Control cable or computer cable, hard wire or flexible wire, 1.0 or 1.5
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1. How to distinguish between control cable KVVP and computer cable DJYPVP when selecting them? For the engineering projects I have worked on, the common design practice is to use KVVP for digital signals and DJYPVP for analog signals ； The second option is to use KVVP for both digital and analog signals ； The third option is to use DJYPVP for everything ； There were no issues during use at the end, and everything functioned properly. 2. Some use hard wires while others use soft wires; it depends on the cable samples provided by the manufacturer, with soft wires being used in mobile devices. Logically, neither the instruments nor the DCS are mobile, so there should be no need to use flexible cables; yet in some projects, flexible cables are still used. I don’t know what the considerations are. 3. Regarding the thread count, I have used both 1.0 and 1.5, and neither has caused any problems. Please share your thoughts on these three issues regarding how to make a choice, and whether there are any standard criteria that can be referred to.
The difference between the two types of cables lies in their shielding layers. For analog signals, double shielding is considered more reliable, and the advantages become apparent over longer distances. A cable with a 1.0 specification is sufficient for this purpose; I have used network cables to transmit 4-20mA signals over a distance of 250 meters without any issues. Therefore, if strength isn’t a concern, a 1.0 specification cable will do. Personally, I prefer rigid cables, as flexible cables require soldered terminals, which adds extra complexity
We generally use KVVP for digital signals and DJYVPR for analog signals; the standard voltage is 1.5. Personally, I think flexible cables are more convenient when it comes to cable installation, but they aren’t as easy to connect as rigid cables
1. Continuously varying analog signals are transmitted using twisted pairs. Because the interference magnetic fields generated by the two wires can cancel each other out, this prevents induced currents from building up on the opposing conductors and affecting the current readings. For the DI signal, although the 0/1 indicator is a voltage value, it is essentially driven by a threshold current; therefore, KVV can be used. The DO signal is generally provided with a source output; it essentially serves to power the device (it’s not a “signal”), and twisted pairs are not necessary. Since the level of interference is related to the length of the cable, KVV can indeed be used for short circuits (within 100 meters or so). However, one thing must be ensured: the instrumentation cable must have overall shielding to eliminate interference from external electromagnetic fields, especially those cables that lead to the MCC. 2. Type 2 conductors (7-strand stranded conductors) are commonly used, as the wiring compartments of metering equipment are small; moreover, small trunking channels are required inside the terminal cabinets, which necessitates a certain degree of flexibility in the wires to facilitate wiring. 3. AI/AO/DI: The current is very low; 1.0 allows a distance of around 7/8 hundred meters. DO is a powered output, and the conductor cross-sectional area depends on the power of the load. Both HG and SH have specifications, but they only state what \"should\", \"is advisable\", or \"can be done\", without explaining the reasons – this is a characteristic of Chinese specifications.
Question: For the PNP position feedback of valves, should a multi-core control cable be used or a split-screen computer cable?
The feedback signal from the valve position switch is not an instrument signal
DJYVP can be used for straight pull cables, while DJYPVP is used for multi-core cables. However, computer cables are a bit more expensive than control cables, and they are available from both hard and soft cable manufacturers. For pull-down applications, a cross-sectional area of 1.5 or more is generally used, while for multi-core types, 1.0 or more is required.
Either one is fine; there’s no difference. For factories that are a few hundred meters away, a value of 1.0 is sufficient for low-power instruments; for instruments with higher power consumption (such as mass flow meters, gas sensors, and alarms), a value of 1.5 is needed.