Page 401 - Sensors and Control Systems in Manufacturing

Industrial Sensors and Contr ol
Problems to be solved for this sensor are dirt contamination on 355
the prism surface and bubbles in the liquid. Enclosing the sensing
element with a fine filter helps keep it clean and simultaneously
reduces level fluctuations caused by bubbles. Since optical-fiber liquid
level sensors have the advantages of low cost and electrical isolation,
their use is widespread in petroleum and chemical plants, where the
hazardous environment causes difficulties with conventional sen-
sors. They are used, for example, to monitor storage tanks in a petro-
leum plant.
Another optical-fiber liquid level sensor, developed for the mea-
surement of boiler-drum water levels, employs a triangularly
shaped gauge through which red and green light beams pass. The
beams are deflected as it fills with water so that the green light
passes through an aperture. In the absence of water, only red light
passes through. Optical fibers transmit red or green light from indi-
vidual gauges to a plant control room located up to 150 m from the
boiler drum (Fig. 7.35). The water level in the drum is displayed
digitally.
This liquid level sensor operates at temperatures up to 170°C and
pressures up to 3200 lb/in gauge. Many sensor units are installed in
2
the boiler drum, and most have been operating for seven years. This
sensor is maintenance-free, fail-safe, and highly reliable.

7.17 Sensory MEMS Enable Certain Molecules to Signal
Breast Cancer’s Spread
Metastasis is responsible for approximately 90 percent of all cancer-
related deaths. Sensory MEMS technology enabled researchers to
uncover how breast tumors use a particular type of molecule to pro-
mote metastasis. It also revealed that tumor cells learn to exploit cyto-
kines to promote the spread of breast cancer.
The work of several scientists examine how cells in the body com-
municate with each other through cytokines, signaling molecules
that direct a wide range of activities such as cell growth and move-
ment. One important cytokine transforming growth factor (TGF) nor-
mally suppresses tumor development. However, according to the
findings, cancer cells in humans are able to misuse these cytokines for
their own gain by compelling TGF to enhance a tumor’s ability to
spread instead of suppressing it.
Using computer-based analysis to classify patient tumor samples
based on their levels of TGF, it was observed that about half of all
breast tumors contained active TGF. The affected tumors were found
to be more aggressive and more likely to metastasize to the lung dur-
ing the course of the patients’ disease.