It's labled MI or MT something. Looks like a mic to me...? What am I missing?
Snoredog
Blarg.
That is an output pressure transducer. It monitors the exit pressure of the air out and feeds directly into the electronics and software that control the brushless motor speed.
It is possible that it may also be used to monitor pressure oscillations that represent snore vibrations. But there is a technical difference between an audio device & a pressure device.
One reason I am aware of audio components is that early on in my life (when much younger) I worked as an audio engineer & did a spell working on the transistorized hearing aids. Audio detection devices are built very differently from pressure detection devices. Although in the very broad sense they both work on converting air pressure into electronic signals. The normal microphone has a broader frequency specialization than a pressure sensor which detects pressure variations at very low frequencies and using a different type of pressure pick up technique.
DSM
#2 Meant to include that when you run these things open like this you can play with the various pressure lines & learn what they do. I mentioned elsewhere that in one such test I hooked up the air exit pressure transducer of a Bipap Pro2 & Bipap S/T to the internal airline of my PB330 airhose. I was interested to see if the machine ran more accurately but instead, when I would stop breathing the mask went into pulsing gyrations - the pressure feedback was too quick & the machine was clearly tuned for a phase gap between pressure feedback & motor response. The smaller the mask, the faster it pulsed in this situation. It was quite funny at the time .
That is an output pressure transducer. It monitors the exit pressure of the air out and feeds directly into the electronics and software that control the brushless motor speed.
It is possible that it may also be used to monitor pressure oscillations that represent snore vibrations. But there is a technical difference between an audio device & a pressure device.
One reason I am aware of audio components is that early on in my life (when much younger) I worked as an audio engineer & did a spell working on the transistorized hearing aids. Audio detection devices are built very differently from pressure detection devices. Although in the very broad sense they both work on converting air pressure into electronic signals. The normal microphone has a broader frequency specialization than a pressure sensor which detects pressure variations at very low frequencies and using a different type of pressure pick up technique.
DSM
#2 Meant to include that when you run these things open like this you can play with the various pressure lines & learn what they do. I mentioned elsewhere that in one such test I hooked up the air exit pressure transducer of a Bipap Pro2 & Bipap S/T to the internal airline of my PB330 airhose. I was interested to see if the machine ran more accurately but instead, when I would stop breathing the mask went into pulsing gyrations - the pressure feedback was too quick & the machine was clearly tuned for a phase gap between pressure feedback & motor response. The smaller the mask, the faster it pulsed in this situation. It was quite funny at the time .
xPAP and Quattro std mask (plus a pad-a-cheek anti-leak strap)
these machines (pretty much all of them) measure at a minimum, 2 main characteristics: Volume FLOW and PRESSURE, they are two different things. For that they use 2 separate circuits found on nearly all xpaps.dsm wrote:Snores,
Take a look at these photos, these are not microphones. They are pressure
The device that has 2 tubes coming off it is generally the device that measures FLOW. The second device with single (1) tube terminating on the PCB mounted transducer is the pressure/snore sensor circuit.
Since you don't have a picture of it out of the chassis, looking at the above picture and seeing the honeycomb like grate (inside the outlet, very hard to see) in the outlet port, I'd say that is a Mass Air flow (MAF) sensor with possibly a tiny thermistor on the other side if that truly is a MAF device, a thermistor should be suspended in the the center by 1 or 2 wires, may even be 2 tiny thermistors suspended in the center, the same thing found on the Remstar device in picture (below).
The purpose of the grate is to smooth out the airflow over the thermistor for more accurate readings. But that would be a bit surprising to see in a Resmed machine since Sullivan is on record with his dislike of thermistors and their accuracy. They could have also used a tiny pitot-type tube inside to measure differential flow (where the 2 tubes terminate on the PCB on both machines).
