Impedance a computation of information
Now almost all of this information is bits and pieces of work and definitions that I have gathered.
Although they are my thoughts I am not taking credit for this, I am just trying to help explain it as deep as I can
How I got started on this subject!
So here it goes
I stopped one of my workmates who was taking his CTS class and asked how he was doing
Not good, he was trying to understand impedance and asked what meter do I use to measure impedance.
I simply looked at the formula and said it’s not that easy
I asked if he understood inductance , he didn’t
As the conversation got longer it got harder
Finally I went to ohms law,
And started from scratch
From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Part of a series of articles about
Electromagnetism
• Electricity
• Magnetism
Electrostatics[show]
Magnetostatics[show]
Electrodynamics[show]
Electrical network[hide]
• Alternating current
• Capacitance
• Direct current
• Electric current
• Electric potential
• Electromotive force
• Impedance
• Inductance
• Ohm's law
• Parallel circuit
• Resistance
• Resonant cavities
• Series circuit
• Voltage
• Waveguides
Covariant formulation[show]
Scientists[show]
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• e
Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. The term complex impedance may be used interchangeably.
Quantitatively, the impedance of a two-terminal circuit element is the ratio of the complex representation of a sinusoidal voltage between its terminals to the complex representation of the current flowing through it.[1] In general, it depends upon the frequency of the sinusoidal voltage.
Impedance extends the concept of resistance to AC circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude. When a circuit is driven with direct current (DC), there is no distinction between impedance and resistance; the latter can be thought of as impedance with zero phase angle.
The notion of impedance is useful for performing AC analysis of electrical networks, because it allows relating sinusoidal voltages and currents by a simple linear law. In multiple port networks, the two-terminal definition of impedance is inadequate, but the complex voltages at the ports and the currents flowing through them are still linearly related by the impedance matrix.[2]
Impedance is a complex number, with the same units as resistance, for which the SI unit is the ohm (Ω). Its symbol is usually Z, and it may be represented by writing its magnitude and phase in the form |Z|∠θ. However, cartesian complex number representation is often more powerful for circuit analysis purposes.
The reciprocal of impedance is admittance, whose SI unit is the siemens, formerly called mho.
Instruments used to measure the electrical impedance are called impedance analyzers.
So if you have a impedance analyzer you can analyze it?
Electrical Impedance (Z), is the total opposition that a circuit presents to alternating current. Impedance is measured in ohms and may include resistance (R), inductive reactance (XL), and capacitive reactance (XC).
Simple impedance is calculated by simple 90 degree right angle math. The vertical line is the reactance, the horizontal line is the resistance and the angle line is the impedance. Using electronic symbols, R for Resistance, X for reactance, and Z for impedance we have R^2 +X^2=Z^2. The reactance is an alternating current resistance of capacitors and inductors. The value of the reactance varies with frequency, or cycles per period of time.
I hope this helps your understanding.
Yet another
Here is an understanding for beginners.
Suppose you have a coil of wire wrapped around a piece of iron.
Connect one end to the 0v of a battery and touch the other end to say the 12v positive terminal.
What will happen is this:
When you touch the 12v on the coil, a current will flow in the winding and this will produce magnetic flux. This flux is called EXPANDING FLUX and it will cut all the turns of the coil and produce a voltage in the turns that has an opposite potential to the applied voltage.
The voltage in each of the turns will add up and maybe result in a "back voltage" of 11.9v. This means the forward voltage is not 12v but only 0.1v.
This is the voltage that is really entering the coil and because the voltage is so small, only a very small current will flow.
This is why the initial current is very small.
The magnetic flux keeps expanding and opposing the incoming voltage but as it increases, it is not as effective at producing the same amount of back voltage and thus the forward voltage increases and the current increases. But this current does not produce the same amount of back voltage and so the current increases further.
This keeps happening and the flux keeps increasing and the current keeps increasing but the flux does not produce the same amount of back voltage as it did in the beginning. Eventually we get to a situation where the flux reaches a maximum but it is not EXPANDING FLUX (but STATIONARY FLUX) and it no longer produces ANY back voltage . So all the 12v from the battery is accepted by the coil and it produces the maximum magnetic flux but no back voltage is produced.
