User's Manual

LX-80 User Manual
Page 14 of 32
4.6. Relative measurement
Each sensor unit measures the distance between the sensor and the first detected
object. For water level measurement, it is preferred to report the actual water level from
the bottom of the riverbed to the surface of the water. That is why we offer relative
measurement, which is calculated relative to mounted sensor height. Sensor height is
defined as the distance from the mounted sensor position to the bottom of the riverbed.
This distance is a fixed value unique to every mounted unit. It can be set to the device in
two ways.
First is by setting the sensor height parameter directly using any of communication
protocols described in the following chapters. After setting the sensor height, relative
measurement will be calculated by the following formula:
    

  
  
  
For example, if the sensor is mounted 6.35m above the riverbed, and the measured
distance from sensor to the surface is 4.34m then the real water level is calculated as the
difference of these two values; 6.35m – 4.34m = 2.01m
In this case the sensor will report 4.34m as measured level and 2.01m as measured
relative level.
Alternatively, it is possible to set sensor height indirectly, using the staff gauge
measurement. In this case staff gauge measurement needs to be taken directly underneath
the position of the mounted sensor. When setting the sensor height using staff gauge
height, the following formula will be used to calculate sensor height:
    

  
  
  
For example, the sensor is mounted at an unknown height above the riverbed and
using staff gauge it is determined that the water level at that given time is 1.34m. The
sensor detects water at the distance of 6.02m. By setting the value 1.34m as staff gauge