Crc Press Mechatronics Handbook 2002 By Laxxuss Episode 2 Part 6 pdf

Worst-case range measurement accuracy is ±5 cm, with typical values of around ±2 cm. The pulsed near- infrared 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. 19.68). The sensors are rugged since they have no moving parts. They can be operated safely in explosive environ- ments, 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 10.56 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 10.525 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 × 5 MHz/0.001 s). In this case, 0.0256 mm (0.001 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. Phase Measurement Time-of-flight (TOF) is defined as a phase shift between emitted and received signals when the dis- tance is less than one wavelength (Fig. 19.69). Given a phase shift f , the distance is calculated as FIGURE 19.68 The microwave sensor, unlike the motion detector, requires a separate transmitter and receiver (adapted from Williams, 1989). FIGURE 19.69 Range from phase measurement. Phase Locked Loop Output Receiver Transmitter Filter Preamp Modulator 0 1 2 3 4 5 6 7 8 012 345 Time Amplitude Emitted Signal Return Signal Phase 0066_frame_C19 Page 94 Wednesday, January 9, 2002 5:32 PM ©2002 CRC Press LLC Worst-case range measurement accuracy is ±5 cm, with typical values of around ±2 cm. The pulsed near- infrared 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. 19.68). The sensors are rugged since they have no moving parts. They can be operated safely in explosive environ- ments, 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 10.56 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 10.525 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 × 5 MHz/0.001 s). In this case, 0.0256 mm (0.001 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. Phase Measurement Time-of-flight (TOF) is defined as a phase shift between emitted and received signals when the dis- tance is less than one wavelength (Fig. 19.69). Given a phase shift f , the distance is calculated as FIGURE 19.68 The microwave sensor, unlike the motion detector, requires a separate transmitter and receiver (adapted from Williams, 1989). FIGURE 19.69 Range from phase measurement. Phase Locked Loop Output Receiver Transmitter Filter Preamp Modulator 0 1 2 3 4 5 6 7 8 012 345 Time Amplitude Emitted Signal Return Signal Phase 0066_frame_C19 Page 94 Wednesday, January 9, 2002 5:32 PM ©2002 CRC Press LLC . 0 066 _frame_C19 Page 94 Wednesday, January 9, 20 02 5: 32 PM 20 02 CRC Press LLC Worst-case range measurement accuracy is ±5 cm, with typical values of around 2 cm. The pulsed near- infrared laser is. 345 Time Amplitude Emitted Signal Return Signal Phase 0 066 _frame_C19 Page 94 Wednesday, January 9, 20 02 5: 32 PM 20 02 CRC Press LLC . 19 .69 Range from phase measurement. Phase Locked Loop Output Receiver Transmitter Filter Preamp Modulator 0 1 2 3 4 5 6 7 8 0 12 345 Time Amplitude Emitted Signal Return Signal Phase 0 066 _frame_C19