ABB i-bus KNX Product Manual

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Contents

ABB i-bus KNX Product Manual Manual pdf 105 page image

ABB i-bus® KNX Planning and application© 2008 ABB STOTZ-KONTAKT GmbH 1034.1.2 Control current influenceThe 1-10 V interface operates according to the current source principle.Hereby, the ballast is a current source which generates a constant current.The Light Controller (current sink) represents an electrical end stage, so thatthe voltage value corresponds to the required dimming setting. The outputstage of the Light Controller output has been designed so that it cancounteract a maximum control current of 100 mA and generate a controlvoltage of 1 V on the ballast. At a 1 V value the minimum brightness whichthe ballast can set results.If the number of ballasts produces a current greater than 100 mA, the LightController output is no longer in a position to reduce the voltage on theballast to 1 V. In this case the minimum dimming value of the ballast cannot be set.The same problems can occur if the control line is too long or if its cross-section is too small. In these cases the resistance and accordingly thevoltage drop on the line is too large, so that the actual control voltage onthe ballast does not correspond to the required voltage value.The control current generated by the ballast depends on the type andmanufacturer of the ballast. Typical currents are between 0.4 and 4 mA.If an average control current of 2 mA is assumed, 50 ballasts can beconnected to a Light Controller output.With a cable cross-section of 0.8 mm 2 a simple control line length of 70 mis possible from the Light Controller to the ballast, or at a cross-section1.5 mm2 100 m is possible from the ballast to the Light Controller.An open control line causes a voltage drop of 10 V on the ballast and affectsthe maximum brightness of 100 %.A short-circuited control line allows the voltage to collapse and the minimumdimming value of the control device is set.The polarity must be observed when the control line is connected. If thepolarity is reversed, the ballast can not be dimmed and the minimumdimming value is set.