If I plunk in a capacitor for power factor correction, would this be 'open loop control' of my power factor correction system? What if I switch capacitors in and out based on time of day? Or turn a light on and off based on time of day? Maybe some simple things can be considered open loop control.
j
This seems to me to be mere quibbling about the definition of closed vs. open loop. As I see it, switching capacitors in or out (or adjusting the field rheostat of a synchronous capacitor) is no more or less open loop than flipping the wall switch to turn lights on and off or positioning an accelerator to maintain a constant speed as the grade changes. You can com down on whichever side you like, but I choose to call cruise control closed loop, and normal use of a gas pedal open loop.
Jerry
On Tue, 08 Nov 2005 23:06:05 -0500, Jerry Avins proclaimed to the world:
Actually normal use of a gas pedal, eg a person controlling the car's speed would be a closed loop too as the feedback and adjustment is coming from the eye on the speedo, brain and adjustment of the pedal with the foot.
In this situation an open loop would be if the driver just pushed the pedal to position A, assuming that would result in speed A. Open loop always assumes and is blind to error.
Driving like this might work poorly if you drove on flat ground. I used to have an old truck with a 390 ci engine geared low. You could press the pedal and it would stay at one speed pretty well but consider that the load on the engine was a very small percentage of the available power.
An example of a near perfect open loop system although not as obvious would be a gearbox. You assume that an input rpm will result in an output rpm based on gear ratio. This is not for sure though. For instance a shaft key could be sheared allowing a gear to slip on a shaft.
On a side note, I live in mountains and many cars I have had have a hard time staying at speed whether on cruise control or not. This is a result of car manufactures making the gear ratio high to maximize mileage in test conducted on flat ground. In real situations in the mountains the gearing results in the tranny shifting back and fourth or the driver shifting out of overdrive which ends up making the mileage worse. The car manufacture actually provide differently geared transmissions for cars that are sent to dealers in mountainous areas. Unfortunately if you buy used cars, many of them come from flat, low regions because they do not use road salts and the used cars are not rusted.
Be well,
HoP
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Jerry Avins wrote in news: snipped-for-privacy@rcn.net:
I don't think there's much to quibble about definition-wise. If you are somehow monitoring the actual output, and making adjustments to the input (or system) based on the actual output, the loop is closed. The examples of switching capacitors in or out are open loop, as you are making adjustments based on some model of the output that does not account for disturbances.
As for the human on the gas pedal, the human is part of the loop, thus it's closed loop. The observer might not be perfect, and there might be delays, and the feedback gain may change, its still a feedback system.
Scott
To operate early steam engines, a worker pushed a valve one way when the piston teach one end of its stroke, and pulled it back when the piston reached the other end. Two of James Watts inventions were the slide valve driven by an eccentric, and the flyball governor to control a throttle valve that maintained constant speed despite changing load.
In my classification scheme, Watt's inventions created the transition from open to closed loop. You can call them both closed loop if you prefer, but that makes discourse more difficult. When there is no one to hear a tree fall, it makes noise or not depending on how one chooses to define noise.
I believe we agree that a pendulum clock is an open-loop device, despite a human deciding that it needs winding. How do you classify a radio? It is, after all, the listener who regulates stations and volume.
...
Jerry
Jerry Avins wrote in news:MfydnWulIqhdm- snipped-for-privacy@rcn.net:
If the radio uses a PLL tuner, it is closed loop. The human provides the command.
And don't forget AGC in an AM radio. That's a very classic use of closed-loop control.
I think the difference is that when I sit in my car I think of the _car_ as being open loop. When my wife rides with me she things the system of my car and me is a (possibly deeply flawed) closed-loop system.
And AFC in FM radios. (As one station manager said to an annoyed listener who claimed that his station drifted, "Madam, nowadays you can buy a tuner that drifts to follow the station." He suggested that she patronize my store, and that I would explain the details to her.)
Can I create a closed loop by hiring somebody to watch the zero-center tuning meter and make the necessary tweaks?
