PC based computer on a ship - Page 1
Forum section: electronics / general

author: Alana
author_rank: Frequent Contributor
timestamp: April 25, 2013, 05:14:15 pm
content: Are there any special considerations for PC type computer that would be on a sea ship?One of my bosses wants to sent one or 2 computers to several ships he is technical agent for. Those will not be mission critical but we want to make them as reliable as possible under conditions that they may end up. But we also want to be able to buy typical parts so that ship's electrician could buy a spare in any PC shop in ports those ships will visit.Computers will be placed for example on ship's bridge or chief engeneer office [anyway - inside] and will be connected to power grid and local network for internet access.What should i take under consideration choosing components for such machine except things i usually think of like what programs will be running?I'm thinking of SSD because this will be vibration proof. And of course brand name components.

author: ddavidebor
author_rank: Super Contributor
timestamp: April 25, 2013, 05:58:39 pm
content: You should do a sealed fanless computer.Sea air destroy electronic.

author: SeanB
author_rank: Super Contributor
timestamp: April 25, 2013, 06:06:17 pm
content: Whatever you get put it in an IP68 enclosure, with a heater and a desiccator pack of around 2kg for the motherboard and HDD. Place a set of IP68 rated connectors for video, USB and power and other IO to the cabinet, so that it always operates sealed. Use a chassis intrusion switch and connect it to the motherboard and monitor it. Power supply can go in there as well, so it will be a little bigger than a standard rack mount unit. The display, keyboards and mice/touchpads can be connected to standard connectors outside the case, just keep a spare interface cable around to replace them if they fail due to salt corrosion.Power supply wise, place a line conditioner before the power supply, and a UPS in another IP68 enclosure will not go amiss, with a separate vented battery enclosure with deep discharge recreational batteries inside. Pack along a set of spare monitors, keyboards and mice, and if you have a printer at least 5 cartridges in sealed packaging, and paper to use them up, so about 4 boxes of paper ( 10 000 sheets or so) and you are probably covered.Can be expensive, so just buy a whole load of Panasonic toughbooks and kingston locks to chain them down.

author: Alana
author_rank: Frequent Contributor
timestamp: April 25, 2013, 06:42:53 pm
content: Did i understood it correctly:- standard PC parts go into custom build case with IP68 protection rating- parts are mounted in the middle and all connectors are extended to IP68 rated connectors on side of this case [no build in connectors visible from the outside]- typical monitor/keyboard/mice are used but we send few spares- power quality on a cargo ship may be poor so on-line ups is recommended- additional protection against water = dessicant and heaterQuestions:- how reliable can be typical PC without those extra means of protection in such environment?- what about heat from PC components? I'm putting ATX PSU and CPU/motherboard in closed box without any ventilation holes.- what range of costs should i be aware of for such setups?- are there any regulations, standards, certificates i have to obey if we decide to make such case ourselves? I remind - this is not mission critical, just a PC for keeping spare parts inventory.

author: Jon Chandler
author_rank: Frequent Contributor
timestamp: April 25, 2013, 06:44:15 pm
content: Having installed, used and maintained software installations on navy ships, container ships and oil tankers, I can assure you that a standard PC will work fine. Air conditioning systems maintain normal humidity and temperature conditions in crew spaces and vibration levels are low enough not to be a problem.The only good advice so far is to use a UPS to provide a degree of protection against power interruptions.If you're talking about smaller ships, like fishing boats, environmental concerns would be more important.

author: SeanB
author_rank: Super Contributor
timestamp: April 25, 2013, 07:33:17 pm
content: IP68 is used where there is a chance of salt spray- like on the bridge, where you can have weather ingress. If oyu are using deeper inside the ship just use a few ruggedised notebooks or laptops ( or a few touch screen POS computers) as there you get the whole UI and a small amount of IO and connectivity in a single wall or desk mountable unit. Just use a mounting method that will hold it when the deck is at a slight angle, like a ridged table top or a big rubber mat top.

author: Short Circuit
author_rank: Frequent Contributor
timestamp: April 25, 2013, 07:59:58 pm
content: You may want to read into the EU directive on maritime electronics. Don't know to what extend this is required for on board electronics, but better safe than sorry...http://europa.eu/legislation_summaries/transport/waterborne_transport/l24143_en.htm

author: lewis
author_rank: Frequent Contributor
timestamp: April 25, 2013, 08:09:09 pm
content: You might want to have a look at the fitpc - it's a fully functional PC, fanless, with no moving parts if you go SSD, and is very reliable (I use a fitpc2i and it's very good).http://www.fit-pc.com/.

author: bilko
author_rank: Frequent Contributor
timestamp: April 25, 2013, 08:22:41 pm
content: QuoteAny standard laptop will do what you want, no need even for SSD.When you are not using, store away in a neoprene case.If you need a desktop model, a good well known brand will suffice and will last at least 2 years if kept dry and out of sea spray.Mission critical, well that's an entirely different spec..