Also explained, because the above is not stated correctly due to the use of 12vdc and a coil
I'd like to explicitly stress one thing that his been implied in all the good descriptions above. Impedance is something defined for pure sinusoidal signals only. Of course everyone has stated it's for AC and mentions frequency, and even phase, which implies pure sinusoidal waves. But, it's important to stress the point because impedance makes no sense without pure sinusoidal waves.
“we” is correct to stress that one must understand resistance first because impedance is defined as an expansion of the idea of resistance. Ohm's law formula (V=IR) can be extended to sine waves (V=IZ) where the Z (impedance) is a complex number that captures the magnitude and phase relationship between the voltage sine wave and the current sine wave.
That's just the beginning of the explanation.
Another ! started with resistance
Resistance is a concept used for DC (direct currents) whereas impedance is the AC (alternating current) equivalent. Resistance is due to electrons in a conductor colliding with the ionic lattice of the conductor meaning that electrical energy is converted into heat.
What’s the difference?
Resistance is a concept used for DC (direct currents) whereas impedance is the AC (alternating current) equivalent.
Resistance is due to electrons in a conductor colliding with the ionic lattice of the conductor meaning that electrical energy is converted into heat. Different materials have different resistivities (a property defining how resistive a material of given dimensions will be).
However, when considering AC you must remember that it oscillates as a sine wave so the sign is always changing. This means that other effects need to be considered - namely inductance and capacitance.
Inductance is most obvious in coiled wire. When a current flows through a wire a circular magnetic field is created around it. If you coil the wire into a solenoid the fields around the wire sum up and you get a magnetic field similar to that of a bar magnet on the outside but you get a uniform magnetic field on the inside. With AC since the sign is always changing the direction of the field in the wires is always changing - so the magnetic field of the solenoid is also changing all the time. Now when field lines cut across a conductor an emf is generated in such a way to reduce the effects that created it (this is a combination of Lenz's and Faraday's laws which state mathematically that E=N*d(thi)/dt , where thi is the magnetic flux linkage). This means that when an AC current flows through a conductor a small back emf or back current is induced reducing the overall current.
Capacitance is a property best illustrated by two metal plates separated by an insulator (which we call a capacitor). When current flows electrons build up on the negative plate. An electric field propagates and repels electrons on the opposite plate making it positively charged. Due to the build up of electrons on the negative plate incoming electrons are also repelled so the total current eventually falls to zero in an exponential decay. The capacitance is defined as the charge stored/displaced across a capacitor divided by the potential difference across it and can also be calculated by the size of the plates and the primitively of the insulator.
So simply resistance and impedance have different fundamental origins even though the calculation for their value is the same:
R=V/I
Answered by: Martin Archer, Physics Student, Imperial College London, UK
Impedance is a more general term for resistance that also includes reactance.
In other words, resistance is the opposition to a steady electric current. Pure resistance does not change with frequency, and typically the only time only resistance is considered is with DC (direct current -- not changing) electricity.
Reactance, however, is a measure of the type of opposition to AC electricity due to capacitance or inductance. This opposition varies with frequency. For example, a capacitor only allows DC current to flow for a short while until it is charged; at that point, current will stop flowing and it will look like an open. However, if a very high frequency is put across that capacitor (a signal that has a voltage which is changing very quickly back and forth), the capacitor will look like a short circuit. The capacitor has a reactance which is inversely proportional to frequency. An inductor has a reactance which is directly proportional to frequency -- DC flows through easily while high-frequency AC is stopped.
Impedance is the total contribution of both -- resistance and reactance. This is important for AC analysis and design. At DC, reactive elements can be replaced with their steady-state model (capacitor->open,inductor->short) and resistance can be considered. (this isn't true for transient analysis)
It is important to mention that while energy goes into both, it is only 'burned off' through resistance. Power has to be given in terms of resistive power and reactive power. Resistive power actually burns off energy into heat while reactive power simply stores energy in E-fields and B-fields.
Often you'll hear about the 'impedance' of transmission lines, like the cables which run between components of your stereo system, and impedance of things like speakers. You'll also hear that it is important to match these or else you'll get reflection.
This is a much more complicated subject, which a few answers have commented on in recent questions about light and its speed.
