In case AC power is supplied to electric instruments,
the power is supplied through transformer. One purpose of transformer
is to convert the power voltage to meet each instrument's power requirement
and to supply the power to it. Another purpose of this is the isolation.
Isolation between primary coil and secondary coil inside transformer
minimizes mutual influences.
As for AC signal, it is common to isolate between input signal and
output signal through input and output transformer. These transformers
provide not only impedance conversion but also circuit protection
and noise elimination against various troubles coming from signal
line.
As for DC signal, we can see many cases of non-isolation between transmitter
(field site) and control instrument (control site) because it is difficult
for us to find economical and reliable isolation method such as transformer.
If your system is simple and is installed in a good electric environment,
it is not necessary to install isolator units in your loops, however,
you will meet an electric problem in case one signal is distributed
to various instruments and your system is installed in noisy environment.
Under this condition, if some electric trouble happens, the trouble
may be spread out. By using isolator units, this kind of problem is
solved. |
Circuit Diagram of Isolator, Model M2VS |
|
What's
the isolator unit used for?
Isolator
is installed between a transmitter (i.e. sensor) and a receiver to galvanically
isolate DC signals. Since field instruments (at field site) and control
instruments (in control room) are isolated electrically through an isolator
unit, we can minimize various influences coming from field site to control
instruments (in control room).