An arrangement for measuring the true position of a diaphragm within a diaphragm
valve assembly utilizes an optical probe in conjunction with a reflective surface
formed on the backside of the diaphragm membrane. An optical test signal is launched
from a source (such as an LED or laser) along a waveguide (such as an optical fiber)
so as to impinge upon the reflective surface of the membrane. The reflected test
signal is then coupled back into the waveguide and directed toward an optical receiving
device. The received optical signal is translated into an electrical signal that
is used as an indication of the "state" of the diaphragm. That is, as the diaphragm
membrane moves between the "open" and "closed" position, the membrane surface will
be deformed and thus modify the amount of reflected optical signal that is directed
back into the probe. Therefore, the true position of the diaphragm can be determined
by monitoring the generated electrical signal from the optical probe. Position
values between the "open" and "closed" positions can also be determined, as well
as the fluid pressure on the process side of the diaphragm.
