Amplifiers force sensors

The micro-force sensor, attached at the end of the IPMC-PVDF beam, has a similar structure as the IPMC-PVDF composite beam shown in Fig. 8.16, except that the IPMC layer is replaced by a (relatively) rigid passive film. In the prototype, we used 200 pm thick polyester film as the middle layer. The same charge amplifier circuit as in Fig. 8.17, with possibly different gains, is used for the force sensor. Analogous to the case of measuring the bending displacement, one can derive the sensitivity of the force sensor in terms of the electromechanical properties and dimensions of the layers [Chen et al. (2008)]. 

The experimental setup for measuring eleetromechanical performance of an IPMC actuator consists of a clamp to mount the IPMC sample, a data recording device (e.g., digital oscilloscope or computer equipped for data acquisition), a function generator, a current amplifier, a force sensor, and a laser displacement sensor or a video camera (Figs. 4 and 5). The process diagram of electromechanical characterization is given in Fig. 6. 

To monitor and control a tablet press, certain sensors must be installed at specific locations on the machine. These sensors are called transducers. In general, a transducer is a device that converts energy from one form to another (e.g., force to voltage). Tablet press transducers typically measure applied force, turret speed, or punch position. Because the signals coming from such transducers are normally in millivolts, they need to be amplified and then converted to digital form in order to be processed by a data acquisition system. 

In the ideal architecture all forces applied to the g-cell will be amplified the same regardless of their frequency. Therefore the gain would be distributed so that the input to the bandpass filter is the same as the output of the sensor. What occurs when the g-cell is subjected to a force greater than the output will follow (i.e., a 400 g shock with a 40 g output range) and the input is at a frequency less that the bandpass filter (400 Hz) is considered an in-band overload. The representative waveform is shown in Fig. 7.1.6. 

High sensitivity, selectivity, and ability to operate in turbid solutions are advantages of electrochemical biosensors. Amperometric detection is based on measuring the oxidation or reduction of an electroactive compound at a working electrode (sensor). A potentiostat is used to apply a constant potential to the working electrode with respect to a second electrode (reference electrode). A potentiostat is a simple electronic circuit that can be constructed using a battery, two operational amplifiers, and several resistors. The applied potential is an electrochemical driving force that causes the oxidation or reduction reaction. 

Progress in the development of SAW vapor sensor devices will proceed in several directions. Attempts to reduce SAW sensor noise will increase the emphasis on the use of SAW resonators and more sophisticated RF amplifier designs. Improved pac)caging schemes will be explored to reduce SAW temperature drift. Much of the temperature drift exhibited by dual SAW sensors is caused by unsymmetrical stresses imposed on the SAW devices as a result of thermal expansion of the pac)cage. Miniature temperature controllers for the SAW device may offer a brute-force fix for this problem. 

Often it is desirable to control the time constant, independent of sensor, cable, and input capacitances. In such a case it is recommended to use a charge amplifier (Fig. 4). The current delivered by the piezoelectric element is directly transferred to the capacitor Cm and the resistor Rm, irrespective of the sensor and cable capacitances Cp-and Cc- Under these conditions, the time constant is easily adjusted to allow for low-frequency measurements, where the sensor signal now follows the time-dependent force dF(t)/CM-... 

Fig. 7 Force measurement with a ferroelectret sensor coupled to a charge amplifier top). A rectangular varying compressive force is applied to the sample. Force rate measurement, when the ferroelectret sensor is connected to a digital oscilloscope bottom). Measurement signals can be calibrated to determine the piezoelectric coefficient of the ferroelectret foam sensor...

Toyota s electronically modulated suspension (TEMS) uses piezoelectric sensors and actuators in a vibration cancellation role (Fig. 3.46). The system senses the road vibrations with a five-layer piezoelectric sensor. When rough roads or hard turns are encountered, the sensor is stressed and outputs an electronic signal. The signal is amplified by a control unit, which outputs a voltage to the 88-layer piezoelectric actuator. The actuator expands up to 50 /im on a hydraulic motion amphfier, which expands to 2 mm. This displacement stiffens the damping force of the shock absorbers, all within a 20-ms period. 

Gautschi, G., 2002. Piezoelectric Sensorics Force, Strain, Pressure, Acceleration and Acoustic Emission Sensors Materials and Amplifiers. Springer, New York. 

This consists of a controller, load cell, amplifier, and oscilloscope. The controller manages the movement of the load cell with specific frequency and force. The force on the sensor surface is detected by the load cell when the load cell hits the sensor, and the electrical signals from the pressure sensor are enhanced by an amplifier and then collected and recorded by an oscilloscope. 

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