5X00070G01?EMERSON 數(shù)字量控制數(shù)字量控制實際的物理量，除了開關量、模擬量，還有數(shù)字量。如機床部件的位移，常以數(shù)字量表示。
數(shù)字量的控制，有效的辦法是NC，即數(shù)字控制技術。這是50年代誕生于美國的基于計算機的控制技術。當今已很普及，并也很完善。目前，先進國家的金屬切削機床，數(shù)控化的比率已超過40％～80％，有的甚至更高。 PLC也是基于計算機的技術，并日益完善。故它也完全可以用于數(shù)字量控制。PLC可接收計數(shù)脈沖，頻率可高達幾k到幾十k赫茲?？捎枚喾N方式接收這脈沖，還可多路接收。有的PLC還有脈沖輸出功能，脈沖頻率也可達幾十k。有了這兩種功能，加上PLC有數(shù)據(jù)處理及運算能力，若再配備相應的傳感器（如旋轉編碼器）或脈沖伺服裝置（如環(huán)形分配器、功放、步進電機），則完全可以依NC的原理實現(xiàn)種種控制。高、中檔的PLC，還開發(fā)有NC單元，或運動單元，可實現(xiàn)點位控制。運動單元還可實現(xiàn)曲線插補，可控制曲線運動。所以，若PLC配置了這種單元，則完全可以用NC的辦法，進行數(shù)字量的控制。新開發(fā)的運動單元，甚至還發(fā)行了NC技術的編程語言，為更好地用PLC進行數(shù)字控制提供了方便。用于數(shù)據(jù)采集隨著PLC技術的發(fā)展，其數(shù)據(jù)存儲區(qū)越來越大。如OMRON公司的PLC，前期產(chǎn)品C60P的DM區(qū)僅64個字，而后來的C60H達到1000個字；到了CQMI可多達6000個字。這樣龐大的數(shù)據(jù)存儲區(qū)，可以存儲大量數(shù)據(jù)

5X00070G01?EMERSON 數(shù)字量控制可以用計數(shù)器，累計記錄采集到脈沖數(shù)，并定時地轉存到DM區(qū)中去。 數(shù)據(jù)采集也可用A/D單元，當模擬量轉換成數(shù)字量后，再定時地轉存到DM區(qū)中去。PLC還可配置上小型打印機，定期把DM區(qū)的數(shù)據(jù)打出來。PLC也可與計算機通訊，由計算機把DM區(qū)的數(shù)據(jù)讀出，并由計算機再對這些數(shù)據(jù)作處理。這時，PLC即成為計算機的數(shù)據(jù)終端。電業(yè)部門曾這么使用PLC，用以實時記錄用戶用電情況，以實現(xiàn)不同用電時間、不同計價收費辦法，鼓勵用戶在用電低谷時多用電，達到合理用電與節(jié)約用電的目的。5用于進行監(jiān)控PLC自檢信號很多，內(nèi)部器件也很多，多數(shù)使用者未充分發(fā)揮其作用。
5X00070G01?EMERSON 數(shù)字量控制其實，完全可利用它進行PLC自身工作的監(jiān)控，或?qū)刂茖ο筮M行監(jiān)控。這里介紹一種用PLC定時器作看門狗，對控制對象工作情況進行監(jiān)控的思路。如用PLC控制某運動部件動作，看施加控制后動作進行了沒有，可用看門狗辦法實現(xiàn)監(jiān)控。具體作法是在施加控制的同時，令看門狗定時器計時。如在規(guī)定的時間內(nèi)動作完成，即定時器未超過警戒值的情況下，已收到動作完成信號，則說明控制對象工作正常，無需報警。若超時，說明不正常，可作相應處理。如果控制對象的各重要控制環(huán)節(jié)，都用這樣一些看門狗”看”著，那系統(tǒng)的工作將了如指掌，出現(xiàn)了問題，卡在什么環(huán)節(jié)上也很好查找。還有其它一些監(jiān)控工作可做。對一個復雜的控制系統(tǒng)，特別是自動控制系統(tǒng)，監(jiān)控以至進一步能自診斷是非常必要的。它可減少系統(tǒng)的故障，出了故障也好查找，可提高累計平均無故障運行時間，降低故障修復時間，提高系統(tǒng)的可靠性。

5X00070G01 EMERSON Digital quantity control Digital quantity control of actual physical quantities, in addition to switching quantities, analog quantities, and digital quantities. For example, the displacement of machine tool components is often expressed in digital quantities.
The effective way to control digital quantity is NC, that is, digital control technology. This is a computer-based control technology that was born in the United States in the 1950s. Today it is very popular and very well developed. At present, the ratio of metal cutting machine tools in advanced countries has exceeded 40% to 80%, and some even higher. PLC is also based on computer technology, and increasingly perfect. Therefore, it can also be used for digital quantity control. The PLC can receive counting pulses at frequencies as high as a few k to tens of k Hertz. The pulse can be received in a variety of ways, and can be received in multiple ways. Some PLC also has pulse output function, pulse frequency can also reach tens of k. With these two functions, coupled with PLC data processing and computing capabilities, if equipped with the corresponding sensor (such as rotary encoder) or pulse servo device (such as ring distributor, power amplifier, stepper motor), you can completely achieve various controls according to the principle of NC. High and mid-range PLC, also developed NC unit, or motion unit, can achieve point control. The motion unit can also realize curve interpolation and control curve motion. Therefore, if the PLC is configured with this unit, it can completely use the NC method to control the digital quantity. The newly developed motion unit, and even the NC technology programming language has been issued, which provides convenience for better digital control with PLC. With the development of PLC technology, its data storage area is getting larger and larger. For example, the PLC of OMRON company, the DM area of the early product C60P is only 64 words, and the later C60H reaches 1000 words; To CQMI can be up to 6000 words. Such a large data storage area can store a large amount of data.
5X00070G01 EMERSON Digital quantity control can use a counter to accumulate the number of pulses collected and periodically transferred to the DM area. Data acquisition can also be used as A/D unit, when the analog amount is converted to digital amount, and then periodically transferred to the DM area. The PLC can also be configured with a small printer to regularly type out the data in the DM area. PLC can also communicate with the computer, the data in the DM area is read out by the computer, and the data is processed by the computer. At this time, the PLC becomes the data terminal of the computer. The electricity industry has used PLC to record the user’s electricity consumption in real time, so as to achieve different electricity consumption time, different pricing and charging methods, and encourage users to use more electricity when the electricity is low, so as to achieve the purpose of reasonable electricity consumption and saving electricity. There are many PLC self-test signals for monitoring, and many internal devices, and most users do not give full play to their role.
5X00070G01 EMERSON Digital quantity control In fact, it can be fully used to monitor the PLC’s own work, or to monitor the control object. This paper introduces the idea of using PLC timer as a watchdog to monitor the work of the control object. If the PLC is used to control the action of a moving part, see whether the action is carried out after the control is applied, the watchdog method can be used to achieve monitoring. This is done by using a watchdog timer while exerting control. If the action is completed within the specified time, that is, the timer does not exceed the alarm value, and the action completion signal has been received, it indicates that the control object works normally and there is no need to alarm. If the timeout occurs, it indicates that the fault is abnormal and you can handle it accordingly. If each important control link of the control object uses such a watchdog to “see”, the work of the system will be well understood, and if there is a problem, it is also very good to find what link is stuck in. There are other monitoring tasks that can be done. For a complex control system, especially an automatic control system, it is necessary to monitor and further self-diagnose. It can reduce the system failure, fault can be found, can improve the cumulative average trouble-free running time, reduce the fault repair time, improve the reliability of the system.