Announcement

Collapse
No announcement yet.

"Fuzzy Logic" - what is it? - in real and layman's terms - please

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • "Fuzzy Logic" - what is it? - in real and layman's terms - please

    We had a replacement (new) space heater (natural gas) space heater installed recently.

    The temperature is not intuitive as was the case previously. The installer said it was controlled by "fuzzy logic" (FL) rather than the previous incremental temperature setting.

    What is "Fuzzy logic"?, how does it work? - in both the layman's/user's and technical terms - please.

    Here are some "Google" responses:

    https://en.wikipedia.org/wiki/Fuzzy_logic

    https://www.google.com.au/search?q=g...#q=fuzzy+logic

  • #2
    It uses digital logic rather than analog PID.

    "FL incorporates a simple, rule-based IF X AND Y THEN Z approach to a solving control problem rather than attempting to model a system mathematically."

    how is fuzzy logic different than conventional controls?

    Comment


    • #3
      Sounds like the computer equivalent of new math.
      mark costello-Low speed steel

      Comment


      • #4
        Originally posted by MTNGUN View Post
        It uses digital logic rather than analog PID.

        "FL incorporates a simple, rule-based IF X AND Y THEN Z approach to a solving control problem rather than attempting to model a system mathematically."

        how is fuzzy logic different than conventional controls?
        Thanks sincerely MTNGUN as your explanation and the link you provided got me off to a very good start.

        Fuzzy Logic makes a lot more sense and accords with what we have on the temperature control on our new gas space heater - so setting the temperature is a lot easier.

        Comment


        • #5
          It was a "buzz word" in the 80s... haven't heard it much since then.

          Comment


          • #6
            So how does it make setting the temperature easier?
            The old way was to set the knob somewhere between
            warm and hot and take a few showers and readjust it
            if needed. How can they improve on as simple as that?

            -Doozer
            DZER

            Comment


            • #7
              What lakeside53 said.

              Our use of the term was slang and had little to do with what MTNGUN stated (guess at some level maybe, maybe derived from it) more to do with trying to use general logic (not math logic) that was of questionable provability or a "proof" that had some key point that was grey or obscure and so either difficult to understand or questionable generally to the point of being almost nonsensical.

              Comment


              • #8
                To some degree, it replaced exact setpoints with ranges, and the ranges didn't necessarily have the same responses.

                You can have a temperature setpoint, say 200F. Then if the temp is over 200F, you cut off the heat, and if it is below, you turn on the heat full. That's standard old mechanical thermostat behavior, that may be also implemened by a microcontroller. Two conditions, temp is either "too hot", or "too cold", heat is either "on" or "off".

                The fuzzy logic version of that might incorporate the same 200 setpoint, but measure the actual temp, not just have an "above" or "below" decision. Then if the temp is 195F, and rising fast, the heating power may be reduced. If same 195F but rising slowly, keep it at max. Same above, if at 202F and rising fast, cut heat off, but if at 202 and rising slowly, reduce heat. Similar on the way down.

                You have "much too cold", "a little too cold", "a little too hot", and "much too hot". In response you can shut of heat, reduce heat, turn it on a little, or turn it on full. Instead of hard "black and white" logical decisions, you have a "gray area" of "kinda sorta", a "fuzzy" area. Hence "fuzzy logic".

                The idea is to avoid abrupt decisions, replacing them with more choices that are condition dependent, to make the changes smoother, with less oscillation around the setpoint. Replacing "hard" logical decisions with partial actions, "reduce heat" instead of "turn off heat". Same as you would do if the pot is boiling over, You do not shut off and turn on full, you turn it down until it simmers nicely.

                I don't think it has become unused, actually it has become common and unremarkable, and that is why you do not hear as much about it.
                Last edited by J Tiers; 04-18-2016, 08:52 AM. Reason: change fussy to fuzzy
                2730

                Keep eye on ball.
                Hashim Khan


                It's just a box of rain, I don't know who put it there.

                Comment


                • #9
                  Since most household heating systems are not throttleable (they're on or off e.g. "bang bang control") one common technique these days is to for the control to 'learn' the response of the house so that it can reach the desired temperatures in the house at the desired times, and minimize over and undershoot. Typically this is done by using a small microcontroller that has a simple math model of the house; the parameters get initial values and are then adjusted based on measured response of the house. In the morning, the furnace may go on before the programmed time, and depending on the measured overshoot may shut off before the set point temperature is reached. Newer models sense your activity (wifi, lights, etc) and don't require fixed schedules.

                  Fuzzy logic isn't really much of a thing anymore since you have such cheap microcontrollers; you can just measure stuff. Why not go from too cold, ok, too hot to .35 degrees above ideal temperature?

                  - Bart
                  Bart Smaalders
                  http://smaalders.net/barts

                  Comment


                  • #10
                    Sounds like where we previously had "Global Warming" and when that didn't fit the agenda or the models (new math?), we now have "Climate Change".
                    Cheers,
                    Gary

                    Comment


                    • #11
                      Originally posted by gcude View Post
                      Sounds like where we previously had "Global Warming" and when that didn't fit the agenda or the models (new math?), we now have "Climate Change".
                      Not to get off track, but the label "Global warming" was changed because it includes cold spells too. This resulted in too many people disbelieving that there was a problem when they had colder than normal winters in some spots.

                      But back on track...

                      Fuzzy logic was already adequately explained. It used to be explained as " yes, no, maybe" logic. I thought of it as "true, false, I don't know" conditions.

                      Dan
                      At the end of the project, there is a profound difference between spare parts and left over parts.

                      Location: SF East Bay.

                      Comment


                      • #12
                        To use the term Fuzzy Logic in the context of this forum is simple. I tell the wife I NEED to buy another machine/tool and give her my reasons. Her reply is "That sounds like Fuzzy Logic to me."
                        Location: The Black Forest in Germany

                        How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                        Comment


                        • #13
                          in the case of home heating thermostats, many of the analog models had "heat anticipation" built in. This feature was a small heating coil or resistor, sometimes adjustable, in series with the switch contact that used the thermostat current to make a little heat inside the thermostat case. Properly set, this warmed the air inside the thermostat housing at a rate close to the household temperature rise when the furnace was on. This minimized localized overshoot at the heating vents while waiting for the warm air front to travel to the thermostat. With digital thermostats, this "heat anticipation" is the fuzzy logic referred to, and may be "learned" by the thermostat over time rather than having to be manually set.
                          Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                          ~Practitioner of the Electromechanical Arts~

                          Comment


                          • #14
                            Originally posted by Black Forest View Post
                            To use the term Fuzzy Logic in the context of this forum is simple. I tell the wife I NEED to buy another machine/tool and give her my reasons. Her reply is "That sounds like Fuzzy Logic to me."
                            Mine has another version, when I'm right I'm wrong when she's wrong she's right, when I'm wrong I'm right, when she's wrong she's right,
                            Very boulean the truth table is fascinating
                            Mark

                            Comment


                            • #15
                              Originally posted by boslab View Post
                              Mine has another version, when I'm right I'm wrong when she's wrong she's right, when I'm wrong I'm right, when she's wrong she's right,
                              Very boulean the truth table is fascinating
                              Mark
                              Mark there are just a few rules regarding fuzzy logic.

                              Rule1: The woman is always right.
                              Rule 2: If the woman is wrong it is because of the man and he must apologize profusely.
                              Rule 3: The man can only be right if the woman says he can be right.
                              Rule 4: See rule 1.
                              Location: The Black Forest in Germany

                              How to become a millionaire: Start out with 10 million and take up machining as a hobby!

                              Comment

                              Working...
                              X