【正文】 s LG and FG terminals (LG : Line Ground, FG : Frame Ground) with the thickest and shortest wire possible. (The wire length must be 30 cm ( inch) or shorter.) The LG and FG terminals function is to pass the noise generated in the PLC system to the ground, so an impedance that is as low as possible must be ensured. As the wires are used to relieve the noise, the wire itself carries a large noise content and thus short wiring means that the wire is prevented from acting as an antenna. (b) The earth wire led from the earthing point must be twisted with the power supply twisting with the earthing wire,noise flowing from the power 西安石油大學本科畢業(yè)設計 （論文） supply wires can be relieved to the ,if a filter is installed on the power supply wires,the wires and the earthing wire may not need to be twisted. [Cables] The cables extracted from the control panel contain a high frequency noise the outside of the control panel, therefore, they serve as antennas to emit prevent noise emission,use shielded cable for the cables which are connected to the I/O modules and intelligent function modules and may be extracted to the outside of the control panel. The use of a shielded cable also increases noise resistance. The signal lines connected to the PLC I/O modules and intelligent function modules use shielded cables to assure noise resistance under the conditions where the shield is earthed. If a shielded cable is not used or not earthed correctly, the noise resistance will not meet the specified the shield of a shielded cable is earthed to the cabi bod y,please ensure that the shield contact with the body is over a large surface the cabi body is painted it will be necessary to remove paint from the contact fastenings must be metallic and the shield and earthing contact must be made over the largest available surface area. If the contact surfaces are too uneven for optimal contact to be made either use washers to correct for surface inconsistencies or use an abrasive to level the surfaces. The following diagrams show examples of how to provide good surface contact of shield earthing by use of a cable clamp. (1) Earthing of shielded of shield cable (a) Earth the shield of the shielded cable as near the module as possible taking care so that the earthed cables are not induced electromagically by the cable to be earthed. (b) Take an appropriate measures so that the shield section of the shielded cable from which the outer cover was partly removed for exposure is earthed to the control panel on an increased contact clamp may also be used as shown in the figure this case,however,apply a cover to the painted inner wall surface of the control panel which es in contact with the clamp. Note) The method of earthing by soldering a wire onto the shield section of the shielded 西安石油大學本科畢業(yè)設計 （論文） cable as shown below is not high frequency impedance will increase and the shield will be ineffective. (2) MELSECNET/H module Always use a doubleshielded coaxial cable (MITSUBISHI CABLE INDUSTRIES,LTD.:5C2VCCY) for the coaxial cables MELSECNET/H module. Radiated noise in the range of 30MHz or higher can be suppressed by use of the doubleshielded coaxial the doubleshielded coaxial cable by connecting its outer shield to the ground. Refer to (3) for the earthing of the shield. (3) Ether module, Web server module Precautions for using AUI cables, twisted pair cables and coaxial cables are described below. (a) Always earth the AUI cables connected to the 10BASE5 connectors. Because the AUI cable is of the shielded type,strip part of the outer cover and earth the exposed shield section to the ground on the widest contact surface as shown below. Refer to (4) for the earthing of the shield. (b) Use shielded twisted pair cables as the twisted pair cables connected to the 10BASET/100BASETX the shielded twisted pair cables,strip part of the outer cover and earth the exposed shield section to the ground on the widest contact surface as shown below. 西安石油大學本科畢業(yè)設計 （論文） Refer to (5) for the earthing of the shield. (c) Always use doubleshielded coaxial cables as the coaxial cables connected to the 10BASE2 connectors. Earth the doubleshielded coaxial cable by connecting its outer shield to the ground. Refer to (6) for the earthing of the shield. (4) I/O signal lines and other munication cables For the I/O signal lines and other munication cables lines (RS232,RS422, CCLink,etc.),if extracted to the outside of the control panel, also ensure to earth the shield section of these lines and cables in the same manner as in item (1) above. The Mitsubishi generalpurpose programmable logic controller has been designed and manufactured for applications in general industries, etc. Thus, applications i。s rated voltage and the terminal layout. Connecting a power supply that is different from the rating or incorrectly wiring the product could result in fire or damage. TROUBLESHOOTING When a module fails, you can change it without stopping the system. Online module change applies to the Q series I/O modules and to the A/D converter, D/A 西安石油大學本科畢業(yè)設計 （論文） converter, thermocouple input and temperature control modules of function version C and later. In order to increase the reliability of the system, not only highly reliable devices are used but also the speedy startup of the system after the occurrence of trouble bees an important start up the system speedily, the cause of the trouble must be located and eliminated correctly. The basic three points that must be followed in the troubleshooting are as follows. (1) Visual inspection Visually check the following. 1) Movement of sequencer (stopped condition, operating condition) 2) Power supply on/off 3) Status of input/output devices 4) Power supply module, CPU module,I/Omodule