Re: ResMed S9 coming soon?
Posted: Wed Feb 10, 2010 10:09 pm
Uncle Bob, if you end up having problems hosting those documents, I have room on the Lionlamb.us server.
DSM, I am going to take you up on trying to explain the ResMed patent claims. In order to do this though, I am going to have to give an 'introduction to AC electronics' course, and show how the concepts relate to a breathing system augmented by xPAP. I will do this in two, and maybe 3 posts. The first 1 or 2 will define what AC electronics is, and define terms. The third will take what was learned in the first post(s) and apply it to the ResMed patent. So, here goes!
I know some of you here are familiar with Ohm's law, which relates how voltage, current, and resistance (and by derivation, power) interact. You will see this discussed occasionally on posts about power. Ohm's law is primarily for direct current (DC) circuits like you have with battery power. AC electronics attempts to do the same thing, but with alternating current (AC). AC electronics is of special importance to my career, as it describes how things like radio transmitters and receivers work. It is also important to AC power distribution, and relates to discussions about inverters, etc. The field of AC electronics exists largely due to the efforts of a gentleman named Charles Steinmetz, who is basically the person who made General Electric what it is today.
DC is a steady flow of an electric current in a circuit, like what you get from a battery. AC current is a constantly varying current that flows in one direction, and then the other. In many applications, the change in flow follows a smooth curve (referred to as a 'waveform') that we call a sine wave. However, AC does not have to be a sine wave. it can have a very irregular, or even square waveform. In breathing terminology, our breath cycle is like, a very irregular, nonsinusodal AC waveform.
In a DC circuit, there is a quantity called 'resistance' that resists the flow of current. Resistance also works in AC circuits, but there are some additional and very important additional things that work against current flow. These same items are key to understanding what happens in a breathing circuit as well.
I am sure you have all heard of a capacitor. A capacitor in its simplest form, is two conductive plates separated by an insulating material. If you connect a battery to a capacitor, current flows just long enough to charge the capacitor's plates to the same voltage as the battery. After that, no current flows. You can then disconnect the battery, and the capacitor will store the charge on its plates. This is why high voltage capacitors can be dangerous to handle, even if the power has been removed. The amount of charge that can be stored in a capacitor is called its 'capacitance'. The unit of capacitance is the 'Farad'.
Now, if you connect an AC voltage to a capacitor, the constantly changing voltage across the plates causes the capacitor to alternately charge discharge, and then charge in the opposite polarity, and so on. As a result, if averaged over time, the constant charging and discharging gives an appearance to the external circuit that current is actually flowing through the capacitor. This current can be easily measured with an AC ammeter.
If you raise the frequency of the AC, the charging and discharging of the capacitor's plates takes place faster, and it appears more current is flowing through the capacitor. The higher the frequency, the greater the current. Since no current can actually flow through the capacitor, this current flow is not caused by resistance. therefore, it is called 'reactance'. In the case of a capacitor, it is called 'capacitive reactance'. Reactance is given in ohms, just like resistance.
When the Ac first starts to charge a capacitor, the most current flows, even though the voltage is fairly low. As the AC voltage in the cycle increases, the capacitor is more and more charged, and the charging current decreases. By the time the AC waveform reaches its peak voltage, the capacitor is charged, and current flow is minimal. (I am simplifying this somewhat!) In any case, when capacitive reactance dominates an AC circuit, it is said the 'current flow leads the voltage'. We will see later how this also applies to a set of lungs.
The opposite of a capacitor is a coil of wire. More mysterious to the uninitiated, a coil of wire can store energy.
Whenever current flows in a conductor, it develops a magnetic field around the conductor. If you now wrap that conductor into a coil with many turns, the magnetic field is intensified by the increased number of turns. The amount that this magnetic field is concentrated by a coil of given dimensions and number of turns is called 'inductance'. The unit of inductance is the 'Henry'.
If you have a steady DC current flowing through a coil of wire, the current flow is limited only by the resistance of the wire. The magnetic field is steady, and we can do things with it, like pick up scrap metal. But if the magnetic field changes (either increase or decrease), the changing magnetic field lines 'cut across' the conductor, and induce a voltage in it. If you change the current flow through the coil, the magnetic field changes, and cuts the coil's windings. The voltage induced tends to oppose the change in the current flow. So, if the current flow is increasing, the induced 'back electromotive force or back EMF' tries to reduce the current flow. If the current flow is decreasing, the back EMF tries to increase it. If you remove the DC power from a large coil, the back EMF causes a very large voltage to momentarily appear across the coil, which is called an 'inductive kick'. This is why switches sometimes arc when you disconnect the power from a large inductive load like a motor.