However, what I want to mention is that when you hear about the impedance of a transmission line, like speaker cable or an antenna or coaxial cable or anything else, this does not represent energy which is "burned off" in the cable. This has to do with how energy is stored in the cable as it propagates down it. The cable does not (well, in reality it does, but assume the lossless case for simplicity) get hotter as a signal travels down it. It is not proper to think of a '75-ohm cable' as a 75-ohm 'resistor.' That 75-ohms is purely reactance (ideally, though there really is attenuation in real cables).
Note that impedance and reactance are both given in units of 'ohms' just like resistance. Capacitance is measured in Farads and inductance in Henries, and these relate to impedance, but they are not measures of impedance. As I said, the impedance of a capacitor is inversely proportional to its capacitance and the impedance of an inductor directly proportional to its inductance.
This may sound a little abstract. Impedance really is an abstraction of things that are far more complicated (things like time constants and rise times) that electrical engineers have to constantly consider. The idea of 'impedance' allows for many of these things to be wrapped up into one subject so that they are easier to communicate.
The short answer is -- impedance includes reactance, and reactance includes effects which vary with frequency due to inductance and capacitance.
Looking into impendence we ran across phasor ?????
The following equation was found:
V=IZ
this can then be described by using phasors as follows:
Here we take the reference to be the voltage V. This phasor would represent a series RLC circuit. As the current through the resistor is in phase with the voltage the phasor representing the impedance of the resistor is at 0 degrees to the voltage. The current through the capacitor leads the voltage by 90 degrees so the phasor representing the impedance of the capacitor is at 90 degrees to the voltage. Finally the current in an inductor lags the voltage by 90 degrees so the phasor representing the impedance of the inductor is at -90 degrees to the voltage.
The magnitude of the impedance is given:
and then the phase difference of the current to the reference voltage is:
Note: In the diagram the resulting impedance is shown to have a positive value for the phase difference (i.e. it leads the voltage), if the magnitude of the impedance of the inductor is more than the magnitude of the impedance of the capacitor then the angle will be negative (i.e. it lags the voltage).
So lets see
Impedance has to be calculated , assumed , know it’s a relevant, figured out in a formula , or just guess
,No you have to make a educated calculation
To be continued when I gather more information
Just know its important
Now almost all of this information is bits and pieces of work and definitions that I have gathered.
Although they are my thoughts I am not taking credit for this, I am just trying to help explain it as deep as I can
How I got started on this subject!
So here it goes
I stopped one of my workmates who was taking his CTS class and asked how he was doing
Not good, he was trying to understand impedance and asked what meter do I use to measure impedance.
I simply looked at the formula and said it’s not that easy
I asked if he understood inductance , he didn’t
As the conversation got longer it got harder
Finally I went to ohms law,
And started from scratch
From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Part of a series of articles about
Electromagnetism
• Electricity
• Magnetism
Electrostatics[show]
Magnetostatics[show]
Electrodynamics[show]
Electrical network[hide]
• Alternating current
• Capacitance
• Direct current
• Electric current
• Electric potential
• Electromotive force
• Impedance
• Inductance
• Ohm's law
• Parallel circuit
• Resistance
• Resonant cavities
• Series circuit
• Voltage
• Waveguides
Covariant formulation[show]
Scientists[show]
• v
• t
• e
Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. The term complex impedance may be used interchangeably.
Quantitatively, the impedance of a two-terminal circuit element is the ratio of the complex representation of a sinusoidal voltage between its terminals to the complex representation of the current flowing through it.[1] In general, it depends upon the frequency of the sinusoidal voltage.
Impedance extends the concept of resistance to AC circuits, and possesses both magnitude and phase, unlike resistance, which has only magnitude. When a circuit is driven with direct current (DC), there is no distinction between impedance and resistance; the latter can be thought of as impedance with zero phase angle.
The notion of impedance is useful for performing AC analysis of electrical networks, because it allows relating sinusoidal voltages and currents by a simple linear law. In multiple port networks, the two-terminal definition of impedance is inadequate, but the complex voltages at the ports and the currents flowing through them are still linearly related by the impedance matrix.[2]
Impedance is a complex number, with the same units as resistance, for which the SI unit is the ohm (Ω). Its symbol is usually Z, and it may be represented by writing its magnitude and phase in the form |Z|∠θ. However, cartesian complex number representation is often more powerful for circuit analysis purposes.