author: free_electron
author_rank: Super Contributor
timestamp: April 25, 2013, 08:36:09 pm
content: panasonic toughbook.there. i just saved you from having to build something yourself

author: Alana
author_rank: Frequent Contributor
timestamp: April 25, 2013, 11:23:06 pm
content: Thanks everyone, now i know where I'm standing with this.

author: nctnico
author_rank: Super Contributor
timestamp: April 26, 2013, 01:28:34 am
content: Quote from: Jon Chandler on April 25, 2013, 06:44:15 pmI agree. I've used standard PCs in cars and even a tank. Just make sure to protect it from strong vibrations. The problem with 'industrial' computer hardware is that despite the high price it is in fact cheap low quality utter crap and therefore very unstable. A standard PC (go for a business / workstation machine from an A brand like Dell or HP) can be bought for little money and can be discarded after a few years.

author: AlfBaz
author_rank: Super Contributor
timestamp: April 26, 2013, 03:06:09 am
content: Are you talking about a standard pc that doesn't control or process anything external, like a standard office PC?If it's on the bridge or master's/Chief Eng's office than just about any PC will do. I worked on ships (when they came to shore) for the best part of 15years and all the Office pc's where bog standard. The only mods where Velcro to stop things from falling when the ship was rolling. The only other things I suggest is that the unit is put together well and with attention to detail and make sure it has a top quality power supply with some sort of line filtering and has a large mains frequency tolerance.

author: NiHaoMike
author_rank: Super Contributor
timestamp: April 28, 2013, 08:09:09 pm
content: Conformal coat the boards and use dielectric grease in connectors to provide protection against moisture. Try to go for a single board solution if possible.

author: AlfBaz
author_rank: Super Contributor
timestamp: April 29, 2013, 12:11:36 am
content: Quote from: NiHaoMike on April 28, 2013, 08:09:09 pmI wonder what, if any, effect the change in dielectric constant with the addition of, typically thick conformal coating would have on the signal integrity, or "eye" of the numerous data signals running around on the top layer of most mother boards.I would suspect they have controlled impedance and this coating may change the specified tolerance

author: nctnico
author_rank: Super Contributor
timestamp: April 29, 2013, 07:55:17 am
content: You are right. The conformal coating will affect the transmission lines on the board. Even the solder resist has some influence and needs to be taken into account by the designers.

author: KJDS
author_rank: Super Contributor
timestamp: April 29, 2013, 09:00:32 am
content: Quote from: nctnico on April 29, 2013, 07:55:17 amThe only affect of solder resist is on loss, it doesn't measurably change the line impedance until you're at the 10s of GHz

author: george graves
author_rank: Super Contributor
timestamp: April 29, 2013, 10:22:48 am
content: Quote from: free_electron on April 25, 2013, 08:36:09 pmThis.

author: ptricks
author_rank: Frequent Contributor
timestamp: April 29, 2013, 12:04:08 pm
content: Think carefully on using a laptop, if it fails, there isn't much the average electronics guy can do to fix it except swap it out. If I did go with a laptop I would buy 3 for each ship, 2 to use, 1 for backup. Make sure to get extra power adapters also as they fail often.

author: Alana
author_rank: Frequent Contributor
timestamp: April 29, 2013, 12:13:11 pm
content: We decided to go with standard desktop PC, possibly running linux. Thanks for information.

author: AlfBaz
author_rank: Super Contributor
timestamp: April 29, 2013, 04:28:59 pm
content: Quote from: KJDS on April 29, 2013, 09:00:32 amIs it possible that you could supply some citation or background to this statement so that I may read up on the subject?My thoughts were that it was the transitions which are of importance. That is the rate of change in a signal. A frequency of 1Hz will not be affected by stray inductance and capacitance thereby having negligible impedance. if the 1Hz frequency was a square wave with sub-nano second rise/fall times then the aforementioned parasitics will yield significant impedances that may require special attention.I have a design, it's a piddly ARM running at 266Mhz accessing DDR mem at 133Mhz. Rise and fall times are about 1.5nsI ran some batch simulation integrity tests on the pcb layout, with 2 different layer stackups.One without and one with a substantial solder mask. I set the mask up as follows 0.5mm thick(about 19mils) and a dielectric constant of 3.3.I took a guess at the thickness you may deposit with a spray can and thought 0.5mm sounded about right. The dielectric constant I gleaned as a typical ballpark figure in the various conformal coating data sheets.The differences in the results are indeed smallHere's an abridged version of the results for one track on the top layer 99.25mm in lengthWithout masktotal metal delay ............ 614.797 psminimum metal Z0 ............. 17.9 ohmsmaximum metal Z0 ............. 40.0 ohmsaverage metal Z0 ............. 38.8 ohmstotal metal capacitance ...... 15.9 pFtotal metal inductance ....... 23.9 nHtotal metal resistance ....... 416.6 milliohmsSignal integrity statisticseffective net Z0 ............. 33.6 ohmsWith masktotal metal delay ............ 686.554 psminimum metal Z0 ............. 16.6 ohmsmaximum metal Z0 ............. 37.1 ohmsaverage metal Z0 ............. 34.8 ohmstotal metal capacitance ...... 19.8 pFtotal metal inductance ....... 23.9 nHtotal metal resistance ....... 416.6 milliohmsSignal integrity statisticseffective net Z0 ............. 30.5 ohmsFrom this I can see the capacitance has changed slightly and this reflects in the correspondingly small change in overall impedance.The capacitance being the only thing to change makes sense, due to the addition of the mask. Signal delay seems to have increased a fair bit but for the timing requirements of the devices on this pcb, they have very little consequenceThe thing that I'm not sure about is would the differences in impedance and signal delays be greater at GHz bus speeds and the ensuing increase in slew rates or would the margins remain similarly small

