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Problem with a fan controling by the inverter ;/
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Micha³
science forum beginner


Joined: 21 May 2005
Posts: 14

PostPosted: Tue Jun 27, 2006 6:31 pm    Post subject: Re: Problem with a fan controling by the inverter ;/ Reply with quote

Osoba nazywajaca sie Tim Wescott w liscie z dnia 2006-06-27 16:37
napisala nastepujace slowa:

Quote:
I assume that by "inverter" you mean drive? "Guide ring" sounds like
something that, well, guides, where you must be talking about a variable
orifice.

Inverter - electrical element which can control a drive by changing
current frequency :)

Guide ring - let's tell that's someting similar to orifice.


Quote:
Whether you have a fan running at fixed drive with the airflow
controlled by an orifice or a fixed orifice with the airflow controlled
by the fan drive you're still controlling pressure and flow
simultaneously.

Yes. And this situation was. Now, I'll control a fan speed (by changing
his current frequency) and then I'll be able to control only flow. But I
need to control also a pressure. But how? It this is the main point of
the problem.



Quote:
It seems that what your concern should be (and perhaps
is) is whether you can adequately control your airflow by controlling
drive to the fan.


Correct. That's right.

Quote:

Ultimately you'll have to answer this question on your own, because it
depends a lot on the type of fan, the type of motor, the type of drive
you select ('inverter' covers a lot of territory) and your performance
requirements.

How are you controlling your orifice now?

Manualy. And I need to change it. I need to control flow and pressure
automaticaly - so I want to dismount an orifice and mount an 'inverter'
(connected to the drive of the fan).


Quote:
Does your temperature control
loop generate a position command for a position loop around the orifice,
or does the temperature control generate a speed command for the
orifice, which then runs open loop?

Already I only see temperature on the digital indicator. When the
temperature is too high, worker needs to go down and more turn an orifice.



Quote:
How much fluctuation can you stand
in your flow?

I determin that flow must be about 2 m^3/s, and pressure drop in the
oven form about 800 Pa to 1500 Pa.

Parameters of the fan: V = 10 m^3/s, p = 5kPa.

Now a fan works in his 100% of power. And my parameters (V=2m^3/s and
p=800-1500Pa) are setting up by the orifice. Changing this all I want
to save an electric power (decreasing supply of power to the motor of
the fan) and controll my parametres directly from the fan.


Quote:

Assuming that your fan will have a well behaved flow vs. drive
characteristic, it seems like you'd have a pretty good chance of putting
it in and having it work. So the real question you need to ask is what
fan and motor combination do you need to achieve a flow vs. drive
characteristic that's as good as the fan, motor and variable orifice
combination you have now.

If it were _me_, I'd be saying how big the motor is, what kind of fan it
is (squirrel cage, axial, waving palm leaves, whatever), and what kind
of motor/drive technology (brushed DC with amplifier, brushless DC with
brushless amplifier, induction motor with variable frequency drive).
Then I'd sit back and hope some of the folks on this group who know more
about this sort of thing than I do tell me what's right or wrong about
the proposed choices.

Fan parameters:
n=1460 rpm
V=10,8 m^3/s
P=5300 Pa

type: radial

control: now: motor connected directly to the fan; future: motor
controled by the inverter (electric element which is able to change the
frequency of the current Smile connected to the fan.



I know that motor and fan are redimensioned. As I sad earlier, I only
about 20-30% power of the fan. I can't replace fan to the new - so I
must apply some way to decrease fan power keeping air flow at the level
from the 100% fan power.


--
Michal
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Jerry Avins
science forum Guru


Joined: 03 May 2005
Posts: 534

PostPosted: Tue Jun 27, 2006 7:13 pm    Post subject: Re: Problem with a fan controling by the inverter ;/ Reply with quote

Micha³ wrote:
Quote:
Osoba nazywajaca sie Jerry Avins w liscie z dnia 2006-06-27 15:18
napisala nastepujace slowa:

Micha³ wrote:
Osoba nazywajaca sie Jerry Avins w liscie z dnia 2006-06-26 23:21
napisala nastepujace slowa:

...

Maybe if you tell us more about your constraints and the reasons for
them, we'll be better able to offer specific suggestions.

Ok. I'll try to describe my problem more precisely :)

Already my system looks like this:

--- oven -----> guide ring ---> fan ---
| |
------<-----------burner---<-----------

It seems that the air is circulating in a loop.


Right. About 80-90% of the air is still the same. 10-20% is a 'fresh'
air, which contain oxygen (burner needs it).


