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How to prevent unwanted measurement on fog with the Dx1000 distance sensor
Article No: KA-09320
Version: 1.0
Subject to change without notice
This article describes how the fog filter works with the Dx1000 distance sensor and when it should it be activated.
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Dx1000
Table of Contents
Depending on its density, fog can reflect the laser light emitted by the Dx1000 distance sensor and lead to an echo above the detection threshold in the distance range up to approximately 20 meters. If "first echo" is selected in the measurement settings, the distance of the fog may be erroneously output instead of the natural object (DT1000) or reflector (DL1000) located behind the fog.
This behavior can be prevented by two different measures:
1. Selecting "last echo" instead of "first echo":
This is the recommended setting if the last echo actually represents the echo of the desired measurement object. However, if a part of the light spot passes this measurement object and hits an object behind it that is located within the distance range and signal level range defined in "Echo selection", this workaround cannot be used. In this case, we recommend using the fog filter as described below.
2. Activation of the fog filter:
The Dx1000 has the fog filter activated as a factory default setting in the measurement settings.
This increases the minimum signal level (RSSI value), from which the echo of a measurement object at a distance of between 0.2 and 20 m is evaluated, from 500 digit to 1300 digits. As this value is above the typical signal level of fog, unwanted fog echoes can be suppressed. The fog filter has no effect on the evaluation of echoes from distances above 20 m.
The increase in the minimum signal level associated with the activation of the fog filter means that the first echo behind the fog is evaluated instead of the fog, as long as it has an RSSI value above the value specified in the table below.
Note:
The fog filter should only be activated if the application requires the first echo to be evaluated and fog is present in the first 20 m of the measuring section in a density that would result in undesired detection of the fog.
In all other cases, the fog filter should be deactivated. This prevents objects that provide a low signal level (RSSI < 1300) due to their optical properties from not being detected in the distance range up to 20 m and therefore "no echo" being output.
If necessary, the measurement cycle time can be increased for object distances > 20 m in order to detect the object even if the signal level is very low due to fog attenuation.
