225kW Variable Speed Motor 13

[Anode]

Hi All,
I was looking into some form of soft starter for a 225kW induction motor on a ship, when the thought of variable
speed drive came to mind. As the motor is driving a pump, the thought of being able to regulate the starting current as well as having speed control would be a bonus.
My question is: are induction motors suitable for use with a vsd?
Thank you in advance.

 

[jraef]

Anode,
Slings and arrows aside, there was good advice from both parties buried in the above posts. I for one do not recommend immediately replacing standard induction motors when VFDs are added. You already own that motor, why not see if it works out OK? As Jomega indicated, the vast majority do, as long as some prudent precautions are taken, i.e. the filtering that he mentioned. IMHO, do not even consider a VFD without considering filtering. And speaking of that, jbartos made a good point earlier about nearby electrical equipment getting interference. Think of a VFD as a good sized FM radio transmitter. On shipboard that can be problematic. Take all of your application information and concerns to a filter supplier and do not skimp. Do NOT trust the VFD manufacturer to do this for you. For the most part they have a different agenda, namely that you buy the VFD. If possible, hire an integrator with experience in this field. You will be successful.

Quando Omni Flunkus Moritati

 

[GusD]

Hello Anode

Anode,induction motors and VFDs are employed on a multitude of applications world over.If you have a need for a VFD.somebody will come up with one to suit your application.
I was very impressed by the capabilities of Magnectic Couplings manufactured by MAGNA DRIVES.These devices provide great spped control,no physical connection from Driver to Driven load and can be controlled by a simple remote 4 /20 mA from a PLC.It can use a standard Induction motor and no worries about Harmonics,filtering and all the other things associated with VFDs.This Technology is fairly new ,but I believe we all will be hearing about it more in the future.They can go as high as 1500 Hp and if I was looking for an adjustable speed system to drive a pump,I would definitely look into it.

Good Luck.

GusD

 

[jOmega]

To correct a mis-conception from JB's post on the TCI HarmonicGuard filter; it is designed for mitigation of the 5th harmonic on the line (mains) side of the VFD in attempt to attain compliance with IEEE 519-1992. It is not designed for use at the output of the drive or for dv/dt (du/dt) reduction.

The KLC filter from TCI (TransCoil Inc) is the product intended to reduce dv/dt (du/dt) at the motor. The filter is applied at the output of the VFD and the motor is connected to the filter.

See: KLC Drive Output Filters

http://www.transcoil.com/#klc

They also make a sinewave filter that filters the PWM voltage pulses into a sinewave voltage for application to the motor. In addition to dv/dt(du/dt) reduction, the filter also attenuates the audible noise produced in the motor by the VFD switching frequency and its harmonics.
Note: While this filter will virtually eliminate the audible noise in the motor, the magnetics in the filter will sing.... If that is a concern, contact TCI for an engineered solution that applies some dampening techniques to the inductors.

See: MotorGuard - KMG Sine Wave Filter

http://www.transcoil.com/#kmg

 

[afterhrs]

Anode,
After reading your other threads, you either work for a shipbuilder or consult with one. I guess this application is for large ship, +400 feet long. I would definitely check out the U.S.Coast Guard electrical regulations and the U.S.Navy's "Navsea" department(the are responible for Navy engineering and regulations.
You also might want look for a component that meets "military specification" (mil-spec for short).
It has been 10 years since i have been on a boat, but I remember "mil-spec" equipment being pretty robust.

Regards,
Afterhrs

 

[Anode]

Afterhrs,

You are right on all counts. I am currently working in a shipyard as a consultant for a tanker (750 feet) conversion.
I used to be in the military myself and appreciate the "mil-spec" construction criteria. Thanks for the tips, and to everyone else here who has contributed.

Cheers
Anode

 

[jbartos]

Suggestion to jOmega (Electrical) Aug 10, 2003 marked ///\\To correct a mis-conception from JB's post on the TCI HarmonicGuard filter; it is designed for mitigation of the 5th harmonic on the line (mains) side of the VFD in attempt to attain compliance with IEEE 519-1992.

///Yes, this is true. However, it may be used on the VFD output side to mitigate harmonics as I posted in my previous posting that is criticized by jOmega.\\
It is not designed for use at the output of the drive or for dv/dt (du/dt) reduction.

