Indicator on valve not giving signal - and some basic questions

Thread Starter

StrongPenguin

Joined Jun 9, 2018
287
We have these four valves onboard our ship, and some time ago one of them broke and was replaced with a new one. But the new valve does not send the open/closed signal to the remote.

I have been assigned to find out why and come with a (hopefully) solution. I have not open the valve box yet, so I have no idea what the problem is, so it could well just be a broken switch or wire, though I know two other guys have looked at it and found nothing. I thought I might as well as you guys some basic questions, regarding RF, because I have very little knowlege about the topic.

I assume it is RF, since it's a very simple system and the remote only has up/down and on/off buttons. And the four indicator LED's.

Here come the questions.

1) In order for the remote to know which one of the valves is open, do the transmitters need to send on different frequencies?

2) If I have a whole bunch of valves, say 100, is it possible that all could send on the same frequency and still know which one is doing what? Guess that would require a controller on the valve side, or maybe just a certain sequence?

3) Is it true, that UHF (I often confuse UHF/VHF) penetrates better than VHF, things like steel and concrete? And that UHF also is more sensitive to noise? We have a UHF in our engine control room, and that radio is basically useless because of noise.

4) What is noise on the radio, actually?

5) If I have two radios, would it be possible for both to talk at the same time, if the "click mute" function was not present?
 

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wayneh

Joined Sep 9, 2010
17,153
1) In order for the remote to know which one of the valves is open, do the transmitters need to send on different frequencies?
Not necessarily. They could send data along with a digital code that identifies the source. Like a garage door opener.
2) If I have a whole bunch of valves, say 100, is it possible that all could send on the same frequency and still know which one is doing what? Guess that would require a controller on the valve side, or maybe just a certain sequence?
As above, as long as they have unique codes, it can all work at the same frequency. Having 100 might require something more sophisticated than a garage-door type system. It may require something more like a network protocol to mediate the collisions that would happen otherwise occur.
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
287
Not necessarily. They could send data along with a digital code that identifies the source. Like a garage door opener.
As above, as long as they have unique codes, it can all work at the same frequency.
So it sends the RF signal simultaneously as the data? I've stared reading on RF transmission and the frequency band, but I find it difficult to wrap my head around the signals, or picture it in my head.
 

Yaakov

Joined Jan 27, 2019
3,492
Very basically, the radio transmitter is on a certain frequency and the receiver is tuned to that frequency. The signal from the transmitter is modulated which allows information to be sent to the receiver. The modulation scheme can be one of many things, in remote control FSK (Frequency Shift Keying) is very common.

with FSK 1’s and 0’s are sent by shifting the transmitter frequency up and down to specific values representing each. The receiver can then distinguish a one from a zero by the frequency it hears.

On top of this are different higher layers that frame the information with a preamble to allow synchronization, a length to allow the receiver to know how much to expect, and a checksum to determine that the message arrived intact.

Additionally, there are schemes to allow many transmitters to share a frequency in the time domain, that is, to let them take turns.

This is very basic and there are many details and variations to all of this.
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
287
@Yaakov I searched for the terms you mentioned, and looked at some pictures of FSK. It makes a bit more sense now, though I reckon there is a lot to be learnt.

I will probably have a look at the valve next week, and for good measure, write here if I find anything of interest.

Thanks for good explanations.
 

strantor

Joined Oct 3, 2010
5,633
Brand and model would be the first.
I know you're not TS but I'm asking because you have a background in shipping, is it normal for shipboard valves to be controlled by RF? I will be surprised if the answer is "yes." I would not trust radio-controlled-anything for critical systems, and it seems there are not a whole lot of systems on a ship that are not critical. Also it seems the metal tomb is not the optimal environment for radio. I would expect all electrically powered valves on a ship to be hard wired; power, plus control & feedback signals, all hard wired.
 

atferrari

Joined Jan 6, 2004
4,425
I know you're not TS but I'm asking because you have a background in shipping, is it normal for shipboard valves to be controlled by RF? I will be surprised if the answer is "yes." I would not trust radio-controlled-anything for critical systems, and it seems there are not a whole lot of systems on a ship that are not critical. Also it seems the metal tomb is not the optimal environment for radio. I would expect all electrically powered valves on a ship to be hard wired; power, plus control & feedback signals, all hard wired.
Not that I know, strantor. Never heard of one.

I vaguely recall valves with some capability to signal open / closed, used in ballast / cargo piping scheme in a tanker (LPG), but not RF.

I am trying to remember the valves in one of the (wave piercing) fast ferries in service down here. The whole data/control was referred to a pair of central panels in the ER. The model / brand of that system was ISIS (go figure).
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The brand that came to mind but I know it is not related directly was Danfos with 4-20ma circuitry.
 

Delta Prime

Joined Nov 15, 2019
1,149
Hello there :)
SCADA (Supervisory Control And Data Acquisition) systems monitor and control operations remotely.
Valve, solenoids, pumps. Uses UHF and VHF on board ships and in industrial facilities. Please confirm the use of SCADA data on your vessel and I may be able to help you.
 

Thread Starter

StrongPenguin

Joined Jun 9, 2018
287
@atferrari The captain has put the valves on the lowest priority, so I doubt I will have a look at them this trip. And the weather just got terrible, will stay so for a week. North Sea, always fun..

@strantor I've been a marine engineer for some years now, I have never encountered an RF valve on a critical system, though I have seen them on non critical systems, like this one. The controller is never more than a few meters away from the valve, with nothing blocking the way.

@Delta prime Never heard the term SCADA before, but our system is sorta built up like that one. We have Outstations, where signals from pumps, engines, valves etc., meet and are translated (some) then multiplexed into a power management computer, where we can start engines, close breakers, start pumps. But these valves is not on this system.

Hopefully I can open the box tomorrow, if the weather allows it. I am pretty curious now.
 
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