Abstract:
One of the difficult duties in chemical industrial units is the determination of
the level of liquid for real – time monitoring. Determination of this parameter
is useful in process control loop. Hence present study is devoted for this
purpose by employing microbend based optical fiber sensor.
In optical fibers the microbending is considered as a one of the unwanted
properties in optical communications due to its effect on attenuating and
distorting the transmitted signals. Nevertheless, it's possible to exploit this
property in modulating the light intensity and hence using the fiber as liquid
level sensor.
In this work, in order to continuously monitor liquid level in petroleum and
chemical industries, an optical fiber sensor based on microbend effect was
designed and manufactured. The system is consist of a sensor that is
composed of a microbend modulator, sensing fiber, emitting / detecting
devices, in addition to liquid container unit, and an electronic circuit was used
to control the liquid level.
Four threaded aluminum blocks with different spatial period, and one flat, are
used to generate microbending in a multimode step index fiber. These blocks
(one flat and another threaded for each case) cross the fiber and pressed by the
liquid container unit, liquid pressure is converted into small displacement of
portable block, and then the sensing fiber is bent and the through light
intensity is reduced. By detecting the output light power, liquid level can be
obtained according to the exerted pressure. A relation between the resulting
laser output in term of voltage and load in term of liquid height, and spatial
period (number of teeth) are obtained in each case. So the conclusion is that
the mechanism of microbending can be used in optical fiber to produce a
liquid level sensor, and then control of that level.
Using pressure measurement to determine liquid level is particularly useful
for applications with foaming or bubbling liquid, where other level
measurement technologies have difficulties.
The results show that the laser technique is both accurate and immediate.
Test results show that this sensor is suited for dangerous applications of liquid
level measurement especially in fields where electrical isolation and / or
electromagnetic interference (EMI) resistance are strictly required.
