【導(dǎo)讀】畢業(yè)設(shè)計（論文）。題目基于PLC的電鍍生產(chǎn)線監(jiān)控系統(tǒng)設(shè)計。系（部）電氣工程與自動化系。專業(yè)電氣自動化技術(shù)。本設(shè)計通過如何利用德國西門子PLCS7-200進(jìn)行自動化電鍍生產(chǎn)線控。制，在本次設(shè)計中，我們從自動控制技術(shù)器件在國內(nèi)的應(yīng)用前景及電鍍生產(chǎn)。線生產(chǎn)現(xiàn)場的環(huán)境來考慮，以使該生產(chǎn)線真正具備自動生產(chǎn)運行為目的，從。而采用在當(dāng)前及以后都應(yīng)用廣泛且能適應(yīng)多種環(huán)境的可編程控制器來控制。整個工作流程的方案。重點分析了系統(tǒng)軟硬件設(shè)計部分，并給出了系統(tǒng)硬件。接線圖、PLC控制I/O端口分配表以及整體程序流程圖等，實現(xiàn)了電鍍生產(chǎn)。自動化，提高了生產(chǎn)效率，降低了勞動強度，大大提高了工作人員的工作環(huán)。為適應(yīng)現(xiàn)代傳統(tǒng)的工業(yè)控制系統(tǒng)，還采用了基于組態(tài)王軟件的系統(tǒng)。作為上位機，配合下位機PLC完成了該系統(tǒng)的實時監(jiān)控系統(tǒng)功能，更好的使

　　

【正文】 s are shown as two lines, and will be open (nonconducting) when the input is not energized. Normally closed contacts are shown with two lines with a diagonal line through them. When the input coil is not energized the normally closed contacts will be closed (conducting). Relays are used to let one power source close a switch for another (often high current) power source, while keeping them isolated. A n example of a relay in a simple control application is shown in Figure . In this system the first relay on the left is used as normally closed, and will allow current to flow until a voltage is applied to the input A. The second relay is normally open and will not allow current to flow until a voltage is applied to the input B. If current is flowing through the first two relays then current will flow through the coil in the third relay, and close the switch for output C. This can be read logically as C will be on if A is off and B is on. PROGRAM The first PLC were programmed with a technique that was based on relay logic wiring schematics. This eliminated the need to teach the electricians, technicians and engineers how to program a puter but, this method has stuck and it is the most mon technique for programming PLC today. To interpret this diagram imagines that the power is on the vertical line on the left hand side, we call this the hot rail. On the right hand side is the neutral rail. In the figure there are two rungs, and on each rung there are binations of inputs (two vertical lines) and outputs (circles). If the inputs are opened or closed in the right bination the power can flow from the hot rail, through the inputs, to power the outputs, and finally to the neutral rail. An input can e from a sensor, switch, or any other type of sensor. An output will be some device outside the PLC that is switched on or off, such as lights or motors. In the top rung the contacts are normally open and normally closed, which means if input A is on and input B is off, then power will flow through the output and activate it. On the left most part of the rung, power could flow 洛陽理工學(xué)院畢業(yè)設(shè)計（論文） 34 through the top if C is off and D is on. Power could also (and simultane ously) flow through the bottom if both E and F are true. This would get power half way across the rung, and then if G or H is true the power will be delivered to output Y. In later chapters we will examine how to interpret and construct these diagrams. There are other methods for programming PLC. One of the earliest techniques involved mnemonic AND statement recalls the last two numbers remembered and if the y are both true the result is a 1。 otherwise the result is a 0. This result now replaces the two numbers that were recalled, and there is only one number remembered. The process is repeated for lines 00003 and 00004, but when these are done there are now three numbers remembered. The oldest number is from the AND, the newer numbers are fr om the two LD instructions. The AND in line 00005 bines the results from the last LD instructions and now there are two numbers remembered. The OR instruction takes the two numbers now remaining and if either one is a 1 the result is a 1, otherwise the result is a 0. The last instruction is the ST (store output) that will look at the last value stored and if it is 1, the output will be turned on。 if it is 0 the output will be turned off. Even if you have programmed a PLC with ladder logic, it will be converted to mnemonic form before being used by the PLC. In the past mnemonic programming was the most mon, but now it is unmon for users to even see mnemonic programs. Structured Text programming has been developed as a more modern programming language. It is quite similar to languages such as BASIC. PLC CONNECTIONS When a process is controlled by a PLC it uses inputs from sensors to make decisions and update outputs to drive actuators, as shown in Figure . The process is a real process that will change over time. Actuators will drive the system to new states (or modes of operation). This means that the controller is limited by the sensors available, if an input is not available, the controller will have no way to detect a condition. The control loop is a continuous cycle of the PLC reading inputs, solving the ladder logic, and then changing the outputs. Like any puter this does not happen instantly. Figure shows the basic operation cycle of a PLC. When 洛陽理工學(xué)院畢業(yè)設(shè)計（論文） 35 power is turned on initially the PLC does a quick sanity check to ensure that the hardware is working properly. If there is a problem the PLC will halt and indicate there is an error. For example, if the PLC backup battery is low and power was lost, the memory will be corrupt and this will r esult in a fault. If the PLC passes the sanity checks it will then scan (read) all the inputs. After the inputs values are stored in memory the ladder logic will be scanned (solved) using the stored values not the current values. This is done to prevent logic problems when inputs change during the ladder logic scan. After this the syste m goes back to do a sanity check, and the loop continues indefinitely. Unlike normal puters, the entire program will be run every scan. Typical times for each of the stages are in the order of milliseconds. Questions Should Pay Attention to When PLC Is in the Use PLC which should pay attention to in the application is specially the control device which serves for the industrial production, usually does not need to take any measure, may use directly in the industry environment. But, when the production environment is too bad, the electromagic interference is special intense, or installs uses improper, cannot guar