Tham khảo tài liệu 'crc press mechatronics handbook 2002 by laxxuss episode 2 part 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | FIGURE The microwave sensor unlike the motion detector requires a separate transmitter and receiver adapted from Williams 1989 . FIGURE Range from phase measurement. Worst-case range measurement accuracy is 5 cm with typical values of around 2 cm. The pulsed nearinfrared laser is Class-1 eye-safe under all operating conditions. Microwave Range Sensors Microwave technology may be used to measure motion velocity range and direction of motion Fig. . The sensors are rugged since they have no moving parts. They can be operated safely in explosive environments because the level of energy used is very low no risk for sparks . Their operating temperatures range from -55 C to 125 C. They can work in environments with dust smoke poisonous gases and radioactivity assuming the components are hardened for radiation . Typically microwave sensors are used to measure ranges from 25 to 45 000 mm but longer ranges are possible depending on power and object size. The reflected power returning to the receiver decreases as the fourth power of the distance to the object. Typical wavelength used ranges from 1 to 1000 mm. Time-of-flight is in the order 2 ns per foot of range reach the target and return . This translates into ms per mile of range. Measuring short ranges may pose a problem. For 1 in. resolution the circuit must resolve 167 ps. An alternate method more suitable to measure short distances is based on a frequency sweep of the signal generator. In this case the return signal remains at the initial frequency usually GHz and it is compared with the current frequency changed by a sweep rate. For example to measure a range of 3 ft one may sweep at 5 MHz ms. After 6 ns the frequency changes by 30 Hz 6 ns X 5 MHz s . In this case mm in. may be resolved easily. When using this method a signal amplifier that increases gain with frequency is necessary. See section Frequency Modulation for more details on frequency modulation methods. .