Jerry
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Ah, connubial bliss! So when I watch what I'm doing while driving nails, the system of me and hammer is closed loop. I can buy that in the abstract, but the concept of a hammer consisting of a steel head and a hickory handle as a closed-loop device would be rather puzzling if we hadn't been having this conversation. Knife, fork, pen, broom: all closed loop? If you choose to say so, fine. Just be explicit.
Jerry
I would say that you _and_ the hammer is a closed-loop system, but just the hammer is a thing; really neither open- nor closed-loop because it doesn't do anything by itself (unless you drop it).
Problems in maintaining stability in human-in-the-loop systems are of some concern in high-performance aircraft manufacture; you can have an aircraft that by itself has totally stable dynamics yet has enough delay from stick to airframe motion that it'll go unstable with any but a really good pilot in the hot seat.
An acquaintance of mine was the software lead on the flight control for a Saab fighter that crashed at the Paris air show due to a combination of a test pilot who wasn't as manly as he thought and a slipped digit in a control rule specification. He got to watch a movie of the "landing" when they still thought it was a software bug, including the part where the wings fell off right after the pilot put the balls to the wall trying to abort. No spectators were seriously injured, the pilot walked away with a broken arm.
For some reason that guy's a demon for software quality...
If closed- or open loop doesn't apply to a hammer, does it apply to a scooter? If not scooter, to a bicycle? Motorcycle? Car? A harbor buoy "automatically" rises and falls with the tide. What about that? I think it's best to keep a definition's "region of applicability" narrow, especially a technical one.
Unless we create a a metaphor, it's isn't usually helpful to classify a tool and something -- human, animal, or robot -- using it as a closed loop. Broadening the notion that way in everyday discourse dilutes its meaning too much. If we were to call most activities closed loop, we would lose useful distinctions.
Jerry
Tim Wescott wrote in news:hcqdnYivVKgO2-_eRVn- snipped-for-privacy@web-ster.com:
Back in the day, we had a lab where we turned a pot to keep a line on a grass chart recorder on zero in the presence of disturbances. Gain and delay were changed in "secret" ways to show us how easy it was to go unstable.
On Wed, 09 Nov 2005 09:25:01 -0500, Jerry Avins proclaimed to the world:
When in the navy the ship I was on had a steam driven bilge pump that worked this way. It took a bit of skill to get the thing going, draining the condensate and tripping the slide valve to get that first stroke. Dangerous too. I saw several guy just about clip finger off when the piston went and the slide tripped over while his hand was still in the area.
Be well,
HoP
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On Wed, 09 Nov 2005 13:37:28 -0500, Jerry Avins proclaimed to the world:
Yes, but not me.
I still maintain that I am being accurate and not nit-picky. ;-]
Be well,
HoP
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On Wed, 09 Nov 2005 10:57:33 -0800, Tim Wescott proclaimed to the world:
Ever seen the video of the early Raptor tests?
Be well,
HoP
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On Wed, 09 Nov 2005 15:01:39 -0500, Jerry Avins proclaimed to the world:
I think the opposite here. The loop is closed if there is feedback and correction whether this is by human or not. If I go in the direction you suggest the definition becomes blurry. I like clear vision.
Another subject that this reminds me of is the difference between analog and digital. Quantum mechanics suggest that everything is digital but who has a microscope powerful enough to observe this.
Be well,
HoP
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That sounds to me like a single-piston direct-acting Worthington pump. The one I used would start by itself when steam was applied, but not all did. Have you ever watched a duplex (dual-piston cross-coupled) model work? Nothing rotates, but it's clearly two phase.
...
You could as well argue that everything is analog. Quantum mechanics aside, one can't go from here to there without passing through between.
Jerry
On Wed, 09 Nov 2005 17:46:35 -0500, Jerry Avins proclaimed to the world:
Yes that is exactly what it was. The site even lists it as being used as a bilge pump. The dead spots they talked about is accurate. If it stopped at the "wrong" place you had to take a crow bar and move it by hand to get it going. We had a name for it based on the sound it made running that escapes me right now.
Good site. Howstuffworks has some good animations of pumps.
I'm thinking of building a version of the Stanley Steamer for a hobby one day or perhaps using a re emergent steam turbine. This is a rather rare type of turbine that has high torque at low rpms. It might be a nice thing to have if gas becomes hard to find.
Be well,
HoP
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