Arduino Forum

Using Arduino => Programming Questions => Topic started by: Joes on Feb 11, 2012, 05:27 pm

Title: ionisiation?
Post by: Joes on Feb 11, 2012, 05:27 pm
hi there

i have been making a control unit for gas/oil boiler i would like to try and get the ionisation probe to work with my aduino. i didnt know if anyone had tried this or has got any information on someting like this?

thanks
Title: Re: ionisiation?
Post by: robtillaart on Feb 11, 2012, 05:41 pm

Can you share some pictures and/or code sofar (to get a better understanding of what you want to accomplish?
Title: Re: ionisiation?
Post by: Joes on Feb 11, 2012, 06:08 pm
just found this link just a bit of general info about it. i havent gor any pics just a piece of ceramic with a metal bar going through it which is in the flame and th ceramic insulates it from the chassis
didnt know if anybody has played with this is the arduino world

http://www.petervis.com/electronics%20guides/polonium%20detector/ionisation%20chamber.html
Title: Re: ionisiation?
Post by: Grumpy_Mike on Feb 11, 2012, 06:13 pm
Assuming you stick this in a flame, it will act as a conductor when it is in a flame and an insulator out of it.
So just put it between the input and ground and have an external pull up resistor of 1K.
It should work fine in a digital input.
Title: Re: ionisiation?
Post by: Joes on Feb 11, 2012, 06:33 pm
ok cool
just to clarify where exactly should i put the resistor?

thanks
Title: Re: ionisiation?
Post by: Grumpy_Mike on Feb 11, 2012, 07:09 pm
From the input pin to +5V.
Title: Re: ionisiation?
Post by: Joes on Feb 11, 2012, 07:20 pm
ok thanks will have to have a play with that when i get time
Title: Re: ionisiation?
Post by: Joes on Feb 17, 2012, 05:46 pm
hi again
i have made bit of a rig up and ran your theory above and i couldnt seem to get it to work at all. i think there is a bit more to it than i originally thought ?
Title: Re: ionisiation?
Post by: Grumpy_Mike on Feb 17, 2012, 08:02 pm
A flame consists of ionized gas, if two conductors are placed in it then current will flow.
Many years ago I put an audio signal through a flame simply by placing it in series with the speaker connection.

If you are not getting anything from it try and measure the resistance of the probe and sheath, it might me made of some resistive materiel so that it works on a higher voltage.
Title: Re: ionisiation?
Post by: kunkmiester on Feb 18, 2012, 08:26 pm
There will also be issues with the conductivity of the probe and flame, and your 1K resistor might be a bit much, if the probe's resistance is high enough.  Measure the resistance, and use Ohm's law to find the power drawn.  You want to make sure the power is below the max for the arduino, but high enough to register.  If the voltage is dropping too much to register, or the current is too high and tripping protection or something, it wouldn't work.
Title: Re: ionisiation?
Post by: MarkT on Feb 18, 2012, 09:48 pm
Quick google suggests 100Mohms is a good starting point...  A flame is not that good a conductor!

Also found this fascinating page: http://www.sparkbangbuzz.com/flame-amp/flameamp.htm (http://www.sparkbangbuzz.com/flame-amp/flameamp.htm)
Title: Re: ionisiation?
Post by: Joes on Mar 01, 2012, 07:55 pm
hi there
i have been playing with different resistances. im up in the 2000k to get it to work on my test rig on my finished product i might be able to get it lower than that but i was wandering is it ok to use these sorts of resistances?
Title: Re: ionisiation?
Post by: Grumpy_Mike on Mar 01, 2012, 11:32 pm
Well it won't do any harm but it might be a bit suceptable to noise.
You can try a higher voltage with a 5.1V zenner to protect the input.
Title: Re: ionisiation?
Post by: Joes on Mar 02, 2012, 07:17 pm
what switch the live instead of the 0v?
Title: Re: ionisiation?
Post by: Grumpy_Mike on Mar 03, 2012, 09:15 am
Pardon?
Title: Re: ionisiation?
Post by: Joes on Mar 03, 2012, 04:32 pm
how would i wire it for high voltage?
diagram
Title: Re: ionisiation?
Post by: Grumpy_Mike on Mar 04, 2012, 10:29 am
Just put a high voltage on one terminal, with a 1K resistor in seriese with the input. Then wire a zenner between input and ground. The other end of the sensor goes to ground.
Title: Re: ionisiation?
Post by: Grumpy_Mike on Mar 05, 2012, 05:45 pm
No like this.
Title: Re: ionisiation?
Post by: Joes on Mar 05, 2012, 06:08 pm
ok thanks
what do we call high voltage?
Title: Re: ionisiation?
Post by: PaulS on Mar 05, 2012, 06:10 pm
Quote
what do we call high voltage?

