multisim simulation

Discussion in 'The Projects Forum' started by andy11221, Feb 17, 2015.

  1. andy11221

    Thread Starter New Member

    Feb 17, 2015
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  2. crutschow

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    You generate a schematic diagram in Multisim Workbench that matches that shown in your referenced schematic.
    For the thermistor TH1, you can use a variable resistor (pot) with the wiper connected to one end of the pot.
    The pot wiper position (resistor value) is controlled from the keyboard.
    When finished you click the simulate switch to simulate the circuit while monitoring the output.
    Adding the optional LED circuit shown will help indicate the state of the output relay.
     
  3. andy11221

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    Feb 17, 2015
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    Do you have multisim use?
     
  4. crutschow

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    I have a very old copy of Electronics Workbench which is now incorporated into Multisim.
     
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  5. andy11221

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    Feb 17, 2015
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    Oh right i was going to ask if you could simulate it on multisim and text me a pic. Would be very much appreciated.
     
  6. crutschow

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    Better that you attempt it yourself and then come back with any questions if you have a problem.
    You won't learn much if you just look at something I did. :rolleyes:
     
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  7. andy11221

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    Feb 17, 2015
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    I'll give it a try. Could you please explaine how the circuit operates
     
  8. crutschow

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    The circuit uses a 741 op amp as a comparator.
    The 741 output is at its maximum voltage when the plus (+) input is more positive than the negative (-) input
    and the output is at its minimum voltage when the plus input is more negative than the negative input.
    When the 741 output is high it turns on the transistor which actuates the relay, closing its contacts.

    The plus input has DC voltage trip point that is adjustable by the pot P1.
    The minus input varies with the temperature of the thermistor Th1 (whose resistance varies with temperature).

    When the thermistor resistance causes the minus input voltage to be below the trip voltage on the plus input, the relay is energized.
    When the thermistor causes the minus input voltage to be above the trip voltage, the relay is unenergized.
     
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  9. andy11221

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    Feb 17, 2015
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    Thank you very much. Like i said i will give the multisim a try and see if i have any queries about it.
     
  10. crutschow

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    Multisim is more intuitive than most other Spice programs so hopefully you won't have too many problems.
    Try to draw the circuit so it's laid out similar to the schematic shown.
    Good Luck.
     
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  11. andy11221

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    Feb 17, 2015
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    Are variable resistors available on multisim, cant seem to find them
     
  12. crutschow

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    In my old version of Workbench it's in the "Basic" components drop-down.
    You use the potentiometer (resistor symbol with an arrow terminal in its side which is the pot wiper). You connect the arrow terminal to one end of the potentiometer to make a variable resistor.
    The position of the pot wiper (0 is at one end, 0.5 is the middle, and 1 is at the other end) is controlled by the keyboard R key which thus varies the resistance.
     
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