Now, if you apply AC to a coil, the back EMF is trying to fight the flow of the AC current through the coil. As a result, less net current will flow through the coil than would for the same voltage of DC. The higher in frequency you go with the AC, the more pronounced the back EMF effect becomes, and the less current flows. Like in the case of the capacitor, this non-resistive impediment to the flow of current is called 'reactance', and the coil version is called 'inductive reactance'.
Now, if you apply an AC voltage to a coil, the back EMF will oppose the flow of current quite strongly, and little current flows. But as the voltage of the AC waveform approaches maximum, the magnetic field is changing at an ever slower rate. Less back EMF is generated, and more current flows. If the voltage stops changing at this point, the current flow will be limited only by the resistance of the wire in the coil. Thus in the case of the coil or 'inductor' as they are often called, the 'current flow lags the voltage'.
The resistance of a purely resistive element of an AC circuit does not change its resistance as AC frequency is changed. The current flow is always in step with the voltage. Thus the current neither leads or lags the voltage, and they are said to be 'in phase' with each other.
In the case of a coil or capacitor, with a sine wave AC applied to them, the current either leads or lags by 1/4 of a cycle, or 90 degrees. A pure reactance like this is said to have the current lead or lag in phase by 90 degrees.
Now, if you think of a circuit with, say a resistor and a capacitor in series in it, you can represent the resistance by the horizontal leg of a right triangle, which has a horizontal and vertical sides around the right angle. The capacitive reactance would be the vertical leg. In drawing these diagrams, the vertical leg is normally drawn going upwards from the right angle if the reactance is inductive. If the reactance is capacitive, the vertical leg goes down from the right angle. If a circuit contains both a coil and a capacitor along with the resistor (all circuits have some resistance), the values of their reactances cancel, and the length vertical leg of the triangle is the larger reactance minus the smaller reactance. The leg faces up or down based on the larger reactance. I am taking the time to explain this triangle concept because it will help you understand 'complex numbers'. impedance and admittance.
Once you have drawn the legs of your triangle, you can draw the hypotenuse of the triangle. The hypotenuse represents the 'impedance' of this circuit, and is calculated using the pythagorean therom. Thus, if you have a resistance of 3 ohms, and a reactance of 3 ohms, the impedance will be SQRT(3^2 + 3^2), or about 4.2 ohms.
Related to all this but part of another total discussion in another topic: The cosine of the angle on the resistance end of the hypotenuse is referred to as the 'power factor'. In a circuit where there is no reactance, the angle here would be 0 degrees. The cosine of zero is 1, so the power factor is 'unity'. Voltage and current are in phase. As resistance decreases and reactance increases, this angle would be sharper and sharper, being 90 degrees in a circuit that has all reactance and no resistance. In this case, the cosine of 90 degrees is 0, so the power factor would be zero (All the current flow is 'imaginary', as described below). Current will lead or lag voltage by 90 degrees depending on whether the reactance is capacitive or inductive.
In general, the higher the impedance, the less AC current flows in the circuit. However in some cases, you are interested in looking at a situation from a viewpoint that 'the less the impedance, the greater the current flow'. In those cases, you use the reciprocal of impedance, which is called 'admittance'. Thus, a smaller impedance would be a larger admittence, and vice versa. In the case of this patent, a greater admittance means more air flowing in and out of the lungs.
Now, impedance by itself does not tell you whether the reactive component is inductive or capacitive. There is another concept, called a 'complex' number' that is used to express impedance in cases where the magnitude and type of reactance needs to be known. A complex number has a 'real part' and an 'imaginary part' (which is beyond the scope of this discussion). The imaginary part of a complex number is prepended by a lowercase J. The sign of the imaginary part of the number indicates whether the net reactance is inductive (positive) or capacitive (negative), just like the vertical leg of the triangle described earlier. The real part of a complex impedance value is the resistive part. the imaginary part is the reactance, with the sign explained as above. (The reactance is considered 'imaginary' because the energy used in the reactive portion is returned to the circuit later in each cycle, and therefore doesn't really 'exist'.) For example, if an AC circuit has a resistive component of 8 ohms, and a capacitvely reactive part of 6 ohms, it would expressed like this: 8-j6 ohms. This is important to understand, as the algorithm in the ResMed patent separates the real and imaginary parts in the process of determining if the airway is open.
