0-10v to 2-10v

Discussion in 'The Projects Forum' started by ol'trusty, Jul 3, 2014.

  1. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    Hello
    In the place I work we purchased 2-10v actuators but have 0-10v controller.
    The easiest would be to change the actuators bot I was wondering if someone here has an idea...
    What I need is a circuit that will amplify a 2v input to 3v but wont amplify any input greater than 3v. doesnt have to be precise.
    I have 24vac to work with.


    For those who are interested it is an actuator of a water valve on an air conditioning system. What is happening now is that when the controller outputs 1V for example (when temerature is around setpoint) instead of letting through a bit of water it doesnt do anything at all.
    I can set the controller to put out 5 steps of 2 volts but in the lowest step it still wont do anything. That is why I was thinking maybe it can be solved.
    And that is why I dont need it to amplfy above 4V

    thanks for reading
    :cool:
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Would it work to add a small fixed offset to the signal, like 0.5V?
     
  3. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    What is the current rating of the actuator/controller.?

    E
     
  4. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    attn:crutschow
    0.5 offset might not give the desired result. it might be to small of a signal at 2.5V.
    Also I dont know the consequences of feeding it with 10.5v at maximum working voltage.
    I think ideally 3.5V would have the system in "cruise mode"

    attn:ericgibbs
    I am not sure (i can check the datasheets) but just to be clear it draws operational current from the 24vac the 0-10 is just reference voltage.. sorry if I misunderstood and I can check if it makes a differnce

    thanks
     
  5. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    Not having seen the d/sheet for the actuator does it it have its own internal drive amplifier and the controller sends a 0 to 10Vdc low current control signal.?

    E
     
  6. ol'trusty

    Thread Starter Member

    Sep 9, 2009
    48
    0
    yes exactly. simply a control signal
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    A 12V linear regulator (7812 type) with a shutdown input would work. The shutdown input would be driven by a comparator to keep the regulator off when voltage is less than 2 V. Above 2V the output follows the input.
     
  8. ol'trusty

    Thread Starter Member

    Sep 9, 2009
    48
    0
    hey papabravo
    I dont quite understand what you are suggesting.
    what do i gain with the 7812 ? and how does it bump up the voltage ?
     
  9. inwo

    Well-Known Member

    Nov 7, 2013
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    That's what I'm thinking. Add 2v offset.

    I'd bet the valve isn't linear on the top end. Hitting wide open a little early won't matter.

    12 volts isn't going to hurt. If worried it could be clipped at 10v.
     
  10. crutschow

    Expert

    Mar 14, 2008
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    Below is the simulation of a circuit that uses a window comparator to add an offset to the signal between about 2V to 3.5V. Is that what you want?

    Note that I didn't show how to generate the +12Vdc. You could add a rectifier, filter, and voltage regulator to generate the +12Vdc from the 24VAC.

    Offset.gif
     
  11. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    how would i clip it to make sure it doesnt pass 10V?
     
  12. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    attn: crutschow
    nice one. what aould i need to add to turn my 24 vac to 12vdc that this circuit runs on?
    some capacitor and the 7812 i assume? remind you that 24vac is what i need to work with because i would put this circuit near the actuators (in their connection box)
     
  13. Papabravo

    Expert

    Feb 24, 2006
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    It doesn't bump up the voltage it outputs 2-10 volts for a 0-10V input.
    It is well know that a linear regulator output will follow the input when the input is less than the regulated output voltage. A 7812 will output 0-10V for a 0-10V input. A 7812 with a shutdown input can be used to output 0V when the input is between 0V and 2V.
     
  14. crutschow

    Expert

    Mar 14, 2008
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    The circuit takes less than 5mA so a linear regulator will dissipate very little power. You could use a 1N4848 diode (or similar) connected to the 24VAC, a 100μF capacitor to ground, and a 10V zener diode to feed the input of the 7812. You need to put the zener in inverse series (back-to-back) with the diode to drop the voltage safely below the 35V maximum input rating of the 7812.
     
  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    I'm confused as to exactly what voltage range you actually need?
     
  16. ol'trusty

    Thread Starter Member

    Sep 9, 2009
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    attn: papabravo
    What output will I get at 2v ?

    attn: crutschow

    "quote:You need to put the zener in inverse series (back-to-back) with the diode to drop the voltage safely below the 35V maximum input rating of the 7812."

    wouldn't the ac voltage become 34vdc ? I multiplied by sqrt2.
     
  17. ol'trusty

    Thread Starter Member

    Sep 9, 2009
    48
    0
    I might of confuse things a bit . but to make it simple I need that a 2v output from controller will give 3V to actuator because the actuator still doesnt react at 2v being a 2-10v
     
  18. crutschow

    Expert

    Mar 14, 2008
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    True, which is too close to the 7812's maximum rating of 35V for good reliability. That's why I added the series zener, to drop it to about 23V.
     
  19. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Assuming your actuator control input is high impedance (>10k), here's one way you could get a 3-10V (approx) output without the use of an opamp, albeit there's a constant 3V output when the controller is in the 0-3V range:
     
    inwo likes this.
  20. ol'trusty

    Thread Starter Member

    Sep 9, 2009
    48
    0
    attn:alec_t
    I really like that your design does the job very simply!
    And yes this is what I need in order to not replace the actuators.
    What would need to be changed if I needed to tweek the output a bit? Can I use a potentiometer in the circuit ?
    I just have to check the impendance because I really am not so sure about that, hoping though.
     
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