單片機(jī)系統(tǒng)外文翻譯-單片機(jī)(文件)
【正文】 ife on the plant : we live at the bottom of an atmospheric ocean that extends upward for many miles . This mass of air has weight , and this weight pressing downward causes atmospheric pressure . Water , a fundamental necessity of life , is supplied to most of us under pressure . In the typical process plant , pressure influences boiling point temperatures , condensing point temperatures , process efficiency , costs , and other important factors . The measurement and control of pressure or lack of itvacuumin the typical process plant is critical. The working instruments in the plant usually include simple pressure gauges , precision recorders and indicators , and pneumatic and electronic pressure transmitters . A pressure transmitter makes a pressure measurement and generates either a pneumatic or electrical signal output that is proportional to the pressure being sensed . In the process plant , it is impractical to locate the control instruments out in the place near the process . It is also true that most measurements are not easily transmitted from some remote location . Pressure measurement is an exception , but if a high pressure of some dangerous chemical is to be indicated or recorded several hundred feet from the point of measurement , a hazard may be from the pressure or from the chemical carried. To eliminate this problem , a signal transmission system was developed . This system is usually either pneumatic or electrical . And control instruments in one location . This makes it practical for a minimum number of operators to run the plant efficiently . When a pneumatic transmission system is employed , the measurement signal is converted into pneumatic signal by the transmitter scaled from 0 to 100 percent of the measurement value . This transmitter is mounted close to the point of measurement in the process . The transmitter outputair pressure for a pneumatic transmitteris piped to the recording or control instrument . The standard output range for a pneumatic transmitter is 20 to 100kPa , which is almost universally used . When an electronic pressure transmitter is used , the pressure is converted to electrical signal that may be current or voltage . Its standard range is from 4 to 20mA DC for current signal or from 1 to 5V DC for voltage signal . Nowadays , another type of electrical signal , 5 kPamAkPamAkPakPa mAmAKr 420 ?????which is being mon , is the digital or discrete signal . The use of instruments and control systems based on puter or forcing increased use of this type of signal . Sometimes it is important for analysis to obtain the parameters that describe the sensor/transmitter behavior . The gain is fairly simple to obtain once the span is know . Consider an electronic pressure transmitter with a range of 0~600kPa . The gain is defined as the change in output divided by the change in input . In this case , the output is electrical signal (4~20mA DC) and the input is process pressure (0~600kPa) . Thus the gain . Beside we must measure Temperature Temperature measurement is important in industrial control , as direct indications of system or product state and as indirect indications of such factors as reaction rates , energy flow , turbine efficiency . and lubricant quality . Present temperature scales have been in use for about 200 years ,the earliest instrumen
高考資料相關(guān)推薦
鄂ICP備17016276號(hào)-1