///Yes, agree. I never stated anywhere that it is used for that purpose. In fact, I indicated in my posting:
"Besides the VFD output dv/dt filters, as posted by JOmega, there are also harmonic filters for the VFD output, e.g. HarmonicGuard available at:

http://www.transcoil.com

http://www.transcoil.com/#khg"\\

The KLC filter from TCI (TransCoil Inc) is the product intended to reduce dv/dt (du/dt) at the motor. The filter is applied at the output of the VFD and the motor is connected to the filter.

///Never disputed, never denied. I am very familiar with these filters and their purpose in VFD context.\\
See: KLC Drive Output Filters

http://www.transcoil.com/#klc

They also make a sinewave filter that filters the PWM voltage pulses into a sinewave voltage for application to the motor. In addition to dv/dt(du/dt) reduction,

///This feature is not associated with the KMG filter. It is associated with "dV/dTGuard KLC Filter Motor-Protecting Output Filter"

http://www.transcoil.com/#klc

""The dV/dTGuard product family has been designed as an engineered solution for motor failures due to the reflected wave phenomenon.""\\
the filter also attenuates the audible noise produced in the motor by the VFD switching frequency and its harmonics.

///To correct jOmega misconception, the following is stated at

http://www.transcoil.com/#kmg

""The KMG filter is designed to attenuate the carrier components present in the output waveform of typical PWM output power supplies.""
See: MotorGuard - KMG Sine Wave Filter

http://www.transcoil.com/#kmg

\\
Note: While this filter will virtually eliminate the audible noise in the motor, the magnetics in the filter will sing.... If that is a concern, contact TCI for an engineered solution that applies some dampening techniques to the inductors.

See: MotorGuard - KMG Sine Wave Filter

http://www.transcoil.com/#kmg

///To summarize the corrections (and misconceptions posted by jOmega):
1. dV/dTGuard KLC Filter Motor-Protecting Output Filter"

http://www.transcoil.com/#klc

is to mitigate dV/dt effects

2. MotorGuard - KMG Sine Wave Filter

http://www.transcoil.com/#kmg

is to mitigate carrier frequency components and associated harmonics.

3. HarmonicGuard available at:

http://www.transcoil.com/#khg

is to mitigate harmonics on the VFD input. However, it is designed to mitigate harmonics in general. Harmonics due to wave distortion caused by the VFD switching topology are still present on the VFD output. There are oscilloscope traces available of some manufacturers VFD outputs. Also, the harmonic content is possible to measure on the VFD output by the harmonic analyzer. It appears that jOmega is not aware of this.\\\

 

[jOmega]

Sorry JB, but the knowledgable folks at TCI state that the HarmonicGuard Filter is NOT DESIGNED to be used on the output of the VFD.....period. You'll fry it! Components not selected/rated for frequency components present in the output of the VFD.

If you'd like, I'll be happy to put you in touch with their VP Engineering who can explain it to you . Perhaps then you'll believe me when I tell you that it cannot be used at the output of VFDs....

And JB.... here is what you said.... and I quote (in blue):

"jbartos (Electrical) Jun 25, 2003
Suggestion: Besides the VFD output dv/dt filters, as posted by JOmega, there are also harmonic filters for the VFD output, e.g. HarmonicGuard available at:

http://www.transcoil.com"

JB you also made the same error in your Aug 16. post above, in several places..... and I quote (in blue) ....

"jbartos (Electrical) Aug 16, 2003
Suggestion to jOmega (Electrical) Aug 10, 2003 marked ///\\\
{jO said}To correct a mis-conception from JB's post on the TCI HarmonicGuard filter; it is designed for mitigation of the 5th harmonic on the line (mains) side of the VFD in attempt to attain compliance with IEEE 519-1992.{end jO's comment}

{JB said}///Yes, this is true. However, it may be used on the VFD output side to mitigate harmonics as I posted in my previous posting that is criticized by jOmega.\\\ {end JB comment}

{jO comment} It is not designed for use at the output of the drive or for dv/dt (du/dt) reduction."{end jO comment}

{JB comment} "///Yes, agree. I never stated anywhere that it is used for that purpose. In fact, I indicated in my posting:
"'Besides the VFD output dv/dt filters, as posted by JOmega, there are also harmonic filters for the VFD output, e.g. HarmonicGuard available at:

http://www.transcoil.com"'

Here again, JB, you stated that the HarmonicGuard filter could be used at the VFD OUTPUT

Which as I said previously and above, is just not true. The HarmonicGuard CANNOT be used at the output of any VFD. It is designed SOLELY for use on the 50/60 HZ mains.

