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Old 8th Feb 2017, 11:54 am   #1
mole42uk
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Default Mobrey gas tester

Has anyone seen one of these before? It's a Mobrey Combustion Analyser MCA 2 which I bought at an auction, but even the manufacturers don't know anything! The manufacturing date is March 1985.

It is battery operated (8.4V NiCad) and has two large PCBs full of TTL and LSI. So far I have only confirmed that the battery charges and the displays work but there appears to be some functions that do nothing.

Any help most appreciated!
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Old 8th Feb 2017, 11:57 am   #2
Nicklyons2
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Default Re: Mobrey gas tester

I do love it when the actual manufacturer denies all knowledge. I've had it with Philips twice - I wonder who they think is making gear with their name on it?
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Old 8th Feb 2017, 12:18 pm   #3
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Default Re: Mobrey gas tester

They are probably full of hot air.
Philips are known for disowning their product.
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Old 8th Feb 2017, 5:02 pm   #4
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Default Re: Mobrey gas tester

Perhaps it was made before Mobrey became Bestobell Mobrey, if that was the case. We've had threads before where old records had been "lost" after a takeover. As for Philips, they must have made thousands of products in factories all over the world, it's hardly surprising that some are unknown elsewhere.
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Old 8th Feb 2017, 5:11 pm   #5
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Default Re: Mobrey gas tester

It's marked "Bestobell Mobrey" on the front panel.
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Old 8th Feb 2017, 9:40 pm   #6
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Default Re: Mobrey gas tester

If it's more than 10 years since the last one was produced, there's no requirement for any sort of equipment to be supported by the manufacturer. Even if they're still around, they may well have scrapped any old documentation or perhaps more likely simply failed to keep any record of it.
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Old 8th Feb 2017, 9:54 pm   #7
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Default Re: Mobrey gas tester

Mobrey have been through several different owners in recent times; Bestobell Mobrey, KDG Mobrey and now Emerson Mobrey.
The last time I rang them they couldn't answer a question about some brand new equipment of theirs I was installing.

That machine of yours looks like something they'd use to test your boiler
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Old 8th Feb 2017, 9:57 pm   #8
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Default Re: Mobrey gas tester

Very interesting. Probably used to check domestic heating boilers and probably works by infra-red spectroscopy (infra red gas analyser =IRGA). Instruments like it go back for a very long time, even had valves in them! I pulled a few apart. In the days before hi-tech stuff was helium leak-checked with mass spectrometers, they used IRGA's with nitrous oxide.

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Old 9th Feb 2017, 10:36 am   #9
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Default Re: Mobrey gas tester

I suspect it was a boiler test set, the selector for heavy oil, light oil, natural gas or solid fuel would suggest that. I want to use it to test the exhaust of my classic car!

There are two gas sensors, one is by City Technology, patent number 1571282 which seems to be a permeable-membrane type oxygen sensor and has three wires, the other is un-identified but has only two wires and is probably the CO sensor.

The LSI chips are 7106 LCD display drivers, everything else is CMOS or op-amps. There are some functions that work, but not many, and the displays, after settling, just display a 1 in the left-hand position. I'll try the test pin on the 7106's but I'd expect them to work.

I think there's probably a simple interruption in the power supply line because it sems that the analogue and CMOS isn't talking to the display drivers. There is a 7805 on a heatsink wired as a current limiter for the battery charge circuit!
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Old 9th Feb 2017, 12:49 pm   #10
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Default Re: Mobrey gas tester

As to testing the exhaust of your classic car, I think your best option would be to take it to an MOT tester! If it doesn't have a catalytic converter, it will show carbon dioxide, water vapour, and rather more carbon monoxide than you might wish for, or which would be permitted on a modern car. You might not want to know that!

Yes, it's a boiler flue gas analyser to check the products of combustion emitting from the flue of a central heating boiler. As you might expect, time moves on and nowadays they are generally hand-held instruments about the size of a multi-meter, and often will print out the results of tests, as well as storing the test results. Typically they test boilers fuelled by Natural gas (methane), Light oil (28/35 sec), Propane, Butane, LPG & Wood pellets.

