HIMA F35011 DCS工控模塊備件
電纜屏蔽只能在電纜的一端接地。通常，最好將電纜屏蔽層接地，使其盡可能靠近噪聲源。對于模擬輸入模塊，將噪聲最大的一端接地（通常是現(xiàn)場設備端）。切斷電纜模塊端的屏蔽層，并用熱縮管進行絕緣。對于模擬輸出模塊，在模塊端接地。切斷電纜裝置端的屏蔽層，并用熱縮管進行絕緣。最好盡量縮短剝線電纜引線的長度，以盡量減少暴露在噪聲環(huán)境中的非屏蔽導體的長度?？梢灾苯舆B接到模塊端子，或通過中間接線板進行連接。本節(jié)中的圖表顯示了各種模擬輸入和模擬輸出裝置的接線。2.6.4.10.1模擬輸入模塊的屏蔽通常，模擬輸入電纜的屏蔽應在模擬源處接地。然而，如果合適，每個通道的接地連接（標有COM和GND）可用于連接模擬輸入模塊的屏蔽。模擬輸入模塊的COM端子連接到模塊中的公共模擬電路。GND端子連接到背板（機架接地）。屏蔽可以連接到COM或GND。本節(jié)顯示了模擬輸入模塊的四個屏蔽接地示例。PACSystems*RX3i系統(tǒng)手冊第3節(jié)GFK-2314T 2019年9月安裝55模擬輸入屏蔽帶端子板接地對于不平衡源，接地屏蔽應連接到源公共或源端接地。如果模塊的所有電源輸入來自同一位置且參考同一公共點，則所有屏蔽接地應連接到同一接地點。如果模擬輸入模塊和現(xiàn)場設備（模擬源）之間有一個額外的接線板，請使用下圖所示的方法，使用接線板上的端子繼續(xù)每個電纜屏蔽。每根電纜只有一端接地，即靠近現(xiàn)場設備（模擬源）的一端。屏蔽連接在圖37中以紅色（粗體）顯示。模擬源連接至機架接地模擬輸入模塊外殼端子板機器或設備模擬源模擬源模擬電源圖37：帶端子板的模擬輸入屏蔽接地PACSystems*RX3i系統(tǒng)手冊第3節(jié)GFK-2314T 2019年9月安裝56附錄a：模擬輸入屏蔽對公共連接的接地在某些應用中，通過在源端將源公共點連接在一起，然后僅在一個模塊COM端子處將公共線連接到模塊，可以改善噪聲抑制。這將消除可能導致錯誤輸入數(shù)據(jù)的多個接地或接地回路。圖38中紅色（粗體）顯示了這里的常見連接。模擬源模擬輸入模塊COM模擬源模擬源模擬信號源圖38：模擬輸入屏蔽接地至公共連接PACSystems*RX3i系統(tǒng)手冊第3節(jié)GFK-2314T 2019年9月安裝57附錄B：連接至模塊端子板的模擬輸入屏蔽通常最好在源端接地電纜屏蔽。如果這很困難，或者如果電氣噪聲不是問題，則可以在模擬輸入模塊端接地電纜屏蔽。
suppression, the cable shield should only be grounded at one end of the cable. It is generally best to ground the cable shield as close to the source of the noise as possible. For Analog Input modules, ground the end that is in the noisiest environment (usually the field device end). Cut the shield off at the module end of cable and insulate with shrink tubing. For Analog Output modules, ground at the module end. Cut the shield off at device end of cable and insulate with shrink tubing. It is best to keep the length of stripped cable leads as short as possible to minimize the length of unshielded conductors exposed to the noisy environment. Connections can be made directly to the module terminals, or via an intermediate terminal block. The diagrams in this section show wiring for various types of analog input and analog output installations. 2.6.4.10.1 Shielding for Analog Input Modules Generally, the shield for analog input cables should be grounded at the analog source. However, ground connections for each channel, labeled COM and GND, can be used to connect shields at the analog input module if appropriate. The COM terminals of the analog input module connect to the analog circuit common in the module. The GND terminals connect to the backplane (frame ground). Shields may be connected to either COM or GND. This section shows four shield grounding examples for analog input modules. PACSystems* RX3i System Manual Section 3 GFK-2314T Sept. 2019 Installation 55 Analog Input Shield Grounding with a Terminal Strip For an unbalanced source, the ground shield should be connected to the source common or ground at the source end. If all source inputs to the module come from the same location and are referenced to the same common, all shield grounds should be connected to the same ground point. If there is an additional terminal strip between the analog input module and the field devices (analog sources), use the method displayed in the following figure to continue each cable shield using a terminal on the terminal strip. Each cable is only grounded at one end - the end closer to the field devices (analog sources). Shield connections are shown in red (bold) in Figure 37. Analog Source Connection to Frame Ground Analog Input Module Enclosure Terminal Strip Machine or Equipment Analog Source Analog Source Analog Source Figure 37: Analog Input Shield Grounding with a Terminal Strip PACSystems* RX3i System Manual Section 3 GFK-2314T Sept. 2019 Installation 56 Appendix A: Analog Input Shield Grounding to Common Connections In some applications, noise rejection can be improved by connecting the source common points together at the source end, then connecting a common line to the module at only one module COM terminal. That will eliminate multiple grounding or ground loops that could cause false input data. The common connections here are shown in red (bold) in Figure 38. Analog Source Analog Input Module COM Analog Source Analog Source Analog Source Figure 38: Analog Input Shield Grounding to Common Connections PACSystems* RX3i System Manual Section 3 GFK-2314T Sept. 2019 Installation 57 Appendix B: Analog Input Shields Connected to Module Terminal Board It is usually preferable to ground cable shields at the source end. If that is difficult, or if electrical noise is not a concern, it may be acceptable to ground cable shields at the analog input module end.
