How a Photoswitch Saved My Job
(by Larry Bush)
In 1996 I was employed as maintenance supervisor at an olive cannery in
the heart of California's fertile San Joaquin valley. We were restarting
the cannery after an extended shutdown while the cannery changed owners.
This was my first opportunity to work in the food industry and a
cannery. There were issues for me to learn and learn fast. The new
harvest season's olives were due to start arriving just four weeks after I
Only four of the previous maintenance personnel were available to be
rehired, so things were looking a little bleak at times. None of the new
mechanics or electricians had food industry experience, either. In
addition, there were almost no blueprints or wiring diagrams for the
entire cannery or processing plant.
However, on the scheduled startup day, everything ran. Our two main
lines used Angelus 60L Seamers with a maximum output capability of
600 cans per minute. That figures out to ten cans per second. That's
faster than I can count. The Seamers seal the end cap onto the cans. Due
to space limitations, new, spiral elevators had been designed and added by
the previous owners. The elevators and controls had been wired up but they
never ran prior to shutdown.
We started up slow, but problems immediately surfaced. The discharge
line from the spiral elevator to the cooker was a plastic cable line. Cans
could tip over and jam. When the can jam-up backed cans into the discharge
from the spiral elevator and then round and round the elevator. It took a
considerable effort and time to remove the jammed cans from the elevator.
A photoelectric sensor with a reflective lens was installed on
the discharge cable line about six inches from the can entry to the
discharge cable line. This sensor was designed and connected to stop the
seamer and elevator when a jam-up occurred. The sensor had to see an
opening between the cans, operate on/off, or it would shut down the
It turned out that the photoelectric sensor could only be adjusted to
stay on all the time or off all the time when the cans were going by at
any higher rate than Jog speed on the Seamer. We adjusted and adjusted the
sensors. The sensors were replaced with new sensors. It did no good. The
lines were stopped while we traced all the control and power wiring so we
could try to determine if there was a problem in the wiring.
When I looked around, the Plant Manager, accompanied by the company
President, Vice President and the Financial Controller were standing to
the side watching me. All four of them had their arms crossed and
unreadable expressions on their faces. I knew I was in trouble and had to
get on top of this problem in a hurry.
Finally, I determined that the previous engineer had ordered an
incorrect application for the original photoelectric sensors. I looked up
the specifications for the installed sensors and found that their response
time was not fast enough to "see" the cans as they went by. I
looked in an Allen-Bradley sensor book for a photoelectric sensor with a
fast response time, able to withstand the harsh environment of a
cannery (steam and water), and would continue operation even when
subjected to lots of vibration.
The photoelectric sensor I decided on was the Allen-Bradley Series
4000B Bulletin 42RL. This sensor has a response time of 5
milliseconds. That time was faster than our requirements. The case of the
sensor is designed for harsh environments and kept the steam and wash-down
water from entering the delicate, control circuitry area of the sensor.
The vibrations from the elevator and the cable line had no effect on the
solid state wiring of the sensor.
After installation, the sensor was connected and pre-adjusted for the
can stream. The sensor kept the cable line and elevator running and was
"seeing" the individual cans. We physically simulated a jam-up
of cans on the cable line. When the cans backed up to the sensor, the
sensor operated and shut down the spiral elevator and opened the
clutch on the seamer, stopping line production.
There remained only some fine tuning of the sensor as we ramped up to
top speed of between 550 and 570 cans per minute. Again, we had a
"command" audience of the top company officers for our startup.
When the lines started and continued running or stopped on a can backup
with no corresponding elevator jam, there were smiles all around. My
job was safe.
Most of the can jams on the cable line were reduced to acceptable
levels by the work of the Cookroom Manager and his Seamer
Operators/Mechanics. They reworked the can drops and built-in several can
cutouts. The can cutouts are places where a can lying on its side will be
ejected from the cable line, thereby eliminating an almost certain jam in
a can drop or at the Cooker entrance. By reworking the can drops, can jams
in the drops were almost totally eliminated.
Besides the fact that I kept my job, I learned that anyone can make a
mistake and, when in doubt, check the factory specifications of the
equipment you are working with.
Be sure and download Larry's New Book ...
Policy and Procedures Manual Ebook"
management has a direct quantitative and qualitative effect on the
productive output of the business entity."
Also watch for more articles by Larry Bush at www.feedforward.com.au/articles-technical-writings.htm
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