The issue JB, is NOT whether or not the filter is servicable for dv(du)/dt reduction or whether it is for harmonic reduction; the issue is that it is NOT designed to be used on the output of VFDs. The HarmonicGuard Filter, as the engineers at TCI will tell you, is designed ONLY for use on 50/60 Hz Mains; and must never be connected the output of a VFD else it will cause damage to the HarmonicGuard filter.

JB, I hope you understand that now. If not contact me at jomega@email.com with a phone number at which you can be reached and I'll be happy to have a TCI engineer contact you to reiterate the reasons why the HarmonicGuard filter cannot be connected to the output of a VFD.

I'm sure you don't want to see someone misapply the HarmonicGuard filter and damage it and/the VFD it is mistakenly connected to, now do you?

Ok ? Are we clear on the use and non-use of the HarmonicGuard filter ?

NEXT.... you said (in your Aug. 16 post above.. and I quote in blue...


{jO comment} See: KLC Drive Output Filters

http://www.transcoil.com/#klc

They also make a sinewave filter that filters the PWM voltage pulses into a sinewave voltage for application to the motor. In addition to dv/dt(du/dt) reduction, {end jO comment}

{JB comment}///This feature is not associated with the KMG filter. It is associated with "dV/dTGuard KLC Filter Motor-Protecting Output Filter"{end JB comment}

Well, JB, you leave me no choice but to take issue with you again.... In a meeting at TCI about 4 weeks ago, their chief engineer stated that the KMG filter does indeed attenuate dv/dt and does so very nicely. You see, the KMG is a low pass filter design, and its output is virtualy sinusoidal. Ergo, it does not introduce step voltages (with steep wave fronts) into the wiring between the drive and motor that exhibits transmission line or tank circuit (your choice)characteristics and produces standing waves therein. As I said, the output of the KMG is a pretty good sinewave at fundamental frequency.... and so...effects DV/DT reduction at the motor...

Ok ? If not we can include this in the phone call to you from TCI....

And finally, JB, your last statements.... quoted below in blue...


3. HarmonicGuard available at:

http://www.transcoil.com/#khg

is to mitigate harmonics on the VFD input. However, it is designed to mitigate harmonics in general. Harmonics due to wave distortion caused by the VFD switching topology are still present on the VFD output. There are oscilloscope traces available of some manufacturers VFD outputs. Also, the harmonic content is possible to measure on the VFD output by the harmonic analyzer. It appears that jOmega is not aware of this.\\\


JB, the HarmonicGuard is designed as a somewhat broadly tuned 5th harmonic trap. Broadly because there's some spillover to catch some of the 7th... as well as covering the 5th on 50 Hz mains ...

It is not, as you stated, a harmonic reduction filter; it is a trap filter for limited, specific frequencies....i.e the 5th harmonic of the mains fundamental frequency.

It won't do squat for you on the output of the VFD which has much higher frequency content, other than fry....


p.s.... JB, the KLC filter doesn't do squat for removal of audible noise from the motor.... That filter rolls of somewhere in the 20-30 kHZ range....filter is designed to produce some softening of the wavefronts of the output voltage pulses from the VFD.

We can also include this in the discussion with TCI .... I'll let them set you straight on this as well.

 

[ozmosis]

