Blog posts of '2012' 'September'

Resistive Touch Screen

A resistive touch screen panel comprises several layers, the most important of which are two thin, transparent electrically-resistive layers separated by a thin space. These layers face each other, with a thin gap between. The top screen (the screen that is touched) has a coating on the underside surface of the screen. Just beneath it is a similar resistive layer on top of its substrate. One layer has conductive connections along its sides, the other along top and bottom. A voltage is passed through one layer, and sensed at the other. When an object, such as a fingertip or stylus tip, presses down on the outer surface, the two layers touch to become connected at that point: The panel then behaves as a pair of voltage dividers, one axis at a time. By rapidly switching between each layer, the position of a pressure on the screen can be read.

Resistive touch is used in restaurants, factories and hospitals due to its high resistance to liquids and contaminants. A major benefit of resistive touch technology is its low cost. Disadvantages include the need to press down and a risk of damage by sharp objects. Resistive touch screens also suffer from poorer contrast, due to having additional reflections from the extra layer of material placed over the screen.

IP Protection Class

In many ennvironments electronical devices must stand rough conditions and work for their indetnded period of time nevertheless they are set out to dirt, dust and humidity. IP protection classes define, how and where they can be used without getting a safety risk. Especialy in medical areas the safety is very important for the device and all above for the patients.

The following table shows the different IP protection classes:

 IPCharacteristic 1 for protection against contact IP Characteristic 2 for waterproofing 
 0  No special protection  0  No waterproofing
 1  Protection from solid objects greater than 50mm in diameter  1  Protection from dripping water
 2  Protection from object not greater than 12mm in diamete  2  Protection from vertically dripping water (tilted up to 15°)
 3  Protection from object not greater than 2,5mm in diameter  3  Protection from sprayed water (tilted up to 60°)
 4  Protection from object not greater than 1mm in diameter  4  Protection from splashed water
 5  Complete protectionm against contact, Protection against dust deposit  5  Protection from water projected from a nozzle
 6  Complete protectionm against contact, Protection from infiltration of dust  6  Protection against heavy seas, or powerful jets of water.
 7    7  Protection against immersion
 8    8  Protection against complete, continuous submersion in water.
   9  Protection against the ingress of water form all directions even under greatly high pressure on the housing. (High-pressure/steam cleaner, 80-100 bar)


What is the difference betweenn an Industrial CPU card and an off-the-shelf commercial motherboard?

Industrial CPU cards are designed to survive the harsh environment, where extremes of temperature, vibration and electrical noise could easily damage 'normal' system components. Commercial motherboards are not designed for such environments.

Motherboards come cheap, but you (don't) get what you (don't) pay for:

  • poor grounding, shielding, isolation. Poorly designed motherboards do not provide an adequate multi-layer design for effective signal routing, ground and power plane separation for EMI/RFI compliance. What are we really measuring here?
  • low reliability due to cheap
    • electronic components (e.g.: using normal electrolytic capacitors, the heat inside the chassis will cause the electrolyte to dry up over time. This in turn may cause shorts, erratic system behavior and so on)
    • mechanical components (e.g. connectors with a short insertion life or improperly coated pins, therefore subject to poor electrical continuity over time).

As mentioned previously, industrial CPU cards minimize system downtime (e.g. passive backplane cards all comply to standard mounting specs), and allow an easy upgrade path as newer technology becomes available.