[...]

I don't know what you mean by "inverter". Is the pressure in the oven
too high, or too low when the flow is right? If it is too low,
throttle the oven's outlet. If it is too high, throttle the oven's
inlet. Either way, adjust the fan speed to maintain the needed flow.


Well... Word 'inverter' I found in a dictionary. In polish this element
is called as 'falownik'. In english, inverter is a electric device that
can control for an example a rotary speed of the engiine, by the
controlling frequency of the current - ehh.. it's difficult to explain
that - but I believe that you will understand me Wink

It's a good word, but it has too many meanings. I understand now what
your device is.

Quote:
Right. I must adjust a pressure in the oven when the flow is still
constant. So - solve of the problem could be mounting a throttle after
and before the oven? Throttles can be connected with the inverter (which
control speed of the fan) by the feedback loop. Am I right?

At any given flow and pressure combination, one of the throttles can be
wide open. (You may never need it at all.) The relation between throttle
setting and fan speed won't be simple. You may need to experiment and
create a table. Moving one of the controls (throttle, speed) slowly and
the other more rapidly is a way likely to succeed.

I hope that someone who has actually built a system very much like yours
can offer you his/her experience.

Jerry
--
Engineering is the art of making what you want from things you can get.
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Micha³
science forum beginner


Joined: 21 May 2005
Posts: 14

PostPosted: Wed Jun 28, 2006 7:35 am    Post subject: Re: Problem with a fan controling by the inverter ;/ Reply with quote

Osoba nazywajaca sie Jerry Avins w liscie z dnia 2006-06-27 21:13
napisala nastepujace slowa:

[...]
Quote:

At any given flow and pressure combination, one of the throttles can be
wide open. (You may never need it at all.) The relation between throttle
setting and fan speed won't be simple. You may need to experiment and
create a table. Moving one of the controls (throttle, speed) slowly and
the other more rapidly is a way likely to succeed.

Well, maybe this is a solve of my problem, but - it's similar to the
situation that I've already: a manual guide ring (it may be called as
throttle) installed befor a fan. So, here an inverter isn't as much
needful ;/


Quote:

I hope that someone who has actually built a system very much like yours
can offer you his/her experience.

Anyway - thanks you for your time and help ;)

--
Michal
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fulliautomatix
science forum beginner


Joined: 01 May 2005
Posts: 34

PostPosted: Wed Jun 28, 2006 12:54 pm    Post subject: Re: Problem with a fan controling by the inverter ;/ Reply with quote

Micha³ wrote:

Quote:
How are you controlling your orifice now?


Manualy. And I need to change it. I need to control flow and pressure
automaticaly - so I want to dismount an orifice and mount an 'inverter'
(connected to the drive of the fan).


Does your temperature control loop generate a position command for a
position loop around the orifice, or does the temperature control
generate a speed command for the orifice, which then runs open loop?


Already I only see temperature on the digital indicator. When the
temperature is too high, worker needs to go down and more turn an orifice.

Doesnt seem to be that you are too concerned with pressure, just
temperature control via air flow regulation?

A good inverter (VF drive), eg Invertek, Hitachi, will offer the option
of PID control to a given set point - usually motor speed fed back from
a shaft encoder

But if the drive were fed a set point in a form it understands - perhaps
via a temperature-frequency converter or something - surely this would
act to control temperature via fan speed
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Jerry Avins
science forum Guru


Joined: 03 May 2005
Posts: 534

PostPosted: Wed Jun 28, 2006 3:07 pm    Post subject: Re: Problem with a fan controling by the inverter ;/ Reply with quote

Micha³ wrote:
Quote:
Osoba nazywajaca sie Jerry Avins w liscie z dnia 2006-06-27 21:13
napisala nastepujace slowa:

[...]

At any given flow and pressure combination, one of the throttles can
be wide open. (You may never need it at all.) The relation between
throttle setting and fan speed won't be simple. You may need to
experiment and create a table. Moving one of the controls (throttle,
speed) slowly and the other more rapidly is a way likely to succeed.

Well, maybe this is a solve of my problem, but - it's similar to the
situation that I've already: a manual guide ring (it may be called as
throttle) installed befor a fan. So, here an inverter isn't as much
needful ;/

...

Assuming that the flow is held constant by varying the speed of the
blower -- that's what the inverter is for -- the pressure in the furnace
can be raised by throttling its outlet, or lowered by throttling its
inlet. There's not much else available to be controlled.

Jerry
--
Engineering is the art of making what you want from things you can get.
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