Wiring box with terminal panel using PCB circuit boards
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Six 24-core multi-core cables are used to connect to the DCS cabinet; for analog signals, whereas previously one analog signal (usually a 4-20mA signal) required a 2-core shielded cable, now one 24-core shielded cable can replace 12 such 2-core cables. This can save a lot of cables. If there are 2,400 analog signals coming out of the DCS cabinet, previously 2,400 two-core cables were required, but now only 200 24-core cables are needed. This reduces the amount of cable used and also decreases the space occupied by the cables in the cable trays. The junction boxes are placed in various corners of the workshop; it only takes a distance of ten to twenty meters for the wires to be connected to the instruments. If there is any increase or decrease, or shift in the instrument, simply change the wiring between the junction box and the instrument. Do not touch the cables between the DCS cabinet and the junction box. At worst, if there aren’t enough connection points, one can simply use multi-core cables and junction boxes. The junction box is a deep-type explosion-proof box; in the machinery industry, an ordinary box is sufficient. A terminal panel made of circuit boards is used – traditional electrical terminals take up a lot of space, while terminal panels made of circuit boards allow twice as many terminals to be installed in a limited space. Place the terminal panel in front of the box to make it easier for workers to connect the wires; the panel has a hole in the middle to allow cables to pass through and connect to the terminal connections on the panel. The terminal panel has 12 cut-off valve positions in a row; each cut-off valve is equipped with one DO output and two feedback signals: feedback indicating when it is in the open position and feedback indicating when it is in the closed position. The lower row of the panel contains 36 analog input points; it is possible to assign as many analog inputs or outputs as needed. The analog inputs can be powered by the DCS system or have their own power supply, with high-power mass flow meters being equipped with their own power sources. The instrument outputs active analog signals. On the left is the 6-channel 24V power supply, equipped with a fuse. In the case of a mass flow meter, 4 wires are used: 2 wires are connected to the 24V power supply, and 2 wires are connected to the analog input terminals. The image shows the 24-core terminal already connected
Multi-core cables + on-site junction boxes – it’s a proven technology! The wiring boxes in Area II of the site can use intrinsically safe types. If circuit boards are used, intrinsically safe designs may not meet explosion-proof requirements; switching to flameproof designs is costly (the image shows a flameproof design), and the signals need to be separated according to different type requirements. What is this used for, in PLC control?
It involves using 24-core wires to connect from the Zhejiang University DCS cabinet to the workshop. In the past, if 2400 wires were needed, just over 200 were sufficient; this results in a significant reduction in the amount of cable used. With fewer cables running along the cable trays, maintenance becomes easier, as well as the task of locating wires. It’s just a junction box, with no electrical appliances inside. It features analog input and output, with a maximum current of 26 MA; the short-circuit current for analog input is also 26 MA. The current for digital output is around 500 MA, while the current for digital input is a few milliamps. Additionally, it is equipped with a 24V power supply. Mine is of the flameproof type; for safety reasons, the factory uses flameproof designs. The advantage of mine is that it’s made with a PCB, which allows for more wiring terminals and makes wiring easier – with ordinary rail-type wiring terminals, it’s difficult to insert them in. The other option is to place the wires under the PCB, which keeps things very neat