large scale project

Using Arduino Project Guidance
21

remous1:
still no one answered the real question which is..is there an equivalent for arduino for more serious projects? something that do the same job but more secure ? that's simply my question and i don't know why everyone is bothered with the project details which i didn't ask about

The reality is: it doesn't really matter. In the US, ALL devices that are used in a hospital or medical facility MUST be made by a FDA certified facility. No chance of finding such an Arduino. An Arduino is perfectly capable of doing research projects such as you are suggesting.
My company did many R&D projects for medical research, but could not be considered for ANY production work.
So go ahead ahead and use any Arduino for your research. No problem. In the end, you will have to sell your research to a company that is already FDA certified in order to make a product that can be used medically.
Actually, the doctor you referred to will have the rights to anything you develop, not yourself.
Paul

22

Still no one answered the real question which is..is there an equivalent for Arduino for more serious projects? something that do the same job but more secure ? that's simply my question and i don't know why everyone is bothered with the project details which i didn't ask about.

You are missing something important: Suppose there existed (maybe it does, but I doubt it) a completely certified, fully medically capable board suitable for life critical functions, like you are hoping for. That board might be OK from an electrical point of view, but it will still be YOUR software on there and YOUR peripherals attached to it with wiring YOU designed and implemented. No board manufacture can extend their certification to the bits you designed, you have to do that.

23

It would help to know a bit about the hospital you're talking about. Is this a modern hospital in a developed country, or an impoverished field hospital in a remote area of an underdeveloped country?

Also, a proper safety evaluation of a monitoring system involves much more than just the Arduino (or whatever device is at the heart).

S.

24

About 300 years ago, a device was invented called a pressure gauge, when the pointer on this device was near zero, it meant the container was near empty. But, there has to be a responsible, semi-intelligent human to READ the gauge and take appropriate action. THERE'S the problem.
"I don't want to be BOTHERED by the responsibility of another human's well being, I want automation to do it FOR me".

25

remous1:
still no one answered the real question which is..

That has been answered several times, you just don't want to read the answers. Arduino is not suitable for your purpose. You, actually probably not you, can make a medical device using the same ATmega 328 chip that would be 100% kosher - and with your programme. There is nothing exclusive about the chip, it may well be already common in portable medical devices, along with guided missiles and god knows what all else. What's more, that specially made controller module would probably be cheaper. I understand a working "arduino" can be made for $2.

I recall there is an industrial-strength Arduino, but I believe it is still just a development board but in a bulletproof box, and it is seriously expensive.

26

There is a PLCduino
Not krazy expensive.
Develop on your UNI/NANO
Then port over.
Not rocket surgery

27

Liquified gasses maintain constant pressure based on temperature.
Weight or liquid level are the only ways to measure

28

dave-in-nj:
Liquified gasses maintain constant pressure based on temperature.

While this is true, oxygen in K-cylinders (the normal means of distribution) is not liquified; it is a gas under several thousand psi.
S.

29

srturner:
While this is true, oxygen in K-cylinders (the normal means of distribution) is not liquified; it is a gas under several thousand psi

As per #16 of course. :sunglasses:

30

Paul__B:
As per #16 of course. :sunglasses:

Roger that.
I suppose there is no guarantee that the OP's hospital isn't using LOX dewars similar to the very common LN2 dewars, but I think it highly unlikely. LOX is dangerous stuff. If it gets into contact with organic material it can make a bomb, and I mean a real, high-order detonation bomb, not "just" a pyrotechnic display. Seems unlikely that a hospital unable to even monitor its oxygen level would be flirting with that stuff...
S.

31

The AVR chips are probably perfectly suitable, however ‘Arduinos’ may have limitations because of the hardware form.
All microprocessors and controllers have disclaimers about life-critical applications. The mitigation of those warnings can only come from your system design and software... Fault indication / tolerance / redundancy, auto-recovery etc.

This includes everything from the power cable to the sensors and actuators, enclosures etc.
It’s your responsibility to define the safe operating parameters and limits, and the test protocol to prove those values.

The scope of the compliance requirements will be determined by the relevant approval authority - e.g. the health department etc...

32

srturner:
While this is true, oxygen in K-cylinders (the normal means of distribution) is not liquified; it is a gas under several thousand psi.
S.

even under several thousand PSI, if the vessel gets cold, or hot, and the volume does not change, the pressue does.
pressure, volume, temperature. if one is fixed the other 2 change with inverse of the other.
bottom line is that if you want to measure the pressure of oxygen, your sensor would have to be factory rated for contact with oxygen on the wetted surfaces. and that additional certificatin might cost more than the rest of the hobby electronics.

33

srturner:
I suppose there is no guarantee that the OP's hospital isn't using LOX dewars similar to the very common LN2 dewars, but I think it highly unlikely. LOX is dangerous stuff.

Well, I don't park next to them because - well - my designated parking area is actually the other side next to the main block but at the local private hospital, the oxygen Dewar is right in the corner of the car park in line with the entrance with the LNG tank just behind it so that could be considered a bit of a concern but frankly, both are dead safe.

They are of course in line with the entrance so the delivery trucks can back straight in. :sunglasses:

Obviously there are "Medical Gas Supply" annunciator panels in the theatre corridor (and probably in the ward area too - I haven't really noticed) as in any "first world" hospital. There is of course, a pair of cylinder banks for backup, size "K" cylinders sounds about right, at least three per bank. Haven't taken much notice any time recently, I am usually reading the paper at lunch. :grinning:

34

Can somebody PLEASE cite a reference to measuring the weight of a vessel and the "life-critial" that keeps getting tossed around. not what one 'feels' concerned about, but some actual reference to regulations ? NFPA, Electrical Code, anything ?

