Thubika,
It's NOT about the number of wires in a multi-core cable--it's how the wires are arranged in the cables in order to reduce the possibility of electrical interference from other wires in the cable, and from other cables, as well.
A "1 pair cable" (to use your description), is most likely also known as a "twisted, shielded pair" cable (often referred to as a TSP cable). In this cable, the two cores are twisted around each other in such a way that the likelihood of induced voltages from nearby cores/cables are more difficult to happen. Further, these twisted cores are usually surrounded by a foil wrapping called the "shield," and there is also usually a bare wire ("core") called the "drain wire" that lays in with the twisted cores and contacts the foil wrapping. The purpose of this foil is to intercept and "capture" any electrical interference, and transmit it to the bare wire. The bare wire is to be grounded (earthed) at one end of the length of the twisted, shielded pair cable thereby "draining" any induced currents (from nearby cores/cables) to earth in one direction (to the single ground/earth connection).
A cable made up of multiple cores without any provision for protecting against electrical interference and induced currents from nearby cores/cables would not protect transmitter signals from being negatively impacted.
MANY people have tried what you are suggesting--a core is a core is a core is a means of transmitting current--for transmitters, and speed sensors, and all manner of low-voltage, low-current control and protection signals. Because, cables designed for such applications are more expensive and need to be properly installed (such as properly grounding/earthing the drain wire at one end of the cable). And, multi-core cables without twisting and shielding are much less expensive and don't require special terminations. And, they have been surprised at the results--VERY surprised, usually. Erratic measurements; unstable processes; nuisance shutdowns and trips which can't be easily troubleshot or explained or eliminated. UNTIL the proper type of cable is installed and properly terminated. And, then--VOILA!!! Suddenly, things seem to run a lot smoother and require less human attention (which is the aim of all automation).
This is a very simple explanation, and if you want more detail--it's certainly available by using your preferred World Wide Web search engine. As with everything technical, it can get VERY complicated and detailed VERY quickly--more-so than you ever thought possible or wanted to imagine.
Suffice it to say: Use the proper cables for the proper applications. And your life will be much simpler and easier.
[NOTE: Some multi-core cables do have a "shield" around untwisted conductors (cores). This is usually done to try to eliminate the amount of electrical interference produced by the current flowing in the cores in the cable--not to prevent electrical interference from affecting the cores in the cable. So, this type of multi-core cables is NOT suitable for transmitters and the like, even though it has "shielding."]
Hope this helps!
Thank you David_2 and CSA for the information and clarifications. Well appreciated!If a cable is carrying low-level analog signals, the shield drain wires should be grounded at only one end. Grounding at one end only prevents any current from flowing between none equipotential ground points, because ground current flowing in the drain wire or shield can couple into the small-signal wires and corrupt the signal. When the drain/shield is connected at only one end, it serves as a Farady cage to isolate the low level signal(s) from noise/interference.
David_2,Near lightning strike
David_2,Surge or lightning protection is a whole field in itself. The web site explains some basics of direct strike lightning protection and also mentions that 65% of voltage/current surges are locally produced by switching of electrical loads like motors or heating systems.
https://blog.nvent.com/erico-the-difference-between-lightning-protection-and-surge-protection/
For instrumentation, the commercially available surge protection devices can be a module that plugs-in to a DIN mounted wiring terminal block, so that the module can be replaced when the protection device's 'capacity' has been depleted. The big mystery is knowing when the protection is depleted so it can be replaced.
Phoenix Contact even offers an e-learning course on surge protection.
https://www.phoenixcontact.com/online/portal/ca?1dmy&urile=wcmath:/caen/web/main/products/technology_pages/subcategory_pages/Surge_protection_e-learning/8a58d320-4cc8-4c3a-8553-8279f411871e
Obd,
Um, ..., Er, ..., You didn't even acknowledge whether or not lightning strikes and/or electrical storms may actually exist in the area where this equipment is located.
Further, this query is not even really remotely related to the topic of the original poster.
