Re: Problem with a fan controling by the inverter ;/

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

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.


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.



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.


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).


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.



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.



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 :-) 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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