Testing of electronic high level alarms

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hugerich
Tanktop Cleaner
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Testing of electronic high level alarms

Postby hugerich » Mon Oct 21, 2013 8:11 am

Hi all, first time posting here. I am a recently qualified 4th engineer, just coming to the end of my first contract. I have plenty of questions but since I am the only Brit onboard (everyone else is Filipino!) sometimes it is very hard to get answers. So hopefully you guys can help me out when the manual or Google search fails me.

One question that has been bugging me is bunker tank high level alarms, of the electronic (I'm assuming capacitance) type. Before bunkering we are supposed to check high level alarms, however everyone I have asked about these electronic alarms has either said they don't need testing or they don't know how to test them. On my cadetship I was on 2 British flagged ships which used the float switch type which were easy to test, but since then I have only come across electronic ones that nobody seems to want to test, or doesn't know how.

So, have any of you seen these alarms, and if so, how do you test they are functioning correctly? Thanks in advance.

dieselbike
Bilge Dweller
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Re: Testing of electronic high level alarms

Postby dieselbike » Tue Oct 22, 2013 9:53 pm

Hello

The only way to test capacitance level sensors is to have an actual level in the tank or consult the manufacture they will probaly have a away to test them. Or if it is a small capacitance probe at the top of the tank you can take it out and put it into a bucket of fluid and wait for the alarm. I am currently on a vessel with Waterpilot FMX167 Endress + Hauser http://www.ii.endress.com/#product/FMX167
level sensors. These have failed before and the only way to test on board is to physically remove them and attach a test adapter and apply a pressure and check calibraition from there.

I could maybe help you more if you could tell me the model of capacitance level sensor?

cheers

hugerich
Tanktop Cleaner
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Joined: Thu Sep 19, 2013 10:55 pm

Re: Testing of electronic high level alarms

Postby hugerich » Wed Oct 23, 2013 10:38 am

Hi,

Well another problem is that nobody seems to have a clue where the alarms are to begin with, but I'm sure with some investigation I will find them. I did spot one for one of the MDO storage tanks today while doing another job, marked as the 85% probe and side mounted so I guess I will find a similar arrangement in the HFO tanks, an 85% and another at 95%. When I get a chance I will pop the back off it and see what is there, perhaps there will be some instructions or the like. If there is nothing there then I guess taking the whole assembly out would be the only option! Thanks for your insight.

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JollyJack
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Re: Testing of electronic high level alarms

Postby JollyJack » Fri Oct 25, 2013 7:26 pm

Rule 1 for anything electronic on a ship is DO NOT TRUST IT

and NEVER, EVER, EVER trust an electronic level alarm, use a sounding tape, it will save you jail time and the ship huge pollution fines when the tank overflows. If you go by the electronic level alarm, that's what will happen, the tank will overflow.
Discourage incest, ban country "music".

hugerich
Tanktop Cleaner
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Re: Testing of electronic high level alarms

Postby hugerich » Sat Oct 26, 2013 9:21 am

Don't worry, I am well aware of the potential problems with electronics. Only this week I came down for the morning and saw one tank that read 150m3 the day before now reading zero, a few minutes of panic until I took a sounding and found it was all still there rather than in a big black streak behind us. The only reason I want to find these alarms is because our company checklist before bunkering specifies that the high level alarms must be tested, and I don't like putting my name to jobs that I haven't done.

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JollyJack
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Re: Testing of electronic high level alarms

Postby JollyJack » Sat Oct 26, 2013 7:29 pm

I have found that electronic gizmos are great for doing mindless, repetitive things very quickly, temporarily storing data, playing video games, and not much else. A computer is an incredibly stupid machine. In a stable, climate controlled environment (which is why they put control rooms on ships, the a/c is for the computers, not the Engineers), they can work for months with no problems. However, in a hot, humid, vibrating engine room thrown around at the whim of the sea, they can be about as much practical use as a screen door on a submarine. Just my experience, anyway.
Discourage incest, ban country "music".

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Big Pete
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Re: Testing of electronic high level alarms

Postby Big Pete » Mon Oct 28, 2013 12:00 am

Hi Hugerich,

Welcome to the site, it is very good to see someone like you who takes a keen interest and trys to understand how everything works and what it does.
I dont have much experience with these alarms and, if they are capacitance alarms the normal way to test them is by immersing them in liquid, as previously said.
However, the capacitance level sensors on oily water seperators work through a Wheatstone Bridge type electrical circuit and there is a potentiometer to adjust the set point. When you take the covers off you may be able to simulate an alarm by adjusting a potentiometer inside, however, before changing any settings mark the original position, so you can return the settings to original. This will however only prove that the electronic circuit works, not that the probes do! If they are encrusted in dirt, there may be no change in the capacitance they measure in air and when in oil (both are insulators anyway).
If there is an adjustment inside the level sensor unit, the best way to verify that the unit is working is probably to remove it, clean the electrodes and place it in the liquid it should be measuring the level of, and adjust the potentiometer until it alarms, then check that it does not alarm in air. Make sure the tank wont overflow out of the alarm port when you remove it!!
Good luck.

BP
It is always better to ask a stupid question than to do a stupid thing.

hugerich
Tanktop Cleaner
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Re: Testing of electronic high level alarms

Postby hugerich » Sun Nov 10, 2013 9:38 am

Well, I finally got round to taking a look at these. I took the back off one and there was a test button, and pressing it set the alarm off. I can only assume this bridges the contacts, so testing the circuit as mentioned rather than the actual probe. Haven't taken the actual probe out as we don't have any easily accessible suitable tanks for that right now, but at least I now know how to do my job properly. Thanks guys!


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