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Analog Motion Sensors
Published in Clarence W. de Silva, Sensor Systems, 2016
A schematic diagram of an eddy current proximity sensor is shown in Figure 8.20a. Unlike variable-inductance proximity sensors, the target object of the eddy current sensor does not have to be made of a ferromagnetic material. A conducting target object is needed, but a thin film of conducting material, such as household aluminum foil glued to a nonconducting target object, would be adequate. The probe head has two identical coils that form two arms of an impedance bridge. The coil closer to the probe face is the active coil. The other coil is the compensating coil, which compensates for ambient changes, particularly thermal effects. The remaining two arms of the bridge consist of purely resistive elements (see Figure 8.20b). The bridge is excited by a radio frequency voltage supply. The frequency may range from 1 to 100 MHz. This signal is generated from a radio frequency converter (an oscillator) that is typically powered by a 20 V DC supply. When the target object (sensed object) is absent, the output of the impedance bridge is zero, which corresponds to the balanced condition. When the target object is moved close to the sensor, eddy currents are generated in the conducting medium because of the radio frequency magnetic flux from the active coil. The magnetic field of the eddy currents opposes the primary field, which generates these currents. Hence, the inductance of the active coil increases, creating an imbalance in the bridge. The resulting output from the bridge is an amplitude-modulated signal containing the radio frequency carrier. This signal is demodulated to remove the carrier. The resulting signal (modulating signal) measures transient displacement of the target object. Low-pass filtering is used to remove high-frequency leftover noise in the output signal once the carrier is removed.
Silicon Carbide Surface Quality Prediction Based on Artificial Intelligence Methods on Multi-sensor Fusion Detection Test Platform
Published in Machining Science and Technology, 2019
Yawei Zhang, Beizhi Li, Jianguo Yang, Xiao Liu, Jinqiang Zhou
Workpiece can be fixed with clamping ring and two lathe centers in the high precision multi-sensor detection modules, different sensors are mounted on the sensitive positions to measure signals, which include one force sensor, two accelerometer sensors, one acoustic emission senor and one electric eddy current sensor. A triaxle force sensor 9347C from Kilster Co. (Sindelfingen, Germany), is mounted on tailstock, which has the measurement range from –15 kN to 15 kN, and the sensibilities of measurement force FX, FY, FZ are –7.8 PC/N, –7.8 PC/N, –3.7 PC/N respectively, the directional natural frequencies of X, Y and Z are 3.6 kHz, 3.6 kHz, 10 kHz. The measurements of the force mean value and dynamical incremental with dynamic gauge of Kistle can be measured in the grinding experiments. Two accelerometer sensors have been separately mounted above and ahead the force sensor to capture the vibration in X and Y direction, which have been used to measure the vibration of grinding procession. The model D1010A of accelerometer from Yangzhou Electric Science and Technology Co., Yangzhou, China, can measure the maximum value of 500 m/s2, which has an operation frequency range from 0.5 Hz to 10 kHz. Current sensor eddy NCDT3010 from Micro-Epsilon Co., Ortenburg, Germany, has been placed with special fixture 0.5 mm away from workpiece , it is used to measure radical surface of workpiece in the grinding process. Workpiece runout can be measured with Electric Eddy current sensor too, and its accuracy can achieve 0.008 μm with good dynamic response performance. Its test principle is relevant to the electromagnet, and its measurement accuracy are not interfered by the surroundings. The signal acquisition card from LMS is put into use for ensuring the accuracy and anti-interference of measurement process in the data acquisition and analysis modules, and the acquired data are put into IPC to be processed and be analyzed.