A bit late in repsonding but an interesting discussion all the same. As product manager for a large drives company, I thought I'd offer a few points:
1) First the motor issue. There's been no mention of supply voltage. If your supply voltage is >500V then be very careful fitting a VSD (or ASD if you prefer!). If you go for a PWM (Pulse Width Modulating) drive (the most common) then the peak to peak voltage spikes will very quickly cause problems on motors rated at >500VAC. Check the manufacturer of the motor!
2)Onto the VSD. Be very careful when applying VSD's due to the increased leakage current you will get from all makes unless the design of the drive has been specially looked into. Generally this means quite a level of board isolation to ensure any internal filtering has the minimum leakage. We try and achieve something in the region of 2mA max.
3) If you have to fit an RFI(Radio Frequency Interference) Filter as somebody suggested in the threads, make sure it has been specifically designed so that the Y (wye) capacitor has been disabled (cut). This reduces the high leakage current from a filter that is basically made up of capacitors. The supplier of the drive will know what you mean (there's a test for them!)
Why is leakage current a problem? well, if you know about ships you will know the answer but for those in the thread who don't, it rots the hull. Most(all I think)ships have a sacrificial cathode that will basically absord any leakage current and this will rot away rather than the hull, but it is very expensive and ship owners would rather not have it go too quickly as their maintenance costs rise rapidly.
I'm sure there are other reasons but this seems to be the main one from a drives developers point of view with ships in mind.
4) There are various standards and approvals ship manufacturers will role out with regards putting electrical devices on their vessel. One is DNV (Det Norske Veritas). This demands the drive to be stamped up with DNV and to be issued with a certificate to say you have paid the extortionate fees demanded by DNV. The other is Lloyds approval. This is another tortuous route drive manufacturers have to go down. Necessary but very costly. Insurance companies rule the waves!
There are very few companies who have dared go down this route. Siemens is one (ok, you found me out) but Danfoss and Vacon are others. I would imagine ABB do but I am only aware of their large MW propulsion drives that are part of the ship anyway.
5) There's been a lot of mention of harmonic filters and the like. I would check with the manufacturer to see if they have the absolute minimum leakage current as the majority of passive harmonic filters include a fair proportion of capacitors.

I trust this doesn't scare you off. A VSD should always be supplied to give you control. A by-product of good control is energy savings. People like talking about energy savings because the accountants in companies can see return on their investment. The ROI can be anything from 6 months +, usually the '+' increases due to badly applied drives! Always go with a reputable drive company, they should always provide the balance!

 

[Skogsgurra]

Dear sed2developer,

I have been looking for data on corrosion caused by VFDs for some time now. You seem to have some references. Could you please share them with us in this thread? My interest is not only in shipping, but in pumps, seals etcetera.

 

[jbartos]

Comment on jOmega (Electrical) Aug 17, 2003 marked ///\\Sorry JB, but the knowledgable folks at TCI state that the HarmonicGuard Filter is NOT DESIGNED to be used on the output of the VFD.....period. You'll fry it! Components not selected/rated for frequency components present in the output of the VFD.
///Surprise, surprise. The output of the VFD by applying the applicable TCI filter is supposed to be almost ideal sinusoidal wave. Then, it is said that the ideal sinusoidal wave would fry the HarmonicGuard Filter. This does not make any sense. What good is the HarmonicGuard if it cannot withstand the almost pure sinusoidal wave?\\If you'd like, I'll be happy to put you in touch with their VP Engineering who can explain it to you . Perhaps then you'll believe me when I tell you that it cannot be used at the output of VFDs....
///I would not engineer and design the HarmonicGuard in front of:
"dV/dTGuard KLC Filter Motor-Protecting Output Filter"
and
"MotorGuard - KMG Sine Wave Filter"
since these are designed to mitigate higher frequency contaminations.\\
And JB.... here is what you said.... and I quote (in blue):
"jbartos (Electrical) Jun 25, 2003
Suggestion: Besides the VFD output dv/dt filters, as posted by JOmega, there are also harmonic filters for the VFD output, e.g. HarmonicGuard available at:

http://www.transcoil.com";

JB you also made the same error in your Aug 16. post above, in several places..... and I quote (in blue) ....
///Just make sure that you do not make errors. See my first comment above.\\"jbartos (Electrical) Aug 16, 2003
Suggestion to jOmega (Electrical) Aug 10, 2003 marked ///\\{jO said}To correct a mis-conception from JB's post on the TCI HarmonicGuard filter; it is designed for mitigation of the 5th harmonic on the line (mains) side of the VFD in attempt to attain compliance with IEEE 519-1992.{end jO's comment}

{JB said}///Yes, this is true. However, it may be used on the VFD output side to mitigate harmonics as I posted in my previous posting that is criticized by jOmega.\\\ {end JB comment}

{jO comment} It is not designed for use at the output of the drive or for dv/dt (du/dt) reduction."{end jO comment}
///I never stated that the HarmonicGuard is to be solely applied on the VFD output. This is where things are becoming twisted by J.Omega.\\{JB comment} "///Yes, agree. I never stated anywhere that it is used for that purpose. In fact, I indicated in my posting:
"'Besides the VFD output dv/dt filters, as posted by JOmega, there are also harmonic filters for the VFD output, e.g. HarmonicGuard available at:

http://www.transcoil.com";'

