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3M Surface Capacitive Touchscreen is Not Accurate and Sometimes Freezes

3M Surface Capacitive Touchscreen is Not Accurate and Sometimes Freezes

Overview

Your 3M SCT ClearTek II touchscreen suddenly becomes inaccurate. When an icon is touched, the touch point is some millimetres from the icon. Occasionally the touchscreen freezes up and is completely unresponsive.

Cause

Most SCT touchscreen problems (excluding physical damage) are caused by incorrect integration of the sensor.

Assuming that the touchscreen has been correctly calibrated, this fault may be due to the close proximity of metalwork to the touchscreen.

As the surface capacitive touchscreen relies on grounding via the user’s finger to indicate a touch, placing a metal bezel directly onto the touchscreen glass surface is, in effect, grounding the touchscreen around its entire perimeter. This will cause the touchscreen to under-perform.

In addition, if the touchscreen and monitor are mounted on the machine chassis and the door opens and closes onto the touch sensor, the opening and closing action will also have an adverse effect on accuracy.

 

Resolution / Action

Click here to download the 3M SCT Integration Guideline.

If a bezel is fitted to the monitor, there should be a layer of gasket between the sensor and the bezel.

If the monitor is fitted directly to a metal frame, there should be a layer of gasket between the sensor and the metal frame.

When the controller is powered up, it acclimatises itself to its enviroment which optimises accuracy; if the environment changes during this process (eg opening the machine door), performance will be impaired.

The following is a list of guidelines for integration of a touch sensor with a metal bezel:

  • Please refer to the ClearTek II Integration Guide for complete integration instructions.
  • If your current design has a metal bezel, ensure that it does not directly contact the touch screen. The bezel should be appropriately grounded and very rigid. Use insulating tape or gasketing as a spacer.
  • Be aware that some plastic bezels have conductive paint that could act as a metal bezel, so the same design rules apply in these instances.
  • If there is a conductive door or bezel, send a reset command to compensate for capacitance changes after closing the door. On most enclosures, a reset can be generated using the door open/close switch.
  • ​3M Touch Systems does not recommend metal touch screen mounting brackets. Make sure that any metal brackets are grounded.
  • Use closed-cell foam, single-sided adhesive per the ClearTek II Integration Guide. The seal may be compressed between the bezel and touch screen surface to create a good seal.

Additional Info

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