Posts Tagged ‘programmable logic controller’

The Depositor’s Industrial Control System

Friday, August 24th, 2018

    Last time we saw how a solenoid valve operates a pneumatic actuator in a jelly depositor in a food manufacturing plant.   The operation was manual.   In other words, an electrical switch had to be thrown by hand each time to get the solenoid to work.   This can be rather tedious, when you consider the thousands of pastries that must be filled on each production run.   Now, let’s see how the solenoid can be automatically turned on and off by an industrial control system.

    In food manufacturing plants, industrial control systems are typically made up of programmable logic controllers, otherwise known as “PLCs.”   The PLC is an industrial computer that is used to control equipment like conveyor belts, motors, pumps, robots, and solenoid valves.   The PLC is connected to Input/Output Modules, or “I/O Modules.”

    The I/O modules act as an interface between the computer and the equipment in the plant.   As such, they contain a means to connect electrically to the computer and the plant equipment.   In the case of our solenoid valve, the PLC computer program would turn the valve’s solenoid on and off.   Whether it is turned on or off depends on the computer program’s timing and/or external sensors and how it feeds in conveyor belt/pastry position data to the PLC.    The result is the automatic depositing of jelly filling as each pastry passes by the depositor nozzle.

The Depositor’s Industrial Control System

The Depositor’s Industrial Control System


    That wraps things up for our blog series on depositors.   Next time we’ll move on to a new topic.

Copyright 2018 – Philip J. O’Keefe, PE

Engineering Expert Witness Blog



Food Manufacturing Challenges – HACCP Design Principle No. 3

Sunday, October 30th, 2011
     How do parents make life safer and healthier for their kids?  One of the ways is to  impose limits on things like roaming distance within the neighborhood, curfews, and insisting that you eat your vegetables.  Just common sense, right?  Let’s take a look at some more of it.

     Limits are also necessary within the food manufacturing industry.  Let’s take a look at Hazard Analysis and Critical Control Point (HACCP) Principle No. 3 to see how they’re established and why.

     Principle 3: Establish critical limits for each critical control point. – You can think of a critical limit as a boundary of safety for each critical control point (CCP).  So how do you determine that boundary of safety?  It’s difficult to generalize, but if you’ve ever watched the TV show Hoarders, you have an excellent example of one that has not only been breeched, but torn asunder.   

     In order to prevent things in the commercial food industry from getting anywhere near Hoarders bad, maximum and minimum values are set in place, representing safeguards to physical, biological, and chemical parameters at play within the industry.  Critical limits can be obtained from regulatory standards and guidelines, scientific literature, experimental studies, as well as information provided by consultants.  These critical limits come into play with issues as varied as machine design, raw material temperatures, and overall safe processing times.

     How could the hoarders let things get so bad?  If you listen carefully, you’ll hear bits of information that provide a clue.  They’ll say it started with a few things falling to the floor which they didn’t feel like picking up and it escalated from there. 

     Now all of us live within environments which differ as to their cleanliness, but by and large we live within space where we feel comfortable and consider to be reasonably clean.  We don’t all habitually move stoves and refrigerators to clean, for example.  But if we were so inclined, refrigerators do come with front access panels that are easily removed.  Trouble is the space they provide access to often isn’t large enough to accommodate hands and a vacuum cleaner nozzle comfortably.  You can imagine how frustrating and potentially dangerous it would be to public health to have commercial machinery that provided such limited access for cleaning.    

     To cope with this problem design engineers institute minimum and maximum parameters, such as in the critