BECKHOFF DK9222-0310-0010 - Manual (Page 4)

I/O
Bus Terminals
Application Note DK9222-0310-0010
the type of control and the point of the output values within the sine half-wave, the actual control effect will be considerably
stronger or weaker.
The visible light corresponds to the power P supplied to the lamp, which, in the case of AC voltage,of the product of the time-
dependent variables î and û. Due to the multiplication of the two variables, the power is also positive in the negative half-
wave. The momentary values î and û have a different value depending on the point in the mains wave, thus their product, the
power P, is also different at different points in the mains wave. Without an integrated characteristic the step width on the time
axis is constant. The power within the constant step width is not constant, since the amount of space below the sine wave
changes per step. The constant step width is particularly disadvantageous when regulating around the peak of the sine wave:
A step width reduction at 50 % by ±10 percentage points corresponds to a brightness adjustment of considerably more than
20 %. Therefore, the operator is inevitably compelled to adjust more precisely in order to achieve a linear change of brightness.
In practice, it is therefore difficult to achieve adjustment with high repeatability. If controlled illumination of the room is
desired, one is compelled by means of commissioning to trace a linearisation characteristic and subsequently to enter it in the
controller by hand accordingly.
Network-capable dimmers with linearised characteristic
The KL2751 and KL2761 Bus Terminals are universal dimmers with linearised characteristic for the uniform brightness
regulation of lighting elements. Capacitive, inductive and ohmic loads can be connected to the single-channel universal
dimmer terminals. Since the terminals are capable of both types of phase control, they can also be used as power switches
for the control of AC loads, depending on the power requirement of the connected load (KL2751: 300 VA, KL2761: 600 VA).
Furthermore, the terminals can be integrated in any control environment via Bus Couplers and are thus among the few
currently available network-capable universal dimmers that are not based on the DMX protocol standard normally used for
professional lighting (as of 09/2009).
The terminals offer many advantages to the user and are particularly uncomplicated to handle. As is typical of universal
dimmers, there is no need to exchange the dimmer if the type of load has changed (R, L, C). The terminal recognises the
connected load automatically after switching on the mains supply (not after switching on the consumer!) and applies the
appropriate control principle. Furthermore, the terminal is short-circuit-proof: Without the employment of a short-circuit-proof
dimmer, the fuse must also be exchanged as a rule when exchanging the lamp, since the fuse is also damaged by the short-
circuit when the filament burns out. The short-circuit resistance of the KL2751/61 prevents damage to the fuse, so that no
maintenance work is necessary inside the control cabinet when exchanging the lamp. The terminal is particularly discrete in
the control cabinet because, with a width of only 12 mm, it takes up the space of two conventional rail mounted terminals, like
almost all Bus Terminals from Beckhoff Automation GmbH. It is thus four times smaller than a conventional universal dimmer
for DIN rail mounting. The dimming behaviour of the KL2751/61 is considerably more consistent than that of the conventional
universal dimmer due to the internal linearisation. As opposed to a constant step width, a brightness-dependent step width is
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