Piezoelectric Sensors and Strain Gage Sensors
Two working principles have become dominant in the measurement of forces: Piezoelectric Sensors and Strain Gage Sensors.
The sensors with piezoelectric technology are active measurement systems ; they do not require an external energy. They consist of two discs of crystals with an interposed sheet electrode. When you apply the force you generate an electrical charge measured by a charge amplifier. The charge is proportional to the force applied. Due to their principle of operation, the piezoelectric sensors have a drift estimated 1 N / minute while the measurement chain is in operation. Since this value remains unchanged regardless of the measured force, the measurement error resulting from the relative drift is particularly unfavorable when measuring forces for long periods of time.
The piezoelectric sensors show very small deflections when the force is applied because they offer high rigidity. Consequently, a high resonance frequency which, in principle, is very favorable to the quasi-static or dynamic applications. The piezoelectric sensors can be very compact and they are therefore the optimal solution when it is required the integration in existing systems. In conclusion, we can say that the piezoelectric sensors are the first choice for fast measurement of small forces.
The force transducers based on strain gage are passive measurement systems; so they require an external energy. They always include an elastic element to which force is applied. This force causes a slight deformation of the elastic element. They are connected together at least four strain gauges forming a Wheatstone bridge circuit. Feeding the measuring bridge with a voltage, the resulting output voltage is proportional to the force applied. These sensors do not show almost no drift and are therefore particularly suited to the tasks of monitoring long-term static such as weighing. he so-called sliding (reversible variation of the output signal dependent on the time that appears by applying a constant force), is extremely small, since it can be minimized by the appropriate choice of the conformation of the gage.