You should be using twisted, shielded pairs for the connection between the Surge Protector and the Lidar (some 500 metres away). You could probably get away with just using two individual cores for the 24 VDC power supply, but for the RS-485 you need to be using twisted, shielded pair(s)--and the shield drain wire(s) of the pair(s) should be grounded at one end only, and by conventions the shield drain wires should be grounded where the power in the wire originates (so in the Control Panel). The ground should be connected firmly to either functional earth (so-called "control" earth) if it exists at the site, or to protective earth.
There is probably a ground wire for the radar level gauge housing which should be firmly grounded--to protective earth, most likely.
And this is whether--or not--there are electrical storms or lightning strikes in the area which may affect the instrument, cable trays, etc., which should all be firmly grounded to protective earth.
Next, you need to determine where the wires between the Control Room Panel and the radar level gauge are routed. If they are in conduits or cable trays or cable vaults (or something similar) with high voltage wires and cables (anything above 120 VAC, and anything which switches power on and off and that power is 1.0 A or more, especially for higher voltages (above approximately 220 VAC) the interconnecting wire between the Control Room Panel surge protector and the radar level gauge needs to be routed in a different manner and AWAY from the higher voltage/higher current wires (cores) and cables. EVEN IF THERE ARE NOT ELECTRICAL STORMS OR LIGHTNING IN THE AREA WHICH MAY STRIKE OR AFFECT THE EQUIPMENT (most specifically the radar level gauge, and/or the conduit/cable tray which the interconnecting wire is routed through).
MANY people, even some (alleged) technicians, but most usually supervisors and managers, do not want to spend the money required for proper signal level separation--keeping the low-voltage, low-current wires (cores) away from the higher voltage/higher current wires (cores). And, shielding and drain wires DO NOT REPLACE MAINTAINING PROPER SIGNAL LEVEL SEPARATION IN CONDUITS/CABLE TRAYS/CABLE VAULTS, etc. Full stop. Period.
It's possible you're fighting a combination of issues (it happens often)--incorrect shield drain wiring (terminated at both ends instead of just one), improper signal level separation from higher voltage/higher current wires and cables, and maybe even insufficient surge protection. In addition to improperly grounded equipment housing(s), and poor earthing grids. You have to consider it all.
And consider it a learning experience. "Good judgment comes from experience; experience comes from poor judgement." Truer words were never spoken--about technical issues, as well as everyday life. It's just the way it goes. You have to crack some eggs to make a souffle. You can't have your cake, and eat it, too. Into each life a little rain must fall (even in the desert--and when it does rain in the desert, isn't it beautiful--if only for a day or two!).
Best of luck. Please write back to let us know what you found and how you resolved it--at least for now. Another truism is: "The definition of insanity is doing the same--and expecting different results." (Though if a clown gets elected, a circus should be the expected result. Sorry; couldn't resist that.) You've tried something; it didn't work. Doing the same thing isn't going to solve he problem (it doesn't seem like it will, anyway). If you're going to site, you need to look at how it was installed and wired and what could possibly be causing the surge protection to get damaged so quickly. Wiring practices, including signal level separation, and ambient conditions (electrical storms and lightning strikes), and equipment grounding (at the radar level detector, and of the Control Room Panel, and of the shield drain wire(s) (presuming twisted, shielded pair cores were used)).
Again, please write back to let us know how you fare!
1. drain/shield grounding
CSA: . . . the shield drain wire(s) of the pair(s) should be grounded at one end only, and by conventions the shield drain wires should be grounded where the power in the wire originates (so in the Control Panel).
Your site: The Drain wire was terminated at both ends. It was terminated at the earth point on the terminal board of the Radar Gauge and also at the earth point of the Panel.
I advocate grounding the drain wire at one end only, preferably at the control panel end.
2. Two panels
Your site: 2 different Panels that were installed in the control room side by side
Are the radar level units supplying discrete signals to the annunciator or are they supplying analog signals that a logic analyzer in the annuciator panel uses to make the decisions on alarms?
David_2,
Thanks for your contribution. As for your question please, find answer below:
Are the radar level units supplying discrete signals to the annunciator or are they supplying analog signals that a logic analyzer in the annuciator panel uses to make the decisions on alarms?
My Answer: The Radar Level Gauge supply Relay Digital Outputs from RL1-RL4 contacts to the Alarm annuciator panel.
Expecting further clarifications please. Thank you