Now, if I haven't lost you completely, we are ready to look at the patent.
DSM, I am going to take you up on trying to explain the ResMed patent claims. In order to do this though, I am going to have to give an 'introduction to AC electronics' course, and show how the concepts relate to a breathing system augmented by xPAP. I will do this in two, and maybe 3 posts. The first 1 or 2 will define what AC electronics is, and define terms. The third will take what was learned in the first post(s) and apply it to the ResMed patent. So, here goes!
I know some of you here are familiar with Ohm's law, which relates how voltage, current, and resistance (and by derivation, power) interact. You will see this discussed occasionally on posts about power. Ohm's law is primarily for direct current (DC) circuits like you have with battery power. AC electronics attempts to do the same thing, but with alternating current (AC). AC electronics is of special importance to my career, as it describes how things like radio transmitters and receivers work. It is also important to AC power distribution, and relates to discussions about inverters, etc. The field of AC electronics exists largely due to the efforts of a gentleman named Charles Steinmetz, who is basically the person who made General Electric what it is today.
DC is a steady flow of an electric current in a circuit, like what you get from a battery. AC current is a constantly varying current that flows in one direction, and then the other. In many applications, the change in flow follows a smooth curve (referred to as a 'waveform') that we call a sine wave. However, AC does not have to be a sine wave. it can have a very irregular, or even square waveform. In breathing terminology, our breath cycle is like, a very irregular, nonsinusodal AC waveform.
In a DC circuit, there is a quantity called 'resistance' that resists the flow of current. Resistance also works in AC circuits, but there are some additional and very important additional things that work against current flow. These same items are key to understanding what happens in a breathing circuit as well.
I am sure you have all heard of a capacitor. A capacitor in its simplest form, is two conductive plates separated by an insulating material. If you connect a battery to a capacitor, current flows just long enough to charge the capacitor's plates to the same voltage as the battery. After that, no current flows. You can then disconnect the battery, and the capacitor will store the charge on its plates. This is why high voltage capacitors can be dangerous to handle, even if the power has been removed. The amount of charge that can be stored in a capacitor is called its 'capacitance'. The unit of capacitance is the 'Farad'.
Now, if you connect an AC voltage to a capacitor, the constantly changing voltage across the plates causes the capacitor to alternately charge discharge, and then charge in the opposite polarity, and so on. As a result, if averaged over time, the constant charging and discharging gives an appearance to the external circuit that current is actually flowing through the capacitor. This current can be easily measured with an AC ammeter.
If you raise the frequency of the AC, the charging and discharging of the capacitor's plates takes place faster, and it appears more current is flowing through the capacitor. The higher the frequency, the greater the current. Since no current can actually flow through the capacitor, this current flow is not caused by resistance. therefore, it is called 'reactance'. In the case of a capacitor, it is called 'capacitive reactance'. Reactance is given in ohms, just like resistance.
When the Ac first starts to charge a capacitor, the most current flows, even though the voltage is fairly low. As the AC voltage in the cycle increases, the capacitor is more and more charged, and the charging current decreases. By the time the AC waveform reaches its peak voltage, the capacitor is charged, and current flow is minimal. (I am simplifying this somewhat!) In any case, when capacitive reactance dominates an AC circuit, it is said the 'current flow leads the voltage'. We will see later how this also applies to a set of lungs.
The opposite of a capacitor is a coil of wire. More mysterious to the uninitiated, a coil of wire can store energy.
Whenever current flows in a conductor, it develops a magnetic field around the conductor. If you now wrap that conductor into a coil with many turns, the magnetic field is intensified by the increased number of turns. The amount that this magnetic field is concentrated by a coil of given dimensions and number of turns is called 'inductance'. The unit of inductance is the 'Henry'.
If you have a steady DC current flowing through a coil of wire, the current flow is limited only by the resistance of the wire. The magnetic field is steady, and we can do things with it, like pick up scrap metal. But if the magnetic field changes (either increase or decrease), the changing magnetic field lines 'cut across' the conductor, and induce a voltage in it. If you change the current flow through the coil, the magnetic field changes, and cuts the coil's windings. The voltage induced tends to oppose the change in the current flow. So, if the current flow is increasing, the induced 'back electromotive force or back EMF' tries to reduce the current flow. If the current flow is decreasing, the back EMF tries to increase it. If you remove the DC power from a large coil, the back EMF causes a very large voltage to momentarily appear across the coil, which is called an 'inductive kick'. This is why switches sometimes arc when you disconnect the power from a large inductive load like a motor.