They carry out a wide range of tests:

Carbon dioxide (CO2)
Carbon monoxide (CO) 0-2,000ppm
Flue and inlet temperature
Differential pressure (80mbar)
Calculates:
Oxygen (O2)
CO/CO2 ratio
Poison index
Efficiency

Typical example by Kane: http://www.jmwlimited.co.uk/Kane_455..._Analyser.html

I don't know if the following remarks and reminiscences are a bit too far off topic and irrelevant. I'll leave that to the mods' judgement - I'm happy for them to be deleted if need be as they add nothing to the info about the actual Mobrey tester - only why such testers are necessary:

The products of combustion from a gas boiler working properly are carbon dioxide and water vapour, with a small trace of carbon monoxide and oxygen. If there isn't sufficient oxygen entrained into the burner, incomplete combustion arises. Methane is CH4. The H4 needs 2O2 to become H2O and the 'C' needs O2 to become CO2, but if it can't get it, it becomes CO, which is of course highly dangerous. (Carbon monoxide is 200 times more attractive to the lungs than is oxygen and hence, it's quickly absorbed into the bloodstream).

It's been mandatory for all gas boilers to be room-sealed for many years. What was called 'balanced flue', which have a concentric flue in which air is drawn into the combustion chamber, and flue gasses are emitted. There are still millions around - only about 60% efficient at best, and with a wasteful permanent pilot too.

The main danger was from open-flued boilers which were often sited in kitchens, where ironing takes place, and pets such as dogs and cats are often present. The fibres of pets and from ironing get drawn into the burner which can make the boiler hazardous.

Gas burners work on the 'venturi principle' - the jet of gas going into the burner draws air into the throat of the burner which mixes together and burns on a mesh or perforated burner head. When boilers (or any appliance such as a cooker or fire) designed for use on coal gas are converted to natural gas, the volume of gas required is halved, so the jet of gas into the burner is much less, and hence, it's ability to entrain air into the burner is much reduced.

The flame speed of natural gas is far less than coal gas, so with insufficient oxygen into the burner, incomplete combustion occurs generating carbon monoxide and the flame can lift off the burner (rather like a cigarette lighter when turned up too high), causing soot to form on the heat exchanger. Not helped by animal fibres and dust from ironing being drawn into open-flued boilers, blocking the burner mesh or holes. If the carbon monoxide enters the room rather than going up the flue, it can soon be fatal.

Nowadays, all boilers must be room-sealed fan-assisted condensing boilers, both for efficiency, (90% + of the gas is turned into heat) and for safety. A condensing boiler has a secondary heat exchanger to extract the heat from the products of combustion ('fumes') so that the hot H2O vapour condenses to water and is drained away, leaving mostly CO2 into the atmosphere.

I spent my career in British Gas, some of which was in the labs during the natural gas conversion programme, designing and testing burners to convert obsolete appliances designed for coal gas to get them to work on natural gas. Open-flued boilers were a particular problem due to their domestic settings outlined above. We used to check the flue with 'Draeger tubes' - glass tubes which you snapped off the end, and with a hand-held squeeze pump suck air into the tube to check the level of CO and CO2. The boilers back then would never have passed current tests.

From the late 1970s to the late 80s I was BG service manager at Sheffield. I used to attend coroners' inquests to give evidence several times a years where fatalities - often multiple - arose due to poorly maintained appliances, mostly open-flued boilers or wall-mounted gas fires. (So often in fact that I used to receive a Christmas card from the Coroner's Officer).

I always wondered on those tragic occasions, why so little was fuss was made and so little done about it in terms of appliance design and mandatory tests, so it's reassuring to see how far things have progressed over the years to make appliances far safer and more efficient, and to introduce mandatory landlord checks on gas appliances. (It was a landlord jailed in Hull for manslaughter due to a fatality in a student flat which I believe finally caused such mandatory checks to be implemented).
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Old 9th Feb 2017, 1:03 pm   #11
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Default Re: Mobrey gas tester

Super information, thanks David.
We also have a CO monitor in the room with our gas boiler.....
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Old 9th Feb 2017, 6:24 pm   #12
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Default Re: Mobrey gas tester

David, you must come from a similar age group to me. I was responsible for conversion to NG of a number of pottery kilns back in 1969.
But back on topic. Most gas analysis equipment has a cell for each gas type, usually of limited life, and either NLA or so expensive you would weep, so it may be just scrap.
I did design a simple gas analyser based on a Bosch Lambda sensor, but it would not work. It had a little fan operated arrangement to draw the gas thro. Subsequent advice suggested it needed some pre-heat, as the internal controlled heater was inadequate on its own. All gas analysers need filtering for soot etc (glass wool in a tube is normal) and usually have a water trap as well.
When I first checked gas kiln atmospheres, I used an Orsat gas analyser. Large glass apparatus, sulphuric acid used to contain the gas sample, caustic potash to extract the carbon dioxide, followed by alkaline pyrogallol to remove the oxygen, and finally alkaline cuprous ammonium chloride for any carbon monoxide.
A 100ml sample of gas was contained, then each test as above removed the "percent CO2", ditto O2 and finally the CO.
Later I had use of a Servomex oxygen analyser (based on oxygen's paramagnetic properties) which sufficed for all burner settings when using air blast burners. Much quicker than the 10 minutes per sample with the Orsat.
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Old 9th Feb 2017, 7:35 pm   #13
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Default Re: Mobrey gas tester

If it seems that this isn't using an infra-red cell for the CO, then the technology which followed was mostly based upon tin oxide semiconductor sensors, but I don't know whether they proved to be as good as originally hoped. I also recall now that O2 cannot be analysed by infra-red. Can you put up a picture of the sensors?

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Old 9th Feb 2017, 7:40 pm   #14
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Default Re: Mobrey gas tester

It's in at work, so I'll have a go at pictures tomorrow..
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Old 10th Feb 2017, 9:29 am   #15
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Default Re: Mobrey gas tester

Here's the pictures:

The contacts on the LHS of the 'City Technology' sensor are actually part of a jack on the panel behind!

The black tube, which I think is the CO sensor, has a label with "E8202" on one end.
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Old 10th Feb 2017, 2:01 pm   #16
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Default Re: Mobrey gas tester

If my eyes are not deceiving me, then the "City Technology" sensor has a label, albeit a bit worn, that states that it is a carbon monoxide sensor. You just have to be able to read upside-down.
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Old 10th Feb 2017, 2:05 pm   #17
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Default Re: Mobrey gas tester

Yes, it's quite a lot easier to read when it's in my hand!

I mis-typed the earlier post, in that I should have written that I think the black cylinder must be the oxygen sensor.

I have tested the 7106 drivers and all three work and all the LCDs work. There must be a power problem somewhere upstream of them since they are not displaying any useful information, except the CO/BAT display with indicates a sensible-ish voltage when BAT is selected.
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Old 10th Feb 2017, 3:41 pm   #18
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Default Re: Mobrey gas tester

Neither of those two cells look at all familiar. The City cell has lots of bolts holding it together so looks like it is clamping down on a gasket or 'O' ring so may contain a liquid? Also, the corrosion on the bolts suggests that some has escaped, so that looks as if it is some kind of "wet" electrochemical cell. If so, it may have a finite lifetime before it needs a "re-fill"?

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Old 10th Feb 2017, 3:47 pm   #19
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Default Re: Mobrey gas tester

City Technology still exist:

https://www.citytech.com/

might help ID the way the sensor works?
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Old 10th Feb 2017, 5:34 pm   #20
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Default Re: Mobrey gas tester

CO sensors in modern flue gas analysers have a life of a year or two, they 'aint cheap either.

For example https://www.trutechtools.com/03900115
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