Dangerous.
Title: Re: ionisiation?
Post by: Grumpy_Mike on Mar 05, 2012, 08:48 pm
Anything higher than 5V.
The higher the voltage the more current the flame will conduct.
Making the resistor higher will make any change in current a larger change in voltage and the easier it is to detect.
Title: Re: ionisiation?
Post by: Joes on Nov 21, 2012, 06:40 pm
sorry to bring this back up again i had got this working but its extremely unstable as there is not much movement on the arduino, i was using 1500k resistor to even get it to work i cant seem to add any more than that or it seems to go the other way so i dont know how else we could make this work more reliably and give us more of a range on the arduino
i measured the resistance of the probe and flame was 1400k and my supply voltage i was running 17.11 and im getting back on the other end 1.65V so hell of a drop?
Title: Re: ionisiation?
Post by: Grumpy_Mike on Nov 21, 2012, 09:48 pm
You need to use an op-amp to make the signal from the flame bigger.
Start of with a gain of about 100 and see how you get on.
Title: Re: ionisiation?
Post by: Joes on Nov 23, 2012, 05:04 pm
ok thanks for that i have had a bit of a play and come up with this
http://s906.photobucket.com/albums/ac270/Joes-110/?action=view&current=Untitled.png
but now we have gone to the other way now it is to sensitive and can not seem to dye down any idea?
Title: Re: ionisiation?
Post by: Grumpy_Mike on Nov 23, 2012, 09:12 pm
Three things wrong with that circuit.
1) It only has a gain of 2, see how to calculate the gain of a non inverting op amp here:- http://en.wikipedia.org/wiki/Operational_amplifier (http://en.wikipedia.org/wiki/Operational_amplifier)
2) You in effect have a floating input, that is the input is very high impedance and is picking up all sorts of interference.
3) That sort of circuit will only amplify voltages, you are in effect putting a variable resistance on the input you are not inputting a voltage.

Try this. +ve input of amp connected to two 1M resistors, one goes to +5 and the other ground. Then feed this point and ground at your flame.
Change the resistor that goes from the -ve input to ground to a 10K. What sort of op amp are you using.
Title: Re: ionisiation?
Post by: Joes on Nov 23, 2012, 11:01 pm
thanks for the reply i am using a LM358 as this is what i had lying around.
ok can you draw that as this is all a bit now to my and will be easier to understand thanks
Title: Re: ionisiation?
Post by: Grumpy_Mike on Nov 23, 2012, 11:27 pm
You might have to play about with the value of the top 1M

Title: Re: ionisiation?
Post by: Grumpy_Mike on Nov 24, 2012, 05:54 pm
Sorry I forgot about the DC bias. Take the resistor that goes to the -ve of the op amp to ground and disconnect it from ground an put it to the wiper of a 10K pot with the two ends to ground and +ve.
This will allow you to adjust the output to be mid range with no flame, then you should see it move in the flame.
Title: Re: ionisiation?
Post by: Joes on Nov 24, 2012, 10:30 pm
like that?
Title: Re: ionisiation?
Post by: Grumpy_Mike on Nov 24, 2012, 10:41 pm
No the end of the pot goes to the +ve supply not the +ve input of the op amp.
And the 100K still goes to the -ve input of the op amp.
And you still need the 10K resistor going between the wiper and the -ve input of the op amp.
Title: Re: ionisiation?
Post by: Joes on Nov 24, 2012, 10:48 pm
ok cool i got it now thanks, will have to get some resistors in and have a play
Title: Re: ionisiation?
Post by: Joes on Dec 01, 2012, 07:04 pm
right i tried that and it didnt seem to work when adjusting the pot it just seemed to be all the way one way or all the way the other. i dont know if i need a higher rotation pot so i can be more accurate with it? im currently using something like a 300 degree at the moment
Title: Re: ionisiation?
Post by: dc42 on Dec 01, 2012, 07:48 pm
I really don't think you need an op amp for this. The Arduino pins have very high input resistance (around 100 Mohms), so detecting the difference between 1.7Mohms and infinity is easy. I used a voltage divider made from two 4.7Mohm resistors with an atmega328p in a recent project. However, you will need to take precautions against picking up interference. I suggest you connect your ionisation probe between the input pin and ground, use a 4.7Mohm pullup resistor to +5V, and also connect a 0.1uF capacitor between the input pin and ground.
Title: Re: ionisiation?
Post by: Grumpy_Mike on Dec 02, 2012, 10:05 am

right i tried that and it didnt seem to work when adjusting the pot it just seemed to be all the way one way or all the way the other. i dont know if i need a higher rotation pot so i can be more accurate with it? im currently using something like a 300 degree at the moment

You can get finer control by putting fixed resistors in the top and bottom of the pot so the wiper covers a smaller of voltages. Also try reducing the gain a bit.
Title: Re: ionisiation?
Post by: Joes on Dec 06, 2012, 06:59 pm
Quote
I really don't think you need an op amp for this. The Arduino pins have very high input resistance (around 100 Mohms), so detecting the difference between 1.7Mohms and infinity is easy. I used a voltage divider made from two 4.7Mohm resistors with an atmega328p in a recent project. However, you will need to take precautions against picking up interference. I suggest you connect your ionisation probe between the input pin and ground, use a 4.7Mohm pullup resistor to +5V, and also connect a 0.1uF capacitor between the input pin and ground.

i did try this but did not seem to work


Quote
You can get finer control by putting fixed resistors in the top and bottom of the pot so the wiper covers a smaller of voltages. Also try reducing the gain a bit


i haven't altered the gain at all, i presume to lower the gain i reduce the value size of the 100k which is connected to the output of the op amp?
right i think i've got it working in a matter of speaking with out altering the gain the problem i have now is it seems to be too sensitive still so putting my finger between the probes is enough to activate it.
Title: Re: ionisiation?
Post by: Grumpy_Mike on Dec 06, 2012, 09:14 pm
Quote
still so putting my finger between the probes is enough to activate it

That would be normal for a high gain high impedance circuit like you have here.