What are the criteria for IR touch screens for reliability under solar interference?

 

An infrared (IR) touch technology is a method of selecting an arbitrary wavelength (IR transmission wavelength) from an infrared wavelength of 700 nm to 1000 nm. It also detects touch by only sensing the IR transmission wavelength in the receiver. This is a simple and reliable touch technology.

However, the infrared wavelength used here is located within the broad optical spectrum emitted by the sunlight. If the infrared light is added to the receiving part of the IR touch sensor module with the IR transmission wavelength, the touch sensing algorithm causes a touch error. Therefore, we have to analyze how the sunlight interferes with the IR touch sensor. Measurement methods and regulations are necessary for these issues.

In the IR touch technology, an IR transmitter is arranged on one side and an IR receiver is arranged on the other. The IR transmitting element and the receiving element may be arranged alternately on one side, and the corresponding IR receiving element and the transmitting side may be arranged on the other opposite side.

In any configuration, semi-outdoor or full-outdoor touch screens adopting IR touch technology should show the durability of IR touch screens that are released against solar interference conditions. As they have the largest interference power in addition to the IR transmission signals in the receiver. This should allow the system installer to think about additional ways to reduce touching errors.

*Full-outdoor environment: installation of ceiling guard to cover sunlight.

*Semi-outdoor environment: installation inside the glass window, etc.

 

As a result, we want to present new terms for these durability regulations:

  • Minimum Facing Angle (MFA) refers to the minimum angle of the line of sight (LOS) of the IR receiver. The smaller the angle, the greater the durability. This results in lowering the cost of installing systems in the field, meaning that the conditions are not tricky.
  • Sunlight Interference Power at MFA indicates the amount of sunlight interference that can withstand the maximum of MFA conditions. These two factors are in a trade-off relationship and have a more sensitive interfering relationship with MFA than Interference Power.

For example, a product with a durability of 30 degrees at 10,000 Lux can be compared to 32 degrees at 150,000 Lux or 28 degrees at 60,000 Lux. Measurement methods for these MFA and Interference Power are described in detail at www.itgocorp.com.

 

There are no companies that offer these two elements in the IR touch screens yet, but it is said that the MFA is about 30 degrees at 100,000 Lux. Unfortunately, the current companies have no measurement methods or regulations for these upcoming durability elements. Most of them are available in screen sizes of 30 inches or less. As the of touch screen increases, the above figures for the MFA and Sunlight Interference Power will get worse.

Assuming that the MFA 30 degree is installed without restrictions on the outdoor installation conditions (e.g., standalone installation, no shading, and the IR receiver is installed in line within the sun’s orbit), the receiver of the touch module will be exposed to sunlight in the daytime. If the sunlight reaches within 180 degrees, this would be considered as the whole angle of sunrise and sunset.

 

If the durability of the product is 30 degrees,

(30 degrees/180 degrees)*100(%)=16.6(%)

16.6 (%) * 12 hours would provide the number of touch errors that may occur for the duration of 2 hours.

 

If the solar interference level is reduced to 60,000 Lux (which is less than 100,000 Lux for 2 hours,) the time for the touch error is reduced, but the error probability would not decrease significantly.

(28 degrees/180 degrees)*100(%)=15.5(%)

15.5% * 12 hours = 1.87 hours does not indicate a significant decrease.

 

Also, the touch system is dependent to the location(s). It cannot be excluded when the angle between the IR touch receiver and the sunlight is within 30 degrees for more than 2 hours.

In conclusion, the specification of the IR touch screen should have a smaller MFA and a higher Interference Power in the prescribed MFA is better. This means that the better the durability of the product in terms of the system integrator as the installation cost is low and the installation site is independent.

The key to the success of the touch screen is that the installation location should be on the line where the customer is moving as far as possible. Therefore, the importance of the place of installation must be considered first as it must be easy and convenient to use.

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