On a Remstar, this device below (MAF) measures the FLOW in the circuit:
On a Remstar, this transducer device (black device on PCB where single tube terminates) measures the pressure in the circuit and snores functioning as a mic:
If you disconnect that single tube/hose the motor should rev up and the machine should shut off most likely with an error. This is the same circuit found on a 420e where the tiny pressure tube inside the hose terminates to a transducer on the inside. The 420e uses a pneumotach sensor to detect flow and cardiac oscillations. Remstar and Resmed and others did away with the separate pressure sensor hose. IF you KNOW the hose to be used is 6ft long you can factor out the loss in the hose (Resmed ASKS for length of hose from the Clinical menu on their machines). So putting your diffuser in-circuit may not be so wise after all, reason testing is needed.
Mass Air flow (MAF) sensor measures the FLOW through the machine as you breathe in/out, it is how it detects an apnea, it measures the differential pressure changes between those 2 tubes which also terminates to the main PCB on both machines. As the air flows past those 2 tubes or MAF device the differential pressure is measured to obtain the velocity pressure where they are converted to electrical signals with a dual transducer. From that they can determine volume flow as you breathe in/out or have an apnea.
The pressure transducer seen on Resmed and similar to the Remstar is used to measure pressure/snore (and yes it is a mic) is shown below with tube:
The device measures the pressure changes in amplitude such as those changes seen with snore[/i] (reason they are on the same transducer).
consult with the ResCare Patent 5245995, Fig. 10, 11 & 12, more specifically Fig. 13 drawing (think it is on page 11) will show you the schematic of how they measure for snore frequency (fig. 10-12 show it in circuit).
SWS: I don't think they use those pneumotacographic sensors found in a critical care neonatal unit in these $500 machines, I don't know, could be wrong?
I would think that would be almost cost prohibitive to find in these machines (maybe the higher end ASV versions). Maybe they use some cheaper form of one.
someday science will catch up to what I'm saying...
It seems we are really boiling this down to tech terminology.
As a former Audio engineer, I believe the use of the term mic here is misleading.
In one sense it is like saying a truck and a passenger car are both automobiles. In a broad sense that is sort of true but to an auto engineer it is not a very accurate description of one versus the other.
But the point here is we all all in agreement (I believe) that the exit pressure transducer measures both exit air pressure and air vibrations that are created by snores.
To say that the exit air pressure transducer measures sound, is to me inaccurate. This is where we perhaps differ over the device being a 'pressure' transducer vs an audio 'mic' (a truck or a sedan).
In the broader scheme of things it probably doesn't matter.
D
As a former Audio engineer, I believe the use of the term mic here is misleading.
In one sense it is like saying a truck and a passenger car are both automobiles. In a broad sense that is sort of true but to an auto engineer it is not a very accurate description of one versus the other.
But the point here is we all all in agreement (I believe) that the exit pressure transducer measures both exit air pressure and air vibrations that are created by snores.
To say that the exit air pressure transducer measures sound, is to me inaccurate. This is where we perhaps differ over the device being a 'pressure' transducer vs an audio 'mic' (a truck or a sedan).
In the broader scheme of things it probably doesn't matter.
D
xPAP and Quattro std mask (plus a pad-a-cheek anti-leak strap)
PS - Snores
The thermistor used in the fan housing is there as a temperature overload device. It serves no other purpose other than to shut down the xPAP should the motor fail in a way that createss heat. Thermistor means thermal resistor - varies resistance based on temperature.
So if the motor were to overheat (electronic failure, fan jam etc:) the machine *does not want to* allow heated air to find its way to the user. It shuts down. *If* it has a thermistor protection circuit.
D
The thermistor used in the fan housing is there as a temperature overload device. It serves no other purpose other than to shut down the xPAP should the motor fail in a way that createss heat. Thermistor means thermal resistor - varies resistance based on temperature.
So if the motor were to overheat (electronic failure, fan jam etc:) the machine *does not want to* allow heated air to find its way to the user. It shuts down. *If* it has a thermistor protection circuit.
