Although I give great credit to the RF idea, I'm not sure I want to introduce a high frequency RF signal in a metal chamber with a PCB of unknown design (the one being reflowed). Some chips may not like the absorbed power.
I also have the same apprehension with the spark idea. Introduction of a high voltage (even if contained) is not really something I think is a great idea. I do not knock the merit of the idea, just the introduction of that method may be a liability.
Because of the temperatures involved, there will only be a viewable spot from the top of the chamber. No side windows will exist. The chamber will be 10 inches deep and constructed of stainless steel.
I'm not sure what strange effects this would cause using a sonic type measurement. With a chamber 20 x 20 x 10 inches in area, the reflection may be a problem.
For a reference, the vapor layer is targeted to be 4 inches deep (total height), leaving a 6 inch area of safety to prevent vapor escape. The chamber will also be sealed with a top containing a glass that is rated high enough in case of an emergency. There will be a bleed tube (to prevent a pressure build up) which will have a condensing coil.
I think the brain storming is great, is shows there are a large number of folks that exercise their gray matter on a regular basis.
"I'm not sure what strange effects this would cause using a sonic type measurement. With a chamber 20 x 20 x 10 inches in area, the reflection may be a problem." - The "reflection" is the basis for the standing wave that would be created indicating that a resonant frequency had been reached.· This unique frequency not only depends on the dimensions of the container, but also the contents of the container. (fluid or gas density) ·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Beau Schwabe
IC Layout Engineer
Parallax, Inc.
While My idea of using RF at microwave levels might not be the best solution, It is connected and related
Assuming that a well built transmitter and receiver is in place across the vapor chamber. As the vapor is applied some of the RF signal will be absorbed by the vapor and another part of the signal will have its frequency changed by the Doppler effect or Doppler Shift. So this part of the signal is now at a different freq. and is not recognized by the receiver.
__________$WMc%___In memory or Christian Doppler__Austrian Physicist_1842___
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Truth is out there············································ BoogerWoods, FL. USA
I have a leak detector for refrigerant leaks in air-conditioning systems.· This uses an electronic sensor and has a little bit of electronics to create a pulse train whose frequency increases when R12 or R134a is present in the air surrounding the sensor.· It's very sensitive.· You listen to the pulse train on a little speaker, and when it sirens instead of clicking you've found the leak.· The whole thing was about eighty bucks new.
I have no idea how the sensor works or what it's made of, but perhaps there are, or can be, similar sensors that could work at your required temperatures and detect the vapors you need to detect.· Chemistry is magic.· Magic to me, anyway.
To discover whether something like this might work for you, a little research is in order.· Enjoy.
While My idea of using RF at microwave levels might not be the best solution, It is connected and related
Assuming that a well built transmitter and receiver is in place across the vapor chamber. As the vapor is applied some of the RF signal will be absorbed by the vapor and another part of the signal will have its frequency changed by the Doppler effect or Doppler Shift. So this part of the signal is now at a different freq. and is not recognized by the receiver.
__________$WMc%___In memory or Christian Doppler__Austrian Physicist_1842___
Doppler effect is a result of physical motion, a change in path length between transmitter and receiver.· Absorption is unrelated, as is any substance through which the signal happens to pass.
I don't quite understand why you think the frequency will change in passing through the vapor (or through anything else, either).· It won't, of course.· But we must not steal the thread.
since you want to maintain the temperature gradient on the board, wouldn't it be simplest to monitor the board temp and adjust the heating element output instead of worrying about vapor height?
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Parallax Forums - If you're ready to learn, we're ready to help.
James, just to clarify my suggestion of using heater wire, what I had in mind was measuring the change in resistance of the wire as the vapor height immersed more of the wire, not heating the wire up. What I pictured was winding several turns of fine wire around a mica sheet (somewhat like a toaster element) and standing it up in the enclosure. After looking at the web site you posted and reading the posts after my first suggestion however I do not think that would work unless you cooled the top portion of the element to produce a temperature gradient. I was expecting the air above the vapor to be cooler, and the resistance to change as the vapor rose and heated more and more of the element.
At this point I think the three viable options are the capacitance, ultrasonic, and optical methods.
For the capacitance method I would use two capacitors, one wide at the top and narrower at the bottom, and one the opposite so you could use them in a capacitance bridge style of circuit.
For an ultrasonic detector you would need one of the higher frequency ( 10+ MHz ) units used in medical ultrasound scanners to get the resolution you want.
The optical method may be the simplest and most reliable way to go if you use a standard video imaging chip to measure the demarcation point where the vapor condenses on the enclosure or a quartz window.
