## 3 Development of Wireless Laser Displacement Monitoring Equipment
### The Principle of Laser Ranging Measurement
#### 3.1.2 Pulsed Laser Ranging  
Pulsed ranging is a measurement method that was first used in the field of surveying and mapping by laser technology. Due to the small laser divergence angle, the short duration of the laser pulse, and the maximum instantaneous power of more than megawatts, pulsed laser ranging has good directionality and a strong anti-interference ability. In ranging with cooperative targets, extremely long-distance measurements can be carried out, and when short-range measurements are carried out, cooperative targets are not needed and the target to be measured can also be measured by receiving the light signal of diffuse reflection. Pulse laser ranging has the characteristics of a simple system with long range, and a single measurement time that is faster than continuous laser ranging, but it also has the disadvantage of low single measurement accuracy [25].  
The pulsed laser emitted by the laser is reflected after hitting the target to be measured, and the reflected light is received and amplified by the photodetector of the ranging system. Taking the transmitted optical pulse signal as the timing start time and the received optical pulse signal as the timing end time and by measuring the time between the two, the time required for the laser to travel back and forth between the ranging system and the target can be obtained. The distance to the target to be measured can be converted from the general formula of distance measurement (\(\mathbb{S}=\frac{\Phi}{2}\)) by using the TOF method.  
The pulsed laser ranging system is usually composed of several modules: the control module, laser emission module, laser connection module, receiving module, time identification module, and time interval measurement module. Figure 2 is a schematic diagram of the pulsed laser ranging system.  
Figure 3 is the waveform and timing diagram of the pulsed laser ranging system, where the rising edge of the signal is discriminated. The round-trip time can be detected from the number of pulses digitally measured from the recording of the time between the reference signal and the echo signal.  
In the timing diagram of the pulsed laser ranging system, it can be clearly seen that the working process of the system is as follows: the pulsed laser emits laser pulses, and the laser pulses are used as emission signals. The signal reflects a small amount of energy to the receiving system as a reference signal through a half mirror and a half mirror, and most of the energy is emitted to the target through the half mirrors. The reflected light signal is received by the receiving system as an echo signal, and both the reference signal and the  
Figure 2: Schematic diagram of the pulsed laser ranging system.  
echo signal are received by the photodetector and converted into electrical signals. The obtained electrical signal is shaped and amplified, the reference signal is shaped as a start signal, and the echo signal is shaped as a stop signal. The two signals are discriminated to obtain the start and end time information, and this is the time when the laser is in the ranging system. The flight time between the targets is then monitored by the time measurement method to obtain the required data.