocal counting.,机械工业出版社 http:/www.cmpbook.com,Passage One Digital Counter and Digital Frequency Counters,Exercises . Match the items listed in the following two columns. 1. electronic digital counter a. 计数寄存器 2. main gate b. 频率计数器 3. counting register c. 采样周期 4. frequency counter d. 电子数字计数器 5. sampling period e. 主控门,机械工业出版社 http:/www.cmpbook.com,Passage One Digital Counter and Digital Frequency Counters,. Complete the following sentences according to the text. 1. is the basic building block for all digital test and measurement applications. 2. The main gate is a logic circuit. 3. While the main gate is open, the conditioned input signal pulses are passed through to the , where they are tallied and then scaled for output by . 4. To measure frequencies that would otherwise exceed the maximum count of , the time interval of the main gate can be reduced, with an appreciate change made to the scale factor.,机械工业出版社 http:/www.cmpbook.com,Class is over!,Have a rest!,追 求,机械工业出版社 http:/www.cmpbook.com,