The reciprocal of impedance is admittance, whose SI unit is the siemens, formerly called mho.
Instruments used to measure the electrical impedance are called impedance analyzers.
So if you have a impedance analyzer you can analyze it?
Electrical Impedance (Z), is the total opposition that a circuit presents to alternating current. Impedance is measured in ohms and may include resistance (R), inductive reactance (XL), and capacitive reactance (XC).
Simple impedance is calculated by simple 90 degree right angle math. The vertical line is the reactance, the horizontal line is the resistance and the angle line is the impedance. Using electronic symbols, R for Resistance, X for reactance, and Z for impedance we have R^2 +X^2=Z^2. The reactance is an alternating current resistance of capacitors and inductors. The value of the reactance varies with frequency, or cycles per period of time.
I hope this helps your understanding.
Yet another
Here is an understanding for beginners.
Suppose you have a coil of wire wrapped around a piece of iron.
Connect one end to the 0v of a battery and touch the other end to say the 12v positive terminal.
What will happen is this:
When you touch the 12v on the coil, a current will flow in the winding and this will produce magnetic flux. This flux is called EXPANDING FLUX and it will cut all the turns of the coil and produce a voltage in the turns that has an opposite potential to the applied voltage.
The voltage in each of the turns will add up and maybe result in a "back voltage" of 11.9v. This means the forward voltage is not 12v but only 0.1v.
This is the voltage that is really entering the coil and because the voltage is so small, only a very small current will flow.
This is why the initial current is very small.
The magnetic flux keeps expanding and opposing the incoming voltage but as it increases, it is not as effective at producing the same amount of back voltage and thus the forward voltage increases and the current increases. But this current does not produce the same amount of back voltage and so the current increases further.
This keeps happening and the flux keeps increasing and the current keeps increasing but the flux does not produce the same amount of back voltage as it did in the beginning. Eventually we get to a situation where the flux reaches a maximum but it is not EXPANDING FLUX (but STATIONARY FLUX) and it no longer produces ANY back voltage . So all the 12v from the battery is accepted by the coil and it produces the maximum magnetic flux but no back voltage is produced.
Also explained, because the above is not stated correctly due to the use of 12vdc and a coil
I'd like to explicitly stress one thing that his been implied in all the good descriptions above. Impedance is something defined for pure sinusoidal signals only. Of course everyone has stated it's for AC and mentions frequency, and even phase, which implies pure sinusoidal waves. But, it's important to stress the point because impedance makes no sense without pure sinusoidal waves.
“we” is correct to stress that one must understand resistance first because impedance is defined as an expansion of the idea of resistance. Ohm's law formula (V=IR) can be extended to sine waves (V=IZ) where the Z (impedance) is a complex number that captures the magnitude and phase relationship between the voltage sine wave and the current sine wave.
That's just the beginning of the explanation.
Another ! started with resistance
Resistance is a concept used for DC (direct currents) whereas impedance is the AC (alternating current) equivalent. Resistance is due to electrons in a conductor colliding with the ionic lattice of the conductor meaning that electrical energy is converted into heat.
What’s the difference?
Resistance is a concept used for DC (direct currents) whereas impedance is the AC (alternating current) equivalent.
Resistance is due to electrons in a conductor colliding with the ionic lattice of the conductor meaning that electrical energy is converted into heat. Different materials have different resistivities (a property defining how resistive a material of given dimensions will be).
However, when considering AC you must remember that it oscillates as a sine wave so the sign is always changing. This means that other effects need to be considered - namely inductance and capacitance.
Inductance is most obvious in coiled wire. When a current flows through a wire a circular magnetic field is created around it. If you coil the wire into a solenoid the fields around the wire sum up and you get a magnetic field similar to that of a bar magnet on the outside but you get a uniform magnetic field on the inside. With AC since the sign is always changing the direction of the field in the wires is always changing - so the magnetic field of the solenoid is also changing all the time. Now when field lines cut across a conductor an emf is generated in such a way to reduce the effects that created it (this is a combination of Lenz's and Faraday's laws which state mathematically that E=N*d(thi)/dt , where thi is the magnetic flux linkage). This means that when an AC current flows through a conductor a small back emf or back current is induced reducing the overall current.
