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Old 08-25-2007, 02:43 AM
ItsPeteReally ItsPeteReally is offline
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Join Date: Feb 2006
Location: Ipswich, Suffolk
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Originally Posted by Phast SVX
Very succinctly put sir.

He was right about the ballcock, but missed the fact that the feedback from its position was the only 'function of control', whatever that means. There is no attempt to measure and act upon the either the input water pressure or the output water flow.

Similarly with the pendulum, which works solely as a feedback mechanism. Without it, the hands would rotate at a speed related to how tightly the mainspring was wound up. Once again the pendulum is the sole 'function of control'.

Lastly he seems to think that the oven thermostat is an input control sensor, like the MAF, rather than an output measurement sensor, like the O2 sensor!

The oven has no idea of how much energy is being fed in, what the thermal load is inside the oven, or what the external air temperature is, all it knows is the feedback from the internal temperature sensor, and uses that to control the input energy source. The oven has no MAF equivalent, it doesn’t need one!

Finally he mentions the AVC (more properly called AGC) in a domestic radio. Not only does it not act as he said it does; if it did pianissimo sections would be as loud as fortissimo sections, flattening the dynamic range of the music, but also, it doesn’t work as he describes either.

What it actually does is attempt to keep the amplitude of the carrier wave constant so that powerful nearby radio stations are as subjectively as loud as distant weaker radio stations. All of this control is achieved by feeding back the rectified carrier wave voltage, which is extracted before the volume control, to control the gain of the radio-frequency stages. The volume control plays no part in this process at all, and certainly is not ‘the controlling component’. The AGC system is totally unaware of the volume control setting.
I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be.
Sir William Thomson
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Old 08-25-2007, 09:45 AM
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Trevor Trevor is offline
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Join Date: Feb 2002
Location: Auckland, New Zealand
Posts: 5,152
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Pete, damn it man, read understand and digest what you read. Having done that write accurately when you reply. Or is it that a ploy whereby you hope that ever increasing confusion will conceal your errors?

It is interesting that you are not willing to face the music and slyly reply by way of back handed sarcastic remarks directed towards a third party.

You show that you are unable to grasp that the set point (the correct term within control engineering), can be either fixed or adjustable. Setting this point is the control function. Any following feed back loop does no more than adjust subsequent variables in order to maintain the set point. It can not and dues not alter the set point. It does not control, it is confined to making adjustments after the method of control has set the required functions/level, whatever.

In respect of a ball cock the controlled parameter (set point) is confined to the level of water. Control here is reliant on adjusting the position of the float. Move same and you control the water level. Why in hell are you referring to water pressure or flow? Trying to shuffle sideways?

Now we have a pendulum. Previously we had a very strange clock which in your words comprised, “pendulum and escapement in a simple mechanical clock.” Some clock ! now on the scene is a new type of pendulum --- “which works solely as a feedback mechanism”.

A mechanical clock can be and is controlled via readily available adjustments. The degree of control is limited as the clock is designed accordingly. The pendulum weight can be moved up or down. The spring within an escapement in effect lengthened or shortened by means ot a lever. This is how the mechanism is controlled.

Once the controls have been set, i.e. the set point established, the pendulum simply acts as a simple governor NOT as a feed back loop. Check on the governor within a clockwork toy. In a clock, what could be misconstrued as a feedback loop, is the mechanical system catering for changes in temperature. Even here there is no feedback and the parameters are predetermined and set.

As for the oven. The knob on the thermostat is the means of control. The feedback function only maintains the set point and is not a means of control. What the thermostat “knows” and is required to “know” as you put it, is the position of the knob, i.e. the controlling parameter (set point) as adjusted/set by the cook.

AVC/AGC Smart ass, in my part of the world it was/is known as automatic volume control. This description having been decided upon so that it could be publicised as a sales gimmick. Here you inject more sarcasm and show that you are unable to read and assimilate. You endeavour to twist my words in an effort to prove an error exists. My words:-

“An electronic loop adjusts amplifier gain in spite of variations in the input signal.”

I was intentionally not specific so as to simplify the description of my example. I WAS IN NO WAY IN ERROR. Your statement is devious and dishonest.

You state:-"Not only does it not act as he said it does; if it did pianissimo sections would be as loud as fortissimo sections, flattening the dynamic range of the music, but also, it doesn’t work as he describes either."

You go on with a lecture by way of showing your perceived abilities. I sucked eggs when the process involved auxiliary plates within a multi purpose vacuum tube.

You imply that I referred to an adjustment within the audio stages. I did not suggest that the adjustment involved is in any way related to, or is intended to cover anything more than very short term fluctuations within the RF input. At no point did I refer to an audio signal. Your attempt to discredit me is stupid, as well as devious.

You do nothing more than argue incorrectly over side issues involving only examples put forward, rather than involve yourself in what is the essence of this thread. Namely that your proposals are not viable.

In respect of the SVX engine management system, manual control is initiated via the throttles. As a result air flow becomes altered due to the engines response. The resulting airflow then initiates overall control of the engine via the MAF.

The MAF senses the engines requirements in respect of air and continually fixes a constantly varying set point accordingly. The MAF is the first point of control, within an integrated automatic system incorporating multi inputs.

If the MAF signals maximum flow when due to modifications, this is not in effect the real situation and all that follows is out of order and in error. Adjustments should be initiated relative to airflow and all parameters setting combustion issues set/varied accordingly by this the first means of control.

Any feedback loop adjusts to maintain set levels as are dictated by the MAF. These adjustments via feedback, involve a delay. Altering the loop must distort the application of control from the MAF. This proposed alteration comprises the essence of my argument whereby I disagree.

Messing with the feedback loop is not an acceptable method of adjusting for errors originating from the MAF, i.e. the first control with in a control system. This proposed arrangement can only result in distortion, and a never ending requirement to compensate for the errors which will occur. Furthermore there are several other related inputs to the ECU which if applied in conjunction with a distorted signal must add an increasing factor of errors.
Trevor, New Zealand.

As a child, on cold mornings I gladly stood in cowpats to warm my bare feet, but I detest bull$hit!
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