D
xPAP and Quattro std mask (plus a pad-a-cheek anti-leak strap)
[quote="dsm"]It seems we are really boiling this down to tech terminology.
As a former Audio engineer, I believe the use of the term mic here is misleading.
In one sense it is like saying a truck and a passenger car are both automobiles. In a broad sense that is sort of true but to an auto engineer it is not a very accurate description of one versus the other.
But the point here is we all all in agreement (I believe) that the exit pressure transducer measures both exit air pressure and air vibrations that are created by snores.
To say that the exit air pressure transducer measures sound, is to me inaccurate. This is where we perhaps differ over the device being a 'pressure' transducer vs an audio 'mic' (a truck or a sedan).
In the broader scheme of things it probably doesn't matter.
D
As a former Audio engineer, I believe the use of the term mic here is misleading.
In one sense it is like saying a truck and a passenger car are both automobiles. In a broad sense that is sort of true but to an auto engineer it is not a very accurate description of one versus the other.
But the point here is we all all in agreement (I believe) that the exit pressure transducer measures both exit air pressure and air vibrations that are created by snores.
To say that the exit air pressure transducer measures sound, is to me inaccurate. This is where we perhaps differ over the device being a 'pressure' transducer vs an audio 'mic' (a truck or a sedan).
In the broader scheme of things it probably doesn't matter.
D
someday science will catch up to what I'm saying...
well pull the hose off that thermal device and see what happens to the pressure.dsm wrote:PS - Snores
The thermistor used in the fan housing is there as a temperature overload device. It serves no other purpose other than to shut down the xPAP should the motor fail in a way that createss heat. Thermistor means thermal resistor - varies resistance based on temperature.
So if the motor were to overheat (electronic failure, fan jam etc:) the machine *does not want to* allow heated air to find its way to the user. It shuts down. *If* it has a thermistor protection circuit.
D
It may go nuclear on you so wear a vest.
someday science will catch up to what I'm saying...
Snores,
Again, we are heading down the same track
Actually, most modern mics (except some very expensive models) use a piezo electric crystal to convert sound to electrical energy. As you pointed out - using the principles of a speaker cone (but more flattened as in a diaphram).
Pressure sensors also use piezoelectric devices but constructed in a quite different way from a sound detector.
Here is one example of heavy duty piezoelectric pressure sensors. But these bear little resemblance to a mic.
http://www.davidson.com.au/products/pre ... theory.asp
I may find a diagram of the actual chips used in the xPAPs shown.
D
Again, we are heading down the same track
Actually, most modern mics (except some very expensive models) use a piezo electric crystal to convert sound to electrical energy. As you pointed out - using the principles of a speaker cone (but more flattened as in a diaphram).
Pressure sensors also use piezoelectric devices but constructed in a quite different way from a sound detector.
Here is one example of heavy duty piezoelectric pressure sensors. But these bear little resemblance to a mic.
http://www.davidson.com.au/products/pre ... theory.asp
I may find a diagram of the actual chips used in the xPAPs shown.
D
xPAP and Quattro std mask (plus a pad-a-cheek anti-leak strap)
trust me, I will FIND the actual Resmed document where they refer to the "MIC" and pressure transducer being of the same thing and I'll put it on-line, I only have about a thousand documents to search through but I read it a few weeks back.dsm wrote:Snores,
Again, we are heading down the same track
Actually, most modern mics (except some very expensive models) use a piezo electric crystal to convert sound to electrical energy. As you pointed out - using the principles of a speaker cone (but more flattened as in a diaphram).
Pressure sensors also use piezoelectric devices but constructed in a quite different way from a sound detector.
Here is one example of heavy duty piezoelectric pressure sensors. But these bear little resemblance to a mic.
http://www.davidson.com.au/products/pre ... theory.asp
I may find a diagram of the actual chips used in the xPAPs shown.