Capacitance is a property best illustrated by two metal plates separated by an insulator (which we call a capacitor). When current flows electrons build up on the negative plate. An electric field propagates and repels electrons on the opposite plate making it positively charged. Due to the build up of electrons on the negative plate incoming electrons are also repelled so the total current eventually falls to zero in an exponential decay. The capacitance is defined as the charge stored/displaced across a capacitor divided by the potential difference across it and can also be calculated by the size of the plates and the primitively of the insulator.
So simply resistance and impedance have different fundamental origins even though the calculation for their value is the same:
R=V/I
Answered by: Martin Archer, Physics Student, Imperial College London, UK
Impedance is a more general term for resistance that also includes reactance.
In other words, resistance is the opposition to a steady electric current. Pure resistance does not change with frequency, and typically the only time only resistance is considered is with DC (direct current -- not changing) electricity.
Reactance, however, is a measure of the type of opposition to AC electricity due to capacitance or inductance. This opposition varies with frequency. For example, a capacitor only allows DC current to flow for a short while until it is charged; at that point, current will stop flowing and it will look like an open. However, if a very high frequency is put across that capacitor (a signal that has a voltage which is changing very quickly back and forth), the capacitor will look like a short circuit. The capacitor has a reactance which is inversely proportional to frequency. An inductor has a reactance which is directly proportional to frequency -- DC flows through easily while high-frequency AC is stopped.
Impedance is the total contribution of both -- resistance and reactance. This is important for AC analysis and design. At DC, reactive elements can be replaced with their steady-state model (capacitor->open,inductor->short) and resistance can be considered. (this isn't true for transient analysis)
It is important to mention that while energy goes into both, it is only 'burned off' through resistance. Power has to be given in terms of resistive power and reactive power. Resistive power actually burns off energy into heat while reactive power simply stores energy in E-fields and B-fields.
Often you'll hear about the 'impedance' of transmission lines, like the cables which run between components of your stereo system, and impedance of things like speakers. You'll also hear that it is important to match these or else you'll get reflection.
This is a much more complicated subject, which a few answers have commented on in recent questions about light and its speed.
However, what I want to mention is that when you hear about the impedance of a transmission line, like speaker cable or an antenna or coaxial cable or anything else, this does not represent energy which is "burned off" in the cable. This has to do with how energy is stored in the cable as it propagates down it. The cable does not (well, in reality it does, but assume the lossless case for simplicity) get hotter as a signal travels down it. It is not proper to think of a '75-ohm cable' as a 75-ohm 'resistor.' That 75-ohms is purely reactance (ideally, though there really is attenuation in real cables).
Note that impedance and reactance are both given in units of 'ohms' just like resistance. Capacitance is measured in Farads and inductance in Henries, and these relate to impedance, but they are not measures of impedance. As I said, the impedance of a capacitor is inversely proportional to its capacitance and the impedance of an inductor directly proportional to its inductance.
This may sound a little abstract. Impedance really is an abstraction of things that are far more complicated (things like time constants and rise times) that electrical engineers have to constantly consider. The idea of 'impedance' allows for many of these things to be wrapped up into one subject so that they are easier to communicate.
The short answer is -- impedance includes reactance, and reactance includes effects which vary with frequency due to inductance and capacitance.
Looking into impendence we ran across phasor ?????
The following equation was found:
V=IZ
this can then be described by using phasors as follows:
Here we take the reference to be the voltage V. This phasor would represent a series RLC circuit. As the current through the resistor is in phase with the voltage the phasor representing the impedance of the resistor is at 0 degrees to the voltage. The current through the capacitor leads the voltage by 90 degrees so the phasor representing the impedance of the capacitor is at 90 degrees to the voltage. Finally the current in an inductor lags the voltage by 90 degrees so the phasor representing the impedance of the inductor is at -90 degrees to the voltage.
The magnitude of the impedance is given:
and then the phase difference of the current to the reference voltage is:
Note: In the diagram the resulting impedance is shown to have a positive value for the phase difference (i.e. it leads the voltage), if the magnitude of the impedance of the inductor is more than the magnitude of the impedance of the capacitor then the angle will be negative (i.e. it lags the voltage).
So lets see
Impedance has to be calculated , assumed , know it’s a relevant, figured out in a formula , or just guess
,No you have to make a educated calculation
To be continued when I gather more information
Just know its important
Phasors simply phase me without a diagram!
Good compilation of information, but could benefit from subheadings.
Looking forward to the next instalment. 😎
Galu you should just jump ahead to "Defining BD a computation" i think that's the next installment (and i might be wrong but i think it's supposed to be DB not BD)
Wow! I didn't know there was so much to know about dBs!
P.S. You say installment and I say instalment - aren't words great? - and the more the merrier! 🙂
it'sastalemint? and yes i've learnt or is that sumposed to be learned a lot too 'bout BD's and such...time for contemplation and more scotch!!!!!!!
I was going to pull this whole thing down because it didn't paste as I hoped it would.
Should I just discard and do it over?
Should I just discard and do it over?
Can't fault you for trying, but explaining impedance to the layperson is no easy task.
Perhaps you could break your treatise up into shorter bite size chunks which are easier to digest. For example:
- DC resistance and ohm's law
- Opposition to AC and reactance
- LRC circuits and phasor diagrams
P.S. Luv u 2! 😎
I have all this time on my hands due to the most amazing retirement job.
And yes pick a subject and break it down into bits or is it bite's
So basically in this case i should have stuck to a 16 bit word instead of jumping to 128.
Thanks and no i wont forget my stop bit's
Time to think
And yes pick a subject and break it down into bits or is it bite's
So basically in this case i should have stuck to a 16 bit word instead of jumping to 128.
Thanks and no i wont forget my stop bit's
Time to think
Biciletta
I looked this up and the simplest explanation is not simple at all
Mechanical impedance is a measure of how much a structure resists motion when subjected to a harmonic force. It relates forces with velocities acting on a mechanical system. The mechanical impedance of a point on a structure is the ratio of the force applied at a point to the resulting velocity at that point.[1][2]
Mechanical impedance is the inverse of mechanical admittance or mobility. The mechanical impedance is a function of the frequency
the applied force and can vary greatly over frequency.
At resonance frequencies, the mechanical impedance will be lower, meaning less force is needed to cause a structure to move at a given velocity.
A simple example of this is pushing a child on a swing.
For the greatest swing amplitude, the frequency of the pushes must be near the resonant frequency of the system.
Mechanical impedance is the ratio of a potential (e.g. force) to a flow (e.g. velocity) where the arguments of the real (or imaginary) parts of both increase linearly with time. Examples of potentials are: force, sound pressure, voltage, temperature. Examples of flows are: velocity, volume velocity, current, heat flow. Impedance is the reciprocal of mobility. If the potential and flow quantities are measured at the same point then impedance is referred as driving point impedance; otherwise, transfer impedance.
Resistance - the real part of an impedance.
Reactance - the imaginary part of an impedance.
I hope that partially helps , What specifically are you referring to?
Cheers
I looked this up and the simplest explanation is not simple at all
Mechanical impedance is a measure of how much a structure resists motion when subjected to a harmonic force. It relates forces with velocities acting on a mechanical system. The mechanical impedance of a point on a structure is the ratio of the force applied at a point to the resulting velocity at that point.[1][2]
Mechanical impedance is the inverse of mechanical admittance or mobility. The mechanical impedance is a function of the frequency
the applied force and can vary greatly over frequency.
At resonance frequencies, the mechanical impedance will be lower, meaning less force is needed to cause a structure to move at a given velocity.
A simple example of this is pushing a child on a swing.
For the greatest swing amplitude, the frequency of the pushes must be near the resonant frequency of the system.
Mechanical impedance is the ratio of a potential (e.g. force) to a flow (e.g. velocity) where the arguments of the real (or imaginary) parts of both increase linearly with time. Examples of potentials are: force, sound pressure, voltage, temperature. Examples of flows are: velocity, volume velocity, current, heat flow. Impedance is the reciprocal of mobility. If the potential and flow quantities are measured at the same point then impedance is referred as driving point impedance; otherwise, transfer impedance.
Resistance - the real part of an impedance.
Reactance - the imaginary part of an impedance.
I hope that partially helps , What specifically are you referring to?
Cheers
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