Flame Rectification | How To Test | ACS Gas Learning NGCFE
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- Опубликовано: 1 май 2024
- #Gas #ACS #Plumber Flame rectification is one of the lesser understood types of flame supervision devices that we cover on gas training. At National Gas Centre for Excellence, students often get confused when we talk about converting voltage and current via a flame as if its some sort of wizardry.
When we break down the process, it becomes a little easier to understand. At some point, we will all come across a faulty boiler indicating a flame failure fault or an ionisation fault (an EA or FA fault on our Worcester 30i ERP for example). One potential cause of both faults could be poor or no flame rectification.
Most engineers are familiar with the firing sequence of a boiler. The PCB sends power to the gas valve and spark generator to create a flame. There is another circuit being established by the PCB that less engineers are familiar with.
The PCB sends a moderate AC voltage to the flame rectification probe (usually around 100v ac however this can vary). When a flame has been established at the burner, the flame engulfs the rectification probe and conducts the voltage, rectifying (changing) it from AC to DC current in the process. The DC voltage then travels back to the PCB via another wire (sometimes an earth wire) and completes the circuit.
Once the PCB registers a DC current being present, it knows that a flame has been established and stops sending power to the spark generator. Should the PCB stope receiving DC voltage / current for any reason, it will stop sending power to the gas valve, stopping the supply of gas to the main burner in the process. After a number of failed ignition process’, the PCB will go to lock out and present an ignition or ionisation fault.
It is the process of the voltage changing from AC to DC and the board receiving the DC current that monitors the presence of the flame. The only way in which the PCB can receive DC current is via a flame completing the circuit at the main burner.
We can use out multimeter to test for DC voltage by connecting it in series between the rectification probe and the rectification lead. Any DC voltage can then pass through the multimeter, being registered in the process. We can also use the micro-amps setting to do this if we have a multimeter with this function available.
If a boiler goes to an ionisation fault on its ignition sequence, then it is likely to be caused by a faulty component like a gas valve, ignition probes or spark generator, however if we can see or hear a flame being established, then we should also test to see if the rectification probe is conducting the voltage and subsequently being registered by the PCB.
If the boiler is going to fault later on in its operation sequence, then its possible that the DC voltage / current is being lost at some point. Potential causes for this include a poor flame (vitiated), a MIN burner setting being too low or a poor connection on the rectification circuit.
Should anyone wish to learn more about fault finding or other courses offered by National Gas Centre for Excellence, please contact us on 01924973260 or by visiting our website at www.NGCFE.co.uk . 
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Excellent and well explained. A couple of comments - firstly I would never dial through the multimeter settings whilst connected to a live circuit - turn off or disconnect the meter. You will usually get away with it but you can blow fuses in some meters (believe me with students I have changed 100s of them!). Secondly there is the usual confusion about voltage (across) and current/amps (through). It does not really affect the understanding here. For the very observant connecting the meter in series and measuring a voltage - you were lucky that things still worked as normally meters will pass almost no current at all at this setting as an 'ideal voltmeter' should be an infinite resistance/break in the circuit, but the currents are so low you get away with it here. Only comments - not a criticism at all. Your explanation was excellent!
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Very helpful. Made more sense to me today, than it did last week. Good insight
Class act here ..many thanks for your efforts lads 👌😎
Thats measuring “potential difference” and that meter is very good to have only 2 ports to automatically switch between parallel & series circuit. For the older meters you have to take out the probe and slot it into the common and the Amp symbol. The flame converting into DC is science, I love this stuff. Not only will you get burnt but get a shock (if current was right). Would discovered this ? Epic!
The video is great in fault finding. Would like to see these readings in manufactures servicing booklets so we don’t have to keep calling them for it.
Really good video. Explains it perfectly cheers guys 👏👍
Great Video Allen / NGCFE 🔥👍🏻
Great video! Learned a lot thanks
very helpful thanks
Really good video. Explains it perfectly cheers
Glad it helped
Allan Hart how did he set the multi meter probes on the rectification leads
this video is been a missive help in understanding flame rectification for my MLP/ and ACS preparation do you have a video demonstrating the basic principle of gas controls? thank you
Would have been nice to see how he set the multi meter up
A voltmeter is never used in series with a circuit, as this tells you nothing, other than the volt drop across the meter itself, which will vary from meter to meter depending on its internal resistance (ohms per volt).
The only way to properly check this circuit is with the ammeter in series (as shown) or the voltmeter between ground and the ionisation probe, though the voltage shown on the meter may be ambiguous due to it been half wave rectified.
Correct.
Thanks for the feedback guys. Always happy to learn from other engineers.
Just a question. If the flame wasn’t present, would you still get a Vdc reading?
Totally agree that micro amps is how most manufacturers suggest that this test should be should be carried out. It’s just a shame that only the high end (and priced) multimeters have that setting.
Very true, the meter in the video is connected in series and yet set to volts dc, I don’t think the reading shown on the meter is of much value from a diagnostic perspective. Good demo otherwise.
@@MrIsrar626
Digital meters tend throw up a lot of display garbage at a times, unlike the old analogue meters. For some uses some guys still use analogue meters.
The meter in series, as been noted, does read the amps.
If you do not know what the AC voltage to the flame rectification probe should be or the DC voltage coming back. Just reading that there is AC going to and DC coming back, gives a ballpark indication that things may be working OK on the probe side. That would mean reading the voltages correctly.
Agreed! Do you think that the internal resistance of the meter was such that it could still pass a few uA when in voltage setting so the circuit (luckily) still worked?
A video on 16.9 would be a good.
How to check high efficiency furnace or low ?
👍
Cool. Nice video. Some boilers have the capability of showing you the flame strength.
Like that exact boiler you mean 😂! Coz that one does! It’s in the menus think anything under 35 is suspect but check the book!
Anything under 400
Hi Allan
Good video
Only engineer voice is lowest
Regards
Faruk
Allen different types of heat exchangers. Japanese Korean and European and American. Positives and drawbacks
Really to get your electrical terms in line, your mixing things together. you can’t have 100v of ac current . You can’t put a meter in series and check voltage. You can’t have. 63 volts of dc current. I understand where your going with it, but it’s really going to confuse someone who’s unsure.
Thank You
10 quid says the burner gasket needs changing
The test with the multimeter at 6:40 was not the _return_ to the pcb. It was the _supply_ to the flame rectification probe from the pcb. The return is the green wire.
Did I get that right?
You are correct in what you are saying but this is reading the circuit. Thanks.
@@AllenHart999
It is *AC* current *to* the flame rectification probe from the pcb. The flame changes the electrical voltage from AC to *DC,* as it conducts through the flame, then it returns back to the pcb.
The meter is a Fluke 116. The setting _was_ on DC. I can only assume there was a reading of DC as the multimeter was connected in *series* by Michael to read voltage, which is not how you read voltage.
Does it rectify with temperature of the flame?
@@dannydobson2675
Not that I am aware of. The flame acts as a diode. Goes one way not the other. The DC will be pulsating DC not pure DC like out of a battery. The setting on the multimeter indicated pure ( - ) and
pulsating (- - -) DC.
I am a bit confused about that too. I thought he said the probe is AC and the green earth wire carries the DC current back to the board. I too am missing something.
Hi Allen could u just talk us through where the actual multi metre probes went .I know u had a crocodile clip on the red but where did u put the black .its quite hard to see the top of boiler .thanks