Any project requires a plan. Any plan requires an understanding of everything
involved. The key to good signal conditioning is, to understand what is the big picture. What is the signal source? What is the nature of the measurement of the source signal? What is the receiver signal required? What distances are involved? The list goes on.
When you determine the type of signal and range of variation of the source, you need to compare that to the type of signal and range of variation required by the receiver. In some applications, the conversion directly between the two signals may not be the best solution. An example of this conversion being less than perfect is, one where the signal needs to be transported over a distance.
One of the problems with sending an instrumentation signal over long cables, is voltage loss due to resistance of the connection; if the signal is voltage based. In an application where a resistance needs to be converted to voltage, with the requirement that the connection be run with a long cable; it would be more appropriate to consider the use of a 2 step process, in the conditioning of the signal.
A signal that is better suited for long distances, is a current loop. 4-20mA current loops can allow a signal to be transmitted miles without loss. If the signal receiver is a voltage measurement device, a very simple method can be used to convert from current to voltage. The method is to terminate the loop with a shunt resistor. The shunt resistor is sized using Ohms Law (R=E/I), for a value that produces maximum
measurable receiver voltage at maximum transmitter current. The combination of the two steps creates the end result of, resistance to voltage conversion. For the
most part, current loop transmitters are a more flexible way to go. While they can be used for long distance transmission, they are not limited to it. As close as inches is just as suitable.
The ROI-XMA
is an improved way to read sensors. Multiple sensor types. Multiple signal
ranges. High linearity. High precision. Fast response. Long transmission
distances. True analog signal conditioning, not microprocessor based A-D
conversion.
