HIMA F35011 DCS工控模块备件
电缆屏蔽只能在电缆的一端接地。通常，最好将电缆屏蔽层接地，使其尽可能靠近噪声源。对于模拟输入模块，将噪声最大的一端接地（通常是现场设备端）。切断电缆模块端的屏蔽层，并用热缩管进行绝缘。对于模拟输出模块，在模块端接地。切断电缆装置端的屏蔽层，并用热缩管进行绝缘。最好尽量缩短剥线电缆引线的长度，以尽量减少暴露在噪声环境中的非屏蔽导体的长度。可以直接连接到模块端子，或通过中间接线板进行连接。本节中的图表显示了各种模拟输入和模拟输出装置的接线。2.6.4.10.1模拟输入模块的屏蔽通常，模拟输入电缆的屏蔽应在模拟源处接地。然而，如果合适，每个通道的接地连接（标有COM和GND）可用于连接模拟输入模块的屏蔽。模拟输入模块的COM端子连接到模块中的公共模拟电路。GND端子连接到背板（机架接地）。屏蔽可以连接到COM或GND。本节显示了模拟输入模块的四个屏蔽接地示例。PACSystems*RX3i系统手册第3节GFK-2314T 2019年9月安装55模拟输入屏蔽带端子板接地对于不平衡源，接地屏蔽应连接到源公共或源端接地。如果模块的所有电源输入来自同一位置且参考同一公共点，则所有屏蔽接地应连接到同一接地点。如果模拟输入模块和现场设备（模拟源）之间有一个额外的接线板，请使用下图所示的方法，使用接线板上的端子继续每个电缆屏蔽。每根电缆只有一端接地，即靠近现场设备（模拟源）的一端。屏蔽连接在图37中以红色（粗体）显示。模拟源连接至机架接地模拟输入模块外壳端子板机器或设备模拟源模拟源模拟电源图37：带端子板的模拟输入屏蔽接地PACSystems*RX3i系统手册第3节GFK-2314T 2019年9月安装56附录a：模拟输入屏蔽对公共连接的接地在某些应用中，通过在源端将源公共点连接在一起，然后仅在一个模块COM端子处将公共线连接到模块，可以改善噪声抑制。这将消除可能导致错误输入数据的多个接地或接地回路。图38中红色（粗体）显示了这里的常见连接。模拟源模拟输入模块COM模拟源模拟源模拟信号源图38：模拟输入屏蔽接地至公共连接PACSystems*RX3i系统手册第3节GFK-2314T 2019年9月安装57附录B：连接至模块端子板的模拟输入屏蔽通常最好在源端接地电缆屏蔽。如果这很困难，或者如果电气噪声不是问题，则可以在模拟输入模块端接地电缆屏蔽。
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.
