LCD diplay problems

[tipster]

I have several TMD+1616 PLC's on which I am using the 4 x 20 LCD displays (purchased through TRI-PLC). all are wired according to specs in regards to the current limiting resistor and using the supplied interface cable.
  My problem is this,all of these units will periodically have diplay problems which usually consist of a complete black (blocked out) screen or a blank diplay altogether.  If On-line monitoring is done then the PC display is correct and the PLC always performs it's tasks even in this condition. A master reset function or a reset from on-line monitoring will not clear the display,the unit must be powered down. this usually occurs at least every other day on all PLC displays.  
   Any thoughts or suggestions?

[support]

If this is happening to all the LCD, then it appears that the LCD display is affected by switching noise in your panel. It is important to ensure that the LCD cable not be bundled together with high voltage wire in the same conduit. There are  only 5V high impedance signals on the LCD cable and switching of inductive loads on the 24V or 120V wire can impose enough coupled electrincal noise to affect the display.

You may want to shield the LCD cable using some aluminium foil with grounding. Also ensure that you follow good electrical wiring rule by providing flyback diodes or varistor to all solenoid or contactor to snub the inductive back EMF. Although the drivers on the T100MD1616+ has built-in back emf diode to protect itself,  the cables linking the output driver to the load can still induce large enough voltage to affect the LCD display.