5X00070G01?EMERSON 數(shù)字量控制數(shù)字量控制實(shí)際的物理量，除了開(kāi)關(guān)量、模擬量，還有數(shù)字量。如機(jī)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(shù)。這是50年代誕生于美國(guó)的基于計(jì)算機(jī)的控制技術(shù)。當(dāng)今已很普及，并也很完善。目前，先進(jìn)國(guó)家的金屬切削機(jī)床，數(shù)控化的比率已超過(guò)40％～80％，有的甚至更高。 PLC也是基于計(jì)算機(jī)的技術(shù)，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(jì)數(shù)脈沖，頻率可高達(dá)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(dá)幾十k。有了這兩種功能，加上PLC有數(shù)據(jù)處理及運(yùn)算能力，若再配備相應(yīng)的傳感器（如旋轉(zhuǎn)編碼器）或脈沖伺服裝置（如環(huán)形分配器、功放、步進(jìn)電機(jī)），則完全可以依NC的原理實(shí)現(xiàn)種種控制。高、中檔的PLC，還開(kāi)發(fā)有NC單元，或運(yùn)動(dòng)單元，可實(shí)現(xiàn)點(diǎn)位控制。運(yùn)動(dòng)單元還可實(shí)現(xiàn)曲線插補(bǔ)，可控制曲線運(yùn)動(dòng)。所以，若PLC配置了這種單元，則完全可以用NC的辦法，進(jìn)行數(shù)字量的控制。新開(kāi)發(fā)的運(yùn)動(dòng)單元，甚至還發(fā)行了NC技術(shù)的編程語(yǔ)言，為更好地用PLC進(jìn)行數(shù)字控制提供了方便。用于數(shù)據(jù)采集隨著PLC技術(shù)的發(fā)展，其數(shù)據(jù)存儲(chǔ)區(qū)越來(lái)越大。如OMRON公司的PLC，前期產(chǎn)品C60P的DM區(qū)僅64個(gè)字，而后來(lái)的C60H達(dá)到1000個(gè)字；到了CQMI可多達(dá)6000個(gè)字。這樣龐大的數(shù)據(jù)存儲(chǔ)區(qū)，可以存儲(chǔ)大量數(shù)據(jù)

5X00070G01?EMERSON 數(shù)字量控制可以用計(jì)數(shù)器，累計(jì)記錄采集到脈沖數(shù)，并定時(shí)地轉(zhuǎn)存到DM區(qū)中去。 數(shù)據(jù)采集也可用A/D單元，當(dāng)模擬量轉(zhuǎn)換成數(shù)字量后，再定時(shí)地轉(zhuǎn)存到DM區(qū)中去。PLC還可配置上小型打印機(jī)，定期把DM區(qū)的數(shù)據(jù)打出來(lái)。PLC也可與計(jì)算機(jī)通訊，由計(jì)算機(jī)把DM區(qū)的數(shù)據(jù)讀出，并由計(jì)算機(jī)再對(duì)這些數(shù)據(jù)作處理。這時(shí)，PLC即成為計(jì)算機(jī)的數(shù)據(jù)終端。電業(yè)部門(mén)曾這么使用PLC，用以實(shí)時(shí)記錄用戶用電情況，以實(shí)現(xiàn)不同用電時(shí)間、不同計(jì)價(jià)收費(fèi)辦法，鼓勵(lì)用戶在用電低谷時(shí)多用電，達(dá)到合理用電與節(jié)約用電的目的。5用于進(jìn)行監(jiān)控PLC自檢信號(hào)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(shí)，完全可利用它進(jìn)行PLC自身工作的監(jiān)控，或?qū)刂茖?duì)象進(jìn)行監(jiān)控。這里介紹一種用PLC定時(shí)器作看門(mén)狗，對(duì)控制對(duì)象工作情況進(jìn)行監(jiān)控的思路。如用PLC控制某運(yùn)動(dòng)部件動(dòng)作，看施加控制后動(dòng)作進(jìn)行了沒(méi)有，可用看門(mén)狗辦法實(shí)現(xiàn)監(jiān)控。具體作法是在施加控制的同時(shí)，令看門(mén)狗定時(shí)器計(jì)時(shí)。如在規(guī)定的時(shí)間內(nèi)動(dòng)作完成，即定時(shí)器未超過(guò)警戒值的情況下，已收到動(dòng)作完成信號(hào)，則說(shuō)明控制對(duì)象工作正常，無(wú)需報(bào)警。若超時(shí)，說(shuō)明不正常，可作相應(yīng)處理。如果控制對(duì)象的各重要控制環(huán)節(jié)，都用這樣一些看門(mén)狗”看”著，那系統(tǒng)的工作將了如指掌，出現(xiàn)了問(wèn)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(duì)一個(gè)復(fù)雜的控制系統(tǒng)，特別是自動(dòng)控制系統(tǒng)，監(jiān)控以至進(jìn)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(jì)平均無(wú)故障運(yùn)行時(shí)間，降低故障修復(fù)時(shí)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.