I used to do explosion proof controls and the simple, and I mean SIMPLE, requirement was:

" IN THE PRESENCE OF ..... [ state here the hazzard ].....

working with Fortune 50 companies, we would just put the stuff in the closet down the hall, besides who in their right mind would put an electromagnetic relay or heater wires in an explosion rich atmosphere ? ( OK, Honeywell and Apollo-13, but that doesn't count)\

example :
NFPA 497. You'll find that in open areas, the Class 1, Division 1, area is limited to a distance 5' from the source. The Class 1, Division 2 area is limited to a distance of 10' from the source

The reason they called it the 'control room' and not the 'hazardous lab atmosphere room' was because THAT is the way it is done.

or :
Where Class I liquids are stored, handled, or dispensed, electrical wiring and electrical utilization equipment shall be designed and installed in accordance with the requirements for Class I, Division 1 or Division 2 classified locations, as set forth in 8.3.2 and in NFPA 70, National Electrical Code ." NFPA 30A 2015, 8.3.1

and yes, we put ground straps on anything and everything, even plastic sensors. one facility had a safety plackard : this facility has not had an explosive accident since 1937. (the day it was opened)

and, we had entire buildings built adjacent to the lab, with the walls solid reinforced concrete and a hinged roof for the release of pressure in the event of an explosion. other building had blow-out walls for the same purpose.

bottom line IT CAN BE DONE.
we brought the concerns up, the facility WILL REQUIRE code be met as would anyone with more than 2 years in training, ie : EVERYBODY ELSE involved in the engineering of the project.
we are 32 posts into warnings, at some point one has to say we warned the guy.

all we needed to say is :
BEFORE YOU ATTEMPT to GO NEAR the thing, HIRE A PROFESSIONAL that knows the code and laws so you don't cause problems. NEVER rely on a web forum for advice on safety or the use of anything that might be unsafe.
we are NOT LICENSED and have NO rating to advise you on the safety issues, we are a hobby group and can only advise you on how we would do it with hobby parts and supplies in a hobby way, in a hobby environment. if you are trying to copy a product or system, SEEK OUT PROFESSIONALS who are licensed in that area for your own protection as well as the protection of others.

35

Paul__B:
Well, I don't park next to them because - well - my designated parking area is actually the other side next to the main block but at the local private hospital, the oxygen Dewar is right in the corner of the car park in line with the entrance with the LNG tank just behind it so that could be considered a bit of a concern but frankly, both are dead safe.

I somehow misread your other post (#16) to mean that hospitals would not have dewars, when in fact it sounds as if they do (or at least some of them do). In that case, of course, pressure monitoring will not work. My bad. But I'd still like to hear some details of the hospital in question here.

S.

36

This is a private hospital with IIRC, about 70 beds (if I remember, will check on Monday :grinning: ) and six operating theatres, dealing mainly with surgical patients. I would say with reasonably certainty, that almost all hospitals of and above this size would be using a Dewar for oxygen supply as a matter of economy - and reliability.

There used to be a similar Dewar by the main road next to the settling ponds for the local sewage treatment plant, notable for the fog from its pressure relief. It had not occurred to me until now that it disappeared a few years back. The point is, they are not at all uncommon and whilst they do carry the "Oxidising agent" warning sign as do the trucks and are fenced off, are not considered hazardous.

37

Paul__B:
This is a private hospital with IIRC, about 70 beds (if I remember, will check on Monday :grinning: ) and six operating theatres, dealing mainly with surgical patients.

Sorry, I was unclear. I meant the OP's hospital. So much depends on that.
I have an inlaw who was a missionary in Ghana for many years. I don't know if their med facilities would be termed a "hospital" or not, since they seemed to barely have two clean scalpels to rub together. Improvisation and scrappiness were necessary for survival (sometimes in a literal sense). Not everyone in the world has the luxury of modern infrastructure, stringent safety regs, and a staff member whose function includes routine checkups on the O2 supply. But I have no idea where along this spectrum of facilities development the OP's hospital lies.
S.

38

Of course. :astonished:

39

@remous1

I've been thinking about what might do the job; possibly you need a PLC, programmable logic controller. PLCs are specifically designed for use in industrial applications and are likely to meed the specifications you need. I cannot tell you any more than that, I know nothing more about them. If there were someone here who knew what you need to know I suspect they would have already said something. Search for manufacturers of PLCs and tell them what you are doing, they might recommend one of their products.

40

dave-in-nj:
even under several thousand PSI, if the vessel gets cold, or hot, and the volume does not change, the pressue does.
pressure, volume, temperature. if one is fixed the other 2 change with inverse of the other.
bottom line is that if you want to measure the pressure of oxygen, your sensor would have to be factory rated for contact with oxygen on the wetted surfaces. and that additional certificatin might cost more than the rest of the hobby electronics.

Charles's Law: P1T2=P2T1, where T is absolute. If we make the assumption that the cylinders are stored outside in a 4-season climate, that might mean a temperature range of maybe 270 to 320K. That is less than 20% variation in pressure over the entire range of temperature. But the pressure difference in going from a full cylinder to dangerously low is perhaps 3000 psi to ... what, 100 psi ... many fold difference. So I don't think temperature variation would be a serious objection. Furthermore, if +/- 20% is not sufficient accuracy, it would be easy to correct for temperature via a temperature sensor.

However, it is absolutely true that a pressure sensor would have to be rated for use with high pressure O2, as I noted in #8. It is also true that if the O2 source is liquified, then pressure monitoring will not work at all.
S.