Now, if you apply AC to a coil, the back EMF is trying to fight the flow of the AC current through the coil. As a result, less net current will flow through the coil than would for the same voltage of DC. The higher in frequency you go with the AC, the more pronounced the back EMF effect becomes, and the less current flows. Like in the case of the capacitor, this non-resistive impediment to the flow of current is called 'reactance', and the coil version is called 'inductive reactance'.
Now, if you apply an AC voltage to a coil, the back EMF will oppose the flow of current quite strongly, and little current flows. But as the voltage of the AC waveform approaches maximum, the magnetic field is changing at an ever slower rate. Less back EMF is generated, and more current flows. If the voltage stops changing at this point, the current flow will be limited only by the resistance of the wire in the coil. Thus in the case of the coil or 'inductor' as they are often called, the 'current flow lags the voltage'.
The resistance of a purely resistive element of an AC circuit does not change its resistance as AC frequency is changed. The current flow is always in step with the voltage. Thus the current neither leads or lags the voltage, and they are said to be 'in phase' with each other.
In the case of a coil or capacitor, with a sine wave AC applied to them, the current either leads or lags by 1/4 of a cycle, or 90 degrees. A pure reactance like this is said to have the current lead or lag in phase by 90 degrees.
Now, if you think of a circuit with, say a resistor and a capacitor in series in it, you can represent the resistance by the horizontal leg of a right triangle, which has a horizontal and vertical sides around the right angle. The capacitive reactance would be the vertical leg. In drawing these diagrams, the vertical leg is normally drawn going upwards from the right angle if the reactance is inductive. If the reactance is capacitive, the vertical leg goes down from the right angle. If a circuit contains both a coil and a capacitor along with the resistor (all circuits have some resistance), the values of their reactances cancel, and the length vertical leg of the triangle is the larger reactance minus the smaller reactance. The leg faces up or down based on the larger reactance. I am taking the time to explain this triangle concept because it will help you understand 'complex numbers'. impedance and admittance.
Once you have drawn the legs of your triangle, you can draw the hypotenuse of the triangle. The hypotenuse represents the 'impedance' of this circuit, and is calculated using the pythagorean therom. Thus, if you have a resistance of 3 ohms, and a reactance of 3 ohms, the impedance will be SQRT(3^2 + 3^2), or about 4.2 ohms.
Related to all this but part of another total discussion in another topic: The cosine of the angle on the resistance end of the hypotenuse is referred to as the 'power factor'. In a circuit where there is no reactance, the angle here would be 0 degrees. The cosine of zero is 1, so the power factor is 'unity'. Voltage and current are in phase. As resistance decreases and reactance increases, this angle would be sharper and sharper, being 90 degrees in a circuit that has all reactance and no resistance. In this case, the cosine of 90 degrees is 0, so the power factor would be zero (All the current flow is 'imaginary', as described below). Current will lead or lag voltage by 90 degrees depending on whether the reactance is capacitive or inductive.
In general, the higher the impedance, the less AC current flows in the circuit. However in some cases, you are interested in looking at a situation from a viewpoint that 'the less the impedance, the greater the current flow'. In those cases, you use the reciprocal of impedance, which is called 'admittance'. Thus, a smaller impedance would be a larger admittence, and vice versa. In the case of this patent, a greater admittance means more air flowing in and out of the lungs.
Now, impedance by itself does not tell you whether the reactive component is inductive or capacitive. There is another concept, called a 'complex' number' that is used to express impedance in cases where the magnitude and type of reactance needs to be known. A complex number has a 'real part' and an 'imaginary part' (which is beyond the scope of this discussion). The imaginary part of a complex number is prepended by a lowercase J. The sign of the imaginary part of the number indicates whether the net reactance is inductive (positive) or capacitive (negative), just like the vertical leg of the triangle described earlier. The real part of a complex impedance value is the resistive part. the imaginary part is the reactance, with the sign explained as above. (The reactance is considered 'imaginary' because the energy used in the reactive portion is returned to the circuit later in each cycle, and therefore doesn't really 'exist'.) For example, if an AC circuit has a resistive component of 8 ohms, and a capacitvely reactive part of 6 ohms, it would expressed like this: 8-j6 ohms. This is important to understand, as the algorithm in the ResMed patent separates the real and imaginary parts in the process of determining if the airway is open.
Now, if I haven't lost you completely, we are ready to look at the patent.