D
Here is what another statement from the Resmed Clinical Manual, 30846, page 9:
The Flattening Index is a measure of silent inspiratory airflow limitation. Flow limitation with loud snoring is handled by the snore detector. When a patient snores, sound is generated and the inspiratory flow/time curve is distorted by the frequency of the sound.
someday science will catch up to what I'm saying...
DSM, you seem to be saying that pressure sensors are different from mics because they measure outside the typical frequencies we consider sound. That's all fine and dandy.
I guess I'm just confused as to why they'd need to measure outside sound frequencies when detecting snores, because we hear them....
I guess I'm just confused as to why they'd need to measure outside sound frequencies when detecting snores, because we hear them....
I'm a programmer Jim, not a doctor!
Snoredog, that screen grating is, indeed, to straighten out turbulence. The MAS (Mass Airflow Sensor) pictured is a type of pneumotachograph (not a thermistor).
Doug, think of this turbulence as "micro-turbulence" if you may, but turbulence is a bona fide flow-measurement issue when differential pressure is being measured across multiple or "bundled" sensor heads that are incredibly tiny and within close proximity.
Anything accoustic (i.e. snore) is generally transduced via pressure transducer. However, supplementary snore information is sitting in the flow signal as well, and is processed. Snore is but a particle-movement-based pressure wave. Right? That's a job primarily for a pressure transducer. Airflow is a "mass" or "volume" movement of gas. That's a job for a flow sensor.
Snoredog, a thermistor relies on human breath to change resistance. The varying voltage across that varying resistance is in turn measured, from which flow is indirectly derived. Thermistors are generally not as accurate as pneumotachographs. Even the original Autoset used a pneumotachograph---but not the more sensitive bundled capillary/tube type. It used a paddle-actuated sensor that even qualifies as pneumotach rather than thermistor. There are several pneumotach sensor types, all of which measure pressure-differential-based flow rather than varying-resistance-based flow (thermistor).
Great, great round of posts guys. Thank you SO much!!!!!!!
P.S. Any microphone element is a pressure transducer. And various pressure transducer types can be used as microphones. The APAP pressure transducer pulls double-duty, and thus functionally qualifies as a microphone in my opinion. I agree that we're hair splitting on that one, though.
Doug, think of this turbulence as "micro-turbulence" if you may, but turbulence is a bona fide flow-measurement issue when differential pressure is being measured across multiple or "bundled" sensor heads that are incredibly tiny and within close proximity.
Anything accoustic (i.e. snore) is generally transduced via pressure transducer. However, supplementary snore information is sitting in the flow signal as well, and is processed. Snore is but a particle-movement-based pressure wave. Right? That's a job primarily for a pressure transducer. Airflow is a "mass" or "volume" movement of gas. That's a job for a flow sensor.
Snoredog, a thermistor relies on human breath to change resistance. The varying voltage across that varying resistance is in turn measured, from which flow is indirectly derived. Thermistors are generally not as accurate as pneumotachographs. Even the original Autoset used a pneumotachograph---but not the more sensitive bundled capillary/tube type. It used a paddle-actuated sensor that even qualifies as pneumotach rather than thermistor. There are several pneumotach sensor types, all of which measure pressure-differential-based flow rather than varying-resistance-based flow (thermistor).
Great, great round of posts guys. Thank you SO much!!!!!!!
P.S. Any microphone element is a pressure transducer. And various pressure transducer types can be used as microphones. The APAP pressure transducer pulls double-duty, and thus functionally qualifies as a microphone in my opinion. I agree that we're hair splitting on that one, though.
Last edited by -SWS on Wed Apr 11, 2007 9:00 pm, edited 2 times in total.
