Signal-conditioning devices:
In some literature, signal-conditioning devices such as electronic amplifiers are also classified as transducers. Since we are treating signal-conditioning and modification devices separately from measuring devices, this unified classification is avoided whenever possible, and the term transducer is used primarily in relation to measuring instruments.
Note that it is somewhat redundant to consider electrical-to electrical transducers as measuring devices, because electrical signals need conditioning only before they are used to carry out a useful task. In this sense, electrical-to-electrical transduction should be considered a “conditioning” function rather than a “measuring” function. Additional components, such as power supplies and surge protection units, are often needed in mechatronic systems, but they are only indirectly related to control
Functions.
Relays and other switching devices and modulators and demodulators may also be included. Pure transducers depend on non-dissipative coupling in the transduction stage.
Passive transducers (sometimes called self-generating transducers) depend on their power transfer characteristics for operation, and do not need an external power source. It follows that pure transducers are essentially passive devices. Some examples are electromagnetic, thermoelectric, radioactive, piezoelectric, and photovoltaic transducers. External power is required to operate active sensors/transducers, and they do not depend on power conversion characteristics for their operation.
A good example is a resistive transducer, such as a potentiometer, which depends on its power dissipation through a resistor to generate the output signal. Note that an active transducer requires a separate power source (power supply) for operation, whereas a passive transducer draws its power from a measured signal (measurand). Since passive transducers derive their energy almost entirely from the measurand, they generally tend to distort (or load) the measured signal to a greater extent than an active transducer would.
Precautions can be taken to reduce such loading effects. On the other hand, passive transducers are generally simple in design, more reliable, and less costly in the present classification of transducers, we are dealing with power in the immediate transducer stage associated with the measurand, not the power used in subsequent signal conditioning. For example, a piezoelectric charge generation is a passive process.
But, a charge amplifier, which uses an auxiliary power source, would be needed in order to condition the generated charge.
Next, we will study several analog sensor-transducer devices that are commonly used in mechatronic system instrumentation. We will not attempt to present an exhaustive discussion of all types of sensors; rather, we will consider a representative selection.
Such an approach is reasonable in view of the fact that even though the scientific principles behind various sensors may differ, many other aspects (e.g., performance parameters, signal conditioning, interfacing, and modeling procedures) can be common to a large extent.
