闭路监控系统外文翻译(编辑修改稿)

闭路监控系统外文翻译(编辑修改稿)内容摘要：

corresponding “1” or “0”. In the analog inputs which have been converted to digital form, the patterns of ones and zeros in the internal representation will form binary numbers corresponding to the quantity being converted. Feedback Control The class of control problems to be examined here is one of considerable engineering interest. We shall consider systems with several inputs, some known as controls because they may be manipulated and others called external disturbances, which are quite unpredictable. For example, in an industrial furnace we may consider the fuel flow, the ambient temperature, and the loading of material into the furnace to be inputs. Of these, the fuel flow is accessible and can readily be controlled, while the latter two are usually unpredictable disturbances. In such situations, one aspect of the control problems is to determine how the controls should be manipulated so as to counteract the effects of the external disturbances on the state of the system. One possible approach to the solution of this problem is to use a continuous measurement of the disturbances, and from this and the known system equations to determine what the control inputs should be as functions of time to give appropriate control of the system state. Digital Interface Circuits The signals used within microputer circuits are almost always too small to be connected directly to the “outside world” and some kind of interface must be used to translate them to a more appropriate form. The design of section of interface circuits is one of the most important tasks facing the engineer wishing to apply microputers. We have seen that in microputers information is represented as discrete patterns of bits。 this digital form is most useful when the microputer is to be connected to equipment which can only be switched on or off, where each bit might represent the state of a switch or actuator. Care must be taken when connecting logic circuits to ensure that their logic levels and current ratings are patible. The output voltages produced by a logic circuit are normally specified in terms of worst case values when sourcing or sinking the maximum rated currents. Thus Voh is the guaranteed minimum “high” voltage when sourcing the maximum rated “high” output current Ioh, 5 while Vol is the guaranteed minimum “low” output voltage when sinking the maximum rated “low” output current Iol. There are corresponding specification for logic inputs which specify the minimum input voltage which will be recognized as a logic “high” state Vih, and the maximum input voltage which will be regarded as a logic “low” state Vil. For input interface, perhaps the main problem facing the designer is that of electrical noise. Small noises signals may cause the system to malfunction, while larger amounts of noise can permanently damage it. The designer must be aware of these dangers from the outset. There are many methods to protect interface circuits and microputer from various kinds of noise. Following are some example: 1. Input and output electrical isolation between the microputer system and external devices using an optoisolator or a transformer. 2. Removing high frequency noise pulses by a lowpass filter and Schmitttrigger. 3. Protecting against excessive input voltages using a pair of diodes to power supply reversibly biased in normal direction. For output interface, parameters Voh,Vol,Ioh and Iol of a logic device are usually much to low to allow loads to be connected directly, and in practice an external circuit must be connected to amplify the current and voltage to drive a load. Although several types of semiconductor devices are now available for controlling DC and AC powers up to many kilowatts, there are two basic ways in which a switch can be connected to a load to control it. With series connection, the switch allows current to flow through the load when closed, while with shunt connection closing the switch allows current to bypass the load. Both connections are useful in lowpower circuits, but only the series connection can be used in highpower circuits because of the power wasted in the series resistor R.. AT89C52 Compatible with MCS51™ Products， 8K Bytes of InSystem Reprogrammable Flash Memory， Endurance: 1,000 Write/Erase Cycles， Fully Static Operation: 0 Hz to 24 MHz，Threelevel Program Memory Lock， 256 x 8bit Internal RAM， 32 Programmable I/O Lines，Three 16bit Timer/Counters， Eight Interrupt Sources， Programmable Serial Channel Lowpower Idle and Powerdown Modes. Description The AT89C52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, three 16bit timer/counters, a sixvector twolevel interrupt architecture, a fullduplex serial port, onchip oscillator, and clock circuitry. In addition, the AT89C52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning. The Powerdown mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next。