Snoredog wrote:trust me, I will FIND the actual Resmed document where they refer to the "MIC" and pressure transducer being of the same thing and I'll put it on-line, I only have about a thousand documents to search through but I read it a few weeks back.dsm wrote:Snores,
Again, we are heading down the same track
Actually, most modern mics (except some very expensive models) use a piezo electric crystal to convert sound to electrical energy. As you pointed out - using the principles of a speaker cone (but more flattened as in a diaphram).
Pressure sensors also use piezoelectric devices but constructed in a quite different way from a sound detector.
Here is one example of heavy duty piezoelectric pressure sensors. But these bear little resemblance to a mic.
http://www.davidson.com.au/products/pre ... theory.asp
I may find a diagram of the actual chips used in the xPAPs shown.
D
Here is what another statement from the Resmed Clinical Manual, 30846, page 9:The Flattening Index is a measure of silent inspiratory airflow limitation. Flow limitation with loud snoring is handled by the snore detector. When a patient snores, sound is generated and the inspiratory flow/time curve is distorted by the frequency of the sound.
xPAP and Quattro std mask (plus a pad-a-cheek anti-leak strap)
Ok, we're hair splitting, but at least now I see why. Mics don't measure anything. They convert pressure modulations to electricity. The computer or DSP or whatever the mic is plugged into can measure all it wants, but that's why we're going down this path.dsm wrote:Mics are devices that measure sound in decibels (not pressure).
Anyway, thanks for increasing my understanding of what's going on here, and I don't care what you call it anymore.
I'm a programmer Jim, not a doctor!
Found this - getting closer to the actual ones in the xPAPs.
DSM
http://www.sensortechnics.com/index.php ... 2659e14523
Aha! - from the above site - 'flow sensors' - these look familiar.
http://www.sensortechnics.com/index.php ... 968983c896
Now to look for a straight pressure sensor as used.
Found !
http://www.sensortechnics.com/index.php ... ba0fab1cef
D
DSM
http://www.sensortechnics.com/index.php ... 2659e14523
Aha! - from the above site - 'flow sensors' - these look familiar.
http://www.sensortechnics.com/index.php ... 968983c896
Now to look for a straight pressure sensor as used.
Found !
http://www.sensortechnics.com/index.php ... ba0fab1cef
D
Last edited by dsm on Wed Apr 11, 2007 9:33 pm, edited 2 times in total.
xPAP and Quattro std mask (plus a pad-a-cheek anti-leak strap)
that is because the airflow is looked at (by the machine algorithm) as a sine wave like you would see on an oscilloscope. The breath or flow is monitored by assigning numeric values to those waveforms (like shown in the center blue line in the various forms of SDB events below).blarg wrote:DSM, you seem to be saying that pressure sensors are different from mics because they measure outside the typical frequencies we consider sound. That's all fine and dandy.
I guess I'm just confused as to why they'd need to measure outside sound frequencies when detecting snores, because we hear them....
That center blue line below might as well be voltage signals as the line goes up so does the voltage, so when it sees the up and down waveform like from a snore (center right) it sees the voltage go up and down in rapid frequency (could as easily be resistance it doesn't really matter). it is how it sees and determines a snore. Snore is easy to spot compared to the other events. A Hypopnea would appear the same as Flow Limitation.
I don't have a problem with the hardware technology used on Resmed, I just don't care for its snore response in the A10 algorithm. If you snore and it increases pressure to eliminate said snore, then it can take it 20-minutes for the pressure to drop back down again. In fact for most events it can take 20-minutes for the pressure to settle back down period (lets see if you have 3 events per hour, 3x20=60, pressure may not ever drop). That means if I have a central as a result of existing pressure like from snore it can take the machine 20 minutes to drop back down.
A 420e can increase eliminate the event and drop back down in only a few minutes, if it sees a CA it drops immediately. The Remstar's snore response is limited, if it doesn't knock out the snore it stops after 3 pressure increases and locks itself out. The main argument is if you increase/decrease pressure too rapidly it may trigger an arousal or wake you.
someday science will catch up to what I'm saying...