author: KJDS
author_rank: Super Contributor
timestamp: April 29, 2013, 05:20:52 pm
content: A commercially applied solder resist won't be 0.5mm thick. 0.02mm is a more typical thickness, so your calculations showing not much affect at 0.5mm would show far less at 0.02mm.It only becomes significant once that 0.02mm starts to become a significant part of a wavelength which will rarely concern any of us.

author: Mr J
author_rank: Regular Contributor
timestamp: April 29, 2013, 06:21:29 pm
content: you can get an off the shelf PC and parylene coat ithttp://scscoatings.com/It coats like a vapour deposit system, pic attached of a board submersed in water with coatingmight be over kill

author: nctnico
author_rank: Super Contributor
timestamp: April 29, 2013, 09:14:43 pm
content: Quote from: KJDS on April 29, 2013, 05:20:52 pmBut a conformal coating is usually much thicker and may be applied uneven causing a trace to have different impedances along the way.

author: AlfBaz
author_rank: Super Contributor
timestamp: April 30, 2013, 02:07:30 am
content: Quote from: KJDS on April 29, 2013, 05:20:52 pmWe are not talking about a controlled process, we are talking about manually applying a conformal coating to a motherboard.Another aspect of this which hasn't been taken into account in the above simulation is that the dielectric between pins on connectors and IC's is air(Er approx 1) and after conformal coating, the dielectric constant between these pins will have increased resulting in a higher capacitance, altering the impedance more again.Given that PCB controlled impedance tolerances of +/-10% would be the order of the day we can see that the above variance by adding the coating is just over 10%. This extra 10% on top off what ever variance already exists seems to place the controlled impedance tolerance out of specs.Furthermore timing windows for sampling buss data are very small, they are saying a 100-150ps total channel timing error. If the above simulation is anything to go on we are seeing an increase (not including the extra capacitance I mentioned earlier) of around 70ps. If we add this to existing timing variations that are close to tolerances then we start exceeding these tolerances.QuoteNot quite sure what you are talking about here. My very limited knowledge in this field disallows me to see the correlation between wavelength and dielectric thickness.QuoteI agree, not many of us are designing high speed consumer pc motherboards. Nevertheless we are in affect modifying a design where this may very well have concerned the designers. In some instances this may concern us if we are looking at very small signals as opposed to worrying about high speed.

author: KJDS
author_rank: Super Contributor
timestamp: April 30, 2013, 11:22:01 am
content: Quote from: AlfBaz on April 30, 2013, 02:07:30 amI have only been talking about solder resist.

author: Harvs
author_rank: Super Contributor
timestamp: May 01, 2013, 01:34:11 am
content: Quote from: george graves on April 29, 2013, 10:22:48 amYep, they are good (the sales guys always liked to bring them in, and promptly push them off the table onto the concrete floor from waist height, every time we saw them...)But one of our techs found a fundamental weakness. He left a pen sitting on top of the keyboard and closed the lid.

author: c4757p
author_rank: Super Contributor
timestamp: May 01, 2013, 01:37:50 am
content: Quote from: Harvs on May 01, 2013, 01:34:11 amOh crapthat sucks. Most of my laptops seems to be pretty good at either ejecting pens, or just refusing to close (without mashing it against the LCD).

author: cwalex
author_rank: Frequent Contributor
timestamp: May 01, 2013, 04:53:53 am
content: Quote from: c4757p on May 01, 2013, 01:37:50 amyeah, we do quite a few LCD replacments due to the pen / kids toy left on the k/b and lid closed, along with "stepped on the notebook, dropped it and even a fire juggler that spilt his kero and it got inbetween the layer in the front of the panel, you could push the little bubbles around with your finger and the LCD still worked" there are heaps of other creative ways people break there stuff.I think most panels would take a pen ok if you didn't try to force the notebook closed when you felt the resistance but some people feel that it doesn't want to close and give it an extra hard press to try to close it.Worst notebook repairs from my memory are dog peed on it, toddler peed on it and the worst one, my son vomited on itwe drew straws to see who did that job!

author: SeanB
author_rank: Super Contributor
timestamp: May 01, 2013, 05:54:22 am
content: got tossed up on - take out back and wash with hose first, then pull out HDD and place in desiccator and dry for a week. Toss the rest. If brave take out HDD first then toss the rest. Always wear disposable gloves.

author: AlfBaz
author_rank: Super Contributor
timestamp: May 01, 2013, 05:58:44 am
content: Think outside the square people!... give it to your dog for an hour, he'll get most of the chunks