CJ said...
since you want to maintain the temperature gradient on the board, wouldn't it be simplest to monitor the board temp and adjust the heating element output instead of worrying about vapor height?
Well, possibly, but I'm worried about over run. Since the the board sized will fluctuate, without some knowledge of the vapor height, it would be easy to over temp the board at the very beginning of the process (exceed the 3 deg C/second). Larger panels wouldn't be so sensitive to being over ramped, but some of the smaller boards (as small as 2" square) will not be so impervious to over ramp.
I have just about come to the conclusion a thermocouple right below the board height is the easiest way to go, with possibly the capacitance method being a second.
I know the previous would probably be good enough, but I was looking for other options.
The process will be refined with time, because the knowledge of how fast the vapor will rise in the chamber will be learned. this will give an indication of height based on time and ambient temperature. An ambient temperature sensor will be on the control board.
Now the other question, of how much does the air in the chamber heat? That is one for testing I suppose.
If the sensor from Parallax will survive the temperature in the upper chamber it is going to get a workout from day to day, especially if we keep up the pace we have set for this week.
Just food for though, if anyone is interested in testing other methods, I would be willing to put any sensor in for the test.
It has been a very interesting discussion so far, and hope that people will keep thinking on the subject.
kwinn said...
James, just to clarify my suggestion of using heater wire, what I had in mind was measuring the change in resistance of the wire as the vapor height immersed more of the wire, not heating the wire up. What I pictured was winding several turns of fine wire around a mica sheet (somewhat like a toaster element) and standing it up in the enclosure. After looking at the web site you posted and reading the posts after my first suggestion however I do not think that would work unless you cooled the top portion of the element to produce a temperature gradient. I was expecting the air above the vapor to be cooler, and the resistance to change as the vapor rose and heated more and more of the element.
At this point I think the three viable options are the capacitance, ultrasonic, and optical methods.
For the capacitance method I would use two capacitors, one wide at the top and narrower at the bottom, and one the opposite so you could use them in a capacitance bridge style of circuit.
For an ultrasonic detector you would need one of the higher frequency ( 10+ MHz ) units used in medical ultrasound scanners to get the resolution you want.
The optical method may be the simplest and most reliable way to go if you use a standard video imaging chip to measure the demarcation point where the vapor condenses on the enclosure or a quartz window.
I understood the theory. The heating (or spread of heat) above the vapor was the point of concern. The upper portion of the wire could be connected to something that could help produce a heat gradient.
When the system is built, I will test a few different methods and report back my findings. It may be a good test bed for some different ideas.
You got Me again. I incorrectly fig. moving gas flow for "path length" whoops!!!
Last night or early this morning I was working on a CO,CO2 monitor for our C.E.M.S. at work.This gas Analyzer uses pulsed
I.R. light to detect CO and CO2. The I.R. is pulsed with a stepper driving chopper wheel at 200000kHz. As the concentration
of CO,CO2 increases the I.R. intensity decreases.
Zero Cal. gas is .05% CO,CO2 and the span gas bottle is 5.0% CO,CO2 . This is pretty tight on measuring a gas.
This might be useful in mearsuring the " VAPOR "
___________$WMc%___________
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Truth is out there············································ BoogerWoods, FL. USA
I've had to calibrate ultrasonic sensors that used a sound pulse to detect distance to a liquid level. Has this been ruled out as a solution? In my application foam on top of a liquid meant all bets were off.
Comments
I also have the same apprehension with the spark idea. Introduction of a high voltage (even if contained) is not really something I think is a great idea. I do not knock the merit of the idea, just the introduction of that method may be a liability.
Because of the temperatures involved, there will only be a viewable spot from the top of the chamber. No side windows will exist. The chamber will be 10 inches deep and constructed of stainless steel.
I'm not sure what strange effects this would cause using a sonic type measurement. With a chamber 20 x 20 x 10 inches in area, the reflection may be a problem.
For a reference, the vapor layer is targeted to be 4 inches deep (total height), leaving a 6 inch area of safety to prevent vapor escape. The chamber will also be sealed with a top containing a glass that is rated high enough in case of an emergency. There will be a bleed tube (to prevent a pressure build up) which will have a condensing coil.
I think the brain storming is great, is shows there are a large number of folks that exercise their gray matter on a regular basis.
James L
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
James L
Partner/Designer
Lil Brother SMT Assembly Services
"I'm not sure what strange effects this would cause using a sonic type measurement. With a chamber 20 x 20 x 10 inches in area, the reflection may be a problem." - The "reflection" is the basis for the standing wave that would be created indicating that a resonant frequency had been reached.· This unique frequency not only depends on the dimensions of the container, but also the contents of the container. (fluid or gas density)
·
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Beau Schwabe
IC Layout Engineer
Parallax, Inc.
While My idea of using RF at microwave levels might not be the best solution, It is connected and related
Assuming that a well built transmitter and receiver is in place across the vapor chamber. As the vapor is applied some of the RF signal will be absorbed by the vapor and another part of the signal will have its frequency changed by the Doppler effect or Doppler Shift. So this part of the signal is now at a different freq. and is not recognized by the receiver.
__________$WMc%___In memory or Christian Doppler__Austrian Physicist_1842___
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Truth is out there············································ BoogerWoods, FL. USA
I have a leak detector for refrigerant leaks in air-conditioning systems.· This uses an electronic sensor and has a little bit of electronics to create a pulse train whose frequency increases when R12 or R134a is present in the air surrounding the sensor.· It's very sensitive.· You listen to the pulse train on a little speaker, and when it sirens instead of clicking you've found the leak.· The whole thing was about eighty bucks new.
I have no idea how the sensor works or what it's made of, but perhaps there are, or can be, similar sensors that could work at your required temperatures and detect the vapors you need to detect.· Chemistry is magic.· Magic to me, anyway.
To discover whether something like this might work for you, a little research is in order.· Enjoy.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
· -- Carl, nn5i@arrl.net
I don't quite understand why you think the frequency will change in passing through the vapor (or through anything else, either).· It won't, of course.· But we must not steal the thread.
Cheers.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
· -- Carl, nn5i@arrl.net
Is a vapor moving through and chamber not physical motion?
____$WMc%_
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Truth is out there············································ BoogerWoods, FL. USA
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Parallax Forums - If you're ready to learn, we're ready to help.
At this point I think the three viable options are the capacitance, ultrasonic, and optical methods.
For the capacitance method I would use two capacitors, one wide at the top and narrower at the bottom, and one the opposite so you could use them in a capacitance bridge style of circuit.
For an ultrasonic detector you would need one of the higher frequency ( 10+ MHz ) units used in medical ultrasound scanners to get the resolution you want.
The optical method may be the simplest and most reliable way to go if you use a standard video imaging chip to measure the demarcation point where the vapor condenses on the enclosure or a quartz window.
Well, possibly, but I'm worried about over run. Since the the board sized will fluctuate, without some knowledge of the vapor height, it would be easy to over temp the board at the very beginning of the process (exceed the 3 deg C/second). Larger panels wouldn't be so sensitive to being over ramped, but some of the smaller boards (as small as 2" square) will not be so impervious to over ramp.
I have just about come to the conclusion a thermocouple right below the board height is the easiest way to go, with possibly the capacitance method being a second.
I know the previous would probably be good enough, but I was looking for other options.
The process will be refined with time, because the knowledge of how fast the vapor will rise in the chamber will be learned. this will give an indication of height based on time and ambient temperature. An ambient temperature sensor will be on the control board.
Now the other question, of how much does the air in the chamber heat? That is one for testing I suppose.
If the sensor from Parallax will survive the temperature in the upper chamber it is going to get a workout from day to day, especially if we keep up the pace we have set for this week.
Just food for though, if anyone is interested in testing other methods, I would be willing to put any sensor in for the test.
It has been a very interesting discussion so far, and hope that people will keep thinking on the subject.
James L
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
James L
Partner/Designer
Lil Brother SMT Assembly Services
Post Edited (James Long) : 3/23/2009 2:22:50 AM GMT
I understood the theory. The heating (or spread of heat) above the vapor was the point of concern. The upper portion of the wire could be connected to something that could help produce a heat gradient.
When the system is built, I will test a few different methods and report back my findings. It may be a good test bed for some different ideas.
James L
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
James L
Partner/Designer
Lil Brother SMT Assembly Services
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
· -- Carl, nn5i@arrl.net
Post Edited (Carl Hayes) : 3/23/2009 2:22:26 AM GMT
You got Me again. I incorrectly fig. moving gas flow for "path length" whoops!!!
Last night or early this morning I was working on a CO,CO2 monitor for our C.E.M.S. at work.This gas Analyzer uses pulsed
I.R. light to detect CO and CO2. The I.R. is pulsed with a stepper driving chopper wheel at 200000kHz. As the concentration
of CO,CO2 increases the I.R. intensity decreases.
Zero Cal. gas is .05% CO,CO2 and the span gas bottle is 5.0% CO,CO2 . This is pretty tight on measuring a gas.
This might be useful in mearsuring the " VAPOR "
___________$WMc%___________
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
The Truth is out there············································ BoogerWoods, FL. USA
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
· -- Carl, nn5i@arrl.net