Signal conditioning is the modification of a signal to make it more useful to a system. Two important types of signal conditioning are, of course, the conversion between analog and digital.
The rate at which data samples are taken obviously affects the speed at which the mechatronic system can detect a change in situation. There are several things to consider, however.
For example, the response of a sensor may be limited in time or range. There is also the time required to convert the signal into a form usable by the microprocessor, the A to D conversion time. A third is the frequency of the signal being sampled. For voice digitalization, there is a very well-known sampling rate of 8000 samples per second. If the ADC and DAC are on the same board as the microprocessor, they will often share a common clock. The microprocessor clock, however, may be too fast for the ADC and DAC. In this case, a prescaler is used to divide the clock frequency to a level usable by the ADC and DAC.
Filtering is the attenuation (lessening) of certain frequencies from a signal. This process can remove noise from a signal and condition the line for better data transmission.
Filters can be divided into analog and digital types, the analog filters being further divided into passive and active types. Analog passive filters use resistors, capacitors, and inductors. Analog active filters typically use operational amplifiers with resistors and capacitors.
Digital filters may be implemented with software and or hardware. The software component gives digital filters the feature of being easier to change.
Filters may also be differentiated by the type of frequencies they affect.
1. Low-pass filters allow lower set of frequencies to pass through, while high frequencies are attenuated.
2. High-pass filters, the opposite of low-pass, filter a lower frequency band while allowing higher frequencies to pass.
3. Band-pass filters allow a particular range of frequencies to pass; all others are attenuated.
4. Band-stop filters stop a particular range of frequencies while all others are allowed to pass.
Data Acquisition Boards
There is a special type of board that plugs into a slot in a desktop personal computer that can be used for many of the tasks above. It is called a data acquisition board, or DAQ board.
This type of board can generate analog input and multiplex multiple input signals onto a single bus for transmission to the PC. It can also come with signal conditioning hardware/software and an ADC.
Some units have direct memory access (DMA), where the device writes the data directly into computer memory without using the microprocessor.
While desktop PCs are not usually considered as part of a mechatronic system, the DAQ board can be very useful for instrumentation.