Understand Control Signal Jargon

    Posted on Mon,Oct 24, 2011 @ 10:00 AM

     "On/Off", "Open/closed", "3 Point", "Tri-state", 'proportional modulation", phase cut", "PWM" or "MFT" - what it all means.

    On/Off or Open-Close:  The actuator is able to drive either to its full open position, or to its full closed position.  The same indication is used for spring return type actuators.  Where the actuator will drive to its full open position and spring return to its zero position.  This can also be reversed. 

    3-point, Tri-State, Floating Point: The actuator has both clockwise (CW) and counter-clockwise (CCW) control inputs. One drives the actuator to its open, the other to its close position. If there is no signal (Null point) on either input the actuator simply stays in its last position. 

    Proportional Control: The actuator drives proportional to its control input and modulates throughout its angle of rotation.  This control type is usually a variation of VDC.  Common values are:

          0-10 VDC              2-10 VDC

    It is common to also have a 0-20/4-20 mA output from a controller.  This can be very easily converted to 0-10 VDC or 2-10 VDC with a 500  resistor.

    Pulse Width Modulation (PWM): The actuator drives to a specified position according to a pulse duration, the “length” of signal.  The pulse can originate from a dry contact closure or a triac sink or source controller.  An example of PWM control:

    Time base: 0 to 10 seconds
    Output pulse: 5 seconds
    Actuator position: 50%

    Phasecut: An actuator drives depending on the power result of a remaining wave. This signal type cuts the amplitude of the wave and the actuator recognizes this signal as a proportional movement.


    Multi-Functional Technology (MFT):  This technology was developed by Belimo for incorporation into our damper and valve actuator.  MFT provides the ability to program characteristics of the actuator.  Some of the key characteristics to change are:

          selectable On/Off, VDC, PWM or Floating point

          selectable Running time adjustment

          selectable feedback values

    Belimo actuators are compatible with many control inputs and all direct digital control (DDC) systems. There are many signals to select from with today’s controllers.

    Tags: Technical Tips

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