Distance Sensor (BGS/TOF) Technical Guide
Distance Sensor (BGS/TOF) measure the distance by measuring time difference from emitting light to receiving the light reflected at object surface. There are two major method to measure the time difference as follows.
1. Phase difference measurement method
The laser diode emits AM modulated laser beam and receiver gets the light reflected by target object. The sensor measures the time difference between emitted light and received light comparing the phase of those light and define the distance of the target object.
2. Pulse time difference measurement method
The laser diode emits pulses and the receiver gets them reflected at the target object. The sensor measure the time difference between those pulses by built-in timer and define the distance of the target object.
The measurement sensor measures distance and define a value of it. The value increases as the distance gets longer though, the value increases like step even if the distance changes linearly. The resolution of the measurement sensor is the minimum unit of the step.
4. Statistical error and normal distribution
Measurement result would distributes as right hand chart with a center value as mean of those values which is not always real center of the distribution. In statistics, the standard deviation (SD, also represented by the Greek letter sigma σ) is a measure that is used to quantify the amount of variation or dispersion of a set of data values. When it is normal distribution, 68.26% of all the data will be in +/- 1σ.
5. Accuracy and Repeat accuracy
6. Temperature drift
The deviation of measurement result which is made by temperature change.
Example: +/- 1%F.S./℃ (F.S. is Full Scale means measurement range)
7. Influence to measurement result by ambient temperature
The light speed is influenced 1ppm/K by the ambient temperature. The measurement result of TOF sensor is also influenced in the same way because it measures the distance by measuring time difference between emitting to receiving of the light. It means one millionth of the value changes by 1℃ change of ambient temperature.
8. Influence to measurement result by atmospheric pressure
The light speed is influenced 0.3ppm/hPa by the atmospheric pressure. The measurement result of TOF sensor is also influenced in the same way because it measures the distance by measuring time difference between emitting to receiving of the light. It means 0.3 millionth of the value changes by 1hPa change of atmospheric pressure.