Here again, JB, you stated that the HarmonicGuard filter could be used at the VFD OUTPUT
///Yes, I justified my reasoning behind it in my first reply above.\\Which as I said previously and above, is just not true. The HarmonicGuard CANNOT be used at the output of any VFD. It is designed SOLELY for use on the 50/60 HZ mains.
///This does not sound credible that the HarmonicGuard would not withstand almost sinusoidal wave accomplished by other filters on the VFD output. In fact the harmonic currents are flowing from the motor into the HarmonicGard filter, the same way as on the VFD input side. Motor produces significant 5th, 7th and 9th harmonics. Where are these mitigated on the VFD output?\\The issue JB, is NOT whether or not the filter is servicable for dv(du)/dt reduction or whether it is for harmonic reduction; the issue is that it is NOT designed to be used on the output of VFDs. The HarmonicGuard Filter, as the engineers at TCI will tell you, is designed ONLY for use on 50/60 Hz Mains; and must never be connected the output of a VFD else it will cause damage to the HarmonicGuard filter.
///Please, see my comment above.\\JB, I hope you understand that now.
///I hope you understand now.\\ If not contact me at jomega@email.com with a phone number at which you can be reached and I'll be happy to have a TCI engineer contact you to reiterate the reasons why the HarmonicGuard filter cannot be connected to the output of a VFD.
///Perhaps, under some conditions.\\\

I'm sure you don't want to see someone misapply the HarmonicGuard filter and damage it and/the VFD it is mistakenly connected to, now do you?
///I am more concerned about the 5th, 7th, 9th, etc. harmonics, that are not being treated on the VFD output or on the motor input. I do not see them addressed by J.Omega, TCI, etc. However, I did have them addressed during various VFD presentations by the VFD manufacturers, e.g. Magnetek in the past.\\Ok ? Are we clear on the use and non-use of the HarmonicGuard filter ?
///Far appart as at the beginning.\\NEXT.... you said (in your Aug. 16 post above.. and I quote in blue...

{jO comment} See: KLC Drive Output Filters

http://www.transcoil.com/#klc

They also make a sinewave filter that filters the PWM voltage pulses into a sinewave voltage for application to the motor. In addition to dv/dt(du/dt) reduction, {end jO comment}

{JB comment}///This feature is not associated with the KMG filter. It is associated with "dV/dTGuard KLC Filter Motor-Protecting Output Filter"{end JB comment}

Well, JB, you leave me no choice but to take issue with you again.... In a meeting at TCI about 4 weeks ago, their chief engineer stated that the KMG filter does indeed attenuate dv/dt and does so very nicely.
///This seems to be contradicting what is posted on TCI website and what I posted above, namely:
1. dV/dTGuard KLC Filter Motor-Protecting Output Filter"

http://www.transcoil.com/#klc

is to mitigate dV/dt effects
\\ You see, the KMG is a low pass filter design, and its output is virtualy sinusoidal. Ergo, it does not introduce step voltages (with steep wave fronts) into the wiring between the drive and motor that exhibits transmission line or tank circuit (your choice)characteristics and produces standing waves therein. As I said, the output of the KMG is a pretty good sinewave at fundamental frequency.... and so...effects DV/DT reduction at the motor...
///How comes that the HarmonicGuard would "fry" in such perfect conditions on the VFD output.\\Ok ? If not we can include this in the phone call to you from TCI....
///Thank you for your services. I follow engineering and design. I would like to witness that "frying" of HarmonicGuard filter" on perfectly sinusoidal input.\\And finally, JB, your last statements.... quoted below in blue...
3. HarmonicGuard available at:

http://www.transcoil.com/#khg

is to mitigate harmonics on the VFD input. However, it is designed to mitigate harmonics in general. Harmonics due to wave distortion caused by the VFD switching topology are still present on the VFD output. There are oscilloscope traces available of some manufacturers VFD outputs. Also, the harmonic content is possible to measure on the VFD output by the harmonic analyzer. It appears that jOmega is not aware of this.\\
JB, the HarmonicGuard is designed as a somewhat broadly tuned 5th harmonic trap.
///Are you aware that induction motor creates 5th harmonic on its input which flows toward the power supply?\\ Broadly because there's some spillover to catch some of the 7th... as well as covering the 5th on 50 Hz mains ...
///Are you aware that induction motor creates 7th harmonic on its input which flows toward the power supply?\\It is not, as you stated, a harmonic reduction filter; it is a trap filter for limited, specific frequencies....i.e the 5th harmonic of the mains fundamental frequency.
///Do you happen to know in which direction current harmonics flow? The HarmonicGuard filter mitigates harmonics flowing from the AC-DC converter (rectifier) to the input power supply. This is why there is IEEE Std 519.\\It won't do squat for you on the output of the VFD which has much higher frequency content, other than fry....
///Certainly, entitled to your own opinion and expertise.\\
p.s.... JB, the KLC filter doesn't do squat for removal of audible noise from the motor.... That filter rolls of somewhere in the 20-30 kHZ range....filter is designed to produce some softening of the wavefronts of the output voltage pulses from the VFD.
///I posted the following information from the manufacturer web site in my previous posting, namely:
/This feature is not associated with the KMG filter. It is associated with "dV/dTGuard KLC Filter Motor-Protecting Output Filter"

http://www.transcoil.com/#klc

""The dV/dTGuard product family has been designed as an engineered solution for motor failures due to the reflected wave phenomenon.""\\We can also include this in the discussion with TCI .... I'll let them set you straight on this as well.
///I do not have to. I feel reasonably comfortable with what the TCI offers and advertises.\\

 

[Skogsgurra]

jbartos,

I think that your endless postings about anything and everything are getting very tiring. And the way you try to "prove" that you are always right are even more so. In this discussion (and many other) you seem to be unable to understand where your limits are.

I am sure that you have some expertise in some technical field (power transmission perhaps?) but what you are writing in this is pure non-sense.

Someone has to put an end to this.

 

[design2003]

Yes! Inverter duty induction motor should be selected.

 

[peebee]

Here's my two cents:

I generally agree with the above posts. You can probably do a straight retrofit of your starter with a VFD. Some notes on that:

1. You should limit low speed -- someone else said to 70% of rated speed, I'd say maybe as low as 50%. Check with your motor vendor. No doubt about it, you cannot run your pump at full load and 10% speed all day. The only gray area is just how low you can go and be OK.

2. Switching speed (kHz) of the VFD has a big impact on efficiency, harmonics, ground currents (and hull rotting), motor life, etc. Have a good long talk with both your motor and VFD vendor on this -- maybe. Then again, there's a reasonable chance that you could neglect this and be OK if you're the gambling sort.

3. Ground currents can pit or flute your motor bearings and downstream pump bearings. You might want to investigate the installation of a shaft grounding device (essentially a grounded brush) to prevent that. Then again, you can maybe forget about that and be OK.

I'm reasonably confident that if you pick a good number for the low-end motor speed, and if your distribution sytem is rather "big" compared to the size of the motor, that everything else will be OK. You can spend as much time as you want checking out other potential problems and details. But sooner or later there comes a point in every project where you have to shoot the engineer and start construction.

 

[Ahr35181]

jbartos,

I myself have laughed off your ridiculous replies to several of my threads. After reading this thread I now know I'm not the only one!!!

Are you gonna retire after you ten thousandth posting?? This will stop a lot of confusement all round!

Chill out & have a BUD!!!!!!

Alan

 

[jbartos]

Suggestion to skogsgurra (Electrical) Oct 21, 2003 marked ///\\jbartos,
I think that your endless postings about anything and everything are getting very tiring. And the way you try to "prove" that you are always right are even more so. In this discussion (and many other) you seem to be unable to understand where your limits are.
///Certainly, everyone is entitled to once own opinion and expertise.\\I am sure that you have some expertise in some technical field (power transmission perhaps?) but what you are writing in this is pure non-sense.
///Unconstructive criticism.\\Someone has to put an end to this.
///Dictators.\\\

 

[jbartos]

Suggestion to Ahr35181 (Electrical) Oct 21, 2003
jbartos,
I myself have laughed off your ridiculous replies to several of my threads. After reading this thread I now know I'm not the only one!!!
///I received some oscilloscope traces of VFD outputs that did not look to me as perfect sinusoids. I am basing my comments on many unique observations, papers, and theory, not on hearsays or postingsays.\\Are you gonna retire after you ten thousandth posting?? This will stop a lot of confusement all round!
///I volunteer postings for many reasons, not only one.\\Chill out & have a BUD!!!!!!
///I am not addicted to one particular brand of beer or postings.\\Alan