Universal Isolated Dimmer
Universal Isolated Dimmer
The isolated dimming control panel, allows dimming control of multiple instruments and lamps from one control point, giving even control of the brightness levels. It replaces old systems with multiple knobs or multiple banks of potentiometers. Especially in systems with different brightness levels.
How the old systems worked:
Each circuit is connected to a common variable voltage supply, then grounded to illuminate the devices. The common supply usually travels through each device is not isolated. So any faults can be passed on to the other device, resulting in damaged equipment.
The new system:
The isolated system has six channels that are separated but controlled by a single, level adjusting knob (potentiometer) or momentary switch (push buttons).
Each channel can drive a 1 amp 24 v pulse width modulation for lighting instruments. If more channels are required, then extra panels can be coupled together with the first acting as the master control.
Each channel has a maximum and minimum brightness adjusting knob.
The other two channels also have a non-lar adjustment for instruments or systems that require it.
As each channel is fully isolated, they can operate individually on either the supply circuit or the grounded circuit of any systems to which they are fitted.
Polarity of the circuits must be observed correctly for the dimming to work. However, incorrect connection will not damage this device.
The output frequency is approximately 100Hz. This is low enough to eliminate interference but high enough to maintain luminosity without flickering. The output includes a small EMC filter, however, systems designers should consider the EMC issues alongside the equipment to which the unit is to be connected.
The power supply is fitted at input and between connecting panels to avoid interference issues.
Using the four corner holes mount the unit to a firm dry surface within a dry compartment. It is 225 x 140mm and needs about 40mm depth. Mounting holes are 4.0mm spaced 210mm x125mm.
The power supply powers the dimming control system. It is important this supply is always maintained so should be from a battery backed up 24V DC supply rated at 1A.
Three options for control exist:-
1. Potentiometer Connect a potentiometer with a value between 1K and50K to the terminals as shown on the connections. Use three core cable, or twist three cores together. Set the link for ‘POT CTRL’
2. Momentary Push Button Connect a momentary push button between the ‘Dig In’ terminals and the 0V terminal, use twisted pair cable. Set the link to ‘PB CTRL’. Each press of the button will cycle the dimming through five levels of brightness. Press and hold the button for approximately 3 seconds to go directly to maximum brightness.
3. Serial input from first card. This is used when additional output channels are required, each card should be supplied from the same 24V DC battery backed up 1A supply. The potentiometer or push button control are connected to the first card. Then connect the ‘Ser Out’ from the first card, to the ‘Dig In’ on the next card using twisted pair. Link more cards in the same manner to provide the number of output channels required. Set the link on each additional card to ‘Ser Ctrl’.
There are six output channels, each is fully optically isolated from other channels and from the control supply. Each output uses a simple power mosfet transistor with simple EMC filter and provides dimming control by pulse width modulation at approximately 100Hz and can easily support a 1A 24V lighting load.
It should be noted that power mosfet transistors by the nature of their construction have an intrinsic power diode, this means that the + and – labels must be adhered to when connecting the illumination circuit, however if connected in error damage will not occur, but the lamps will run at full brightness.
Simply think of the output as an adjustable brightness switch and wire in line with each separated block of lamps for the respective channel. Lamps may need to be separated for channels based on their control source i.e. engine, steering thrusters etc., but may also need to be separated based on colour.
Adjusting output channels
Each output channel has adjustable trim pots, maximum brightness via the ‘FULL’ trim pot, minimum brightness from the ‘Dim’ trim pot, and two channels have an adjustable mid range ‘Mid’ trim pot.The Dim trim pot controls the pulse width for minimum brightness, the Full trim pot controls the pulse width for maximum brightness, in between is controlled by the dash board mounted dimming pot, or push button 5 step control on a linear relationship, EXCEPT for two channels which have the ‘Mid’ trim pot able to create knee point in this linear relationship which is sometimes of use for non-linear systems, when this feature is not require just set it to the middle position.The simplest way to set the system up is to set the master controls (dash pot or push button) to maximum brightness (best on a bright sun lit day) and adjust each ‘Full’ trim pot to the point where no increase in brightness is seen in display lamps. Then set to Dim at master control, best on a dark night, and adjust the ‘dim’ trim pots so that the display lamps are just lit. In most cases leave ‘mid’ in centre position. Now trial the master control pot or push button and view that your dash panels lamps dim in unison and similar brightness levels. Fine adjustments may then be required to trim pots or mid pot if a set of lamps are not linear (Note: non linear lamps must be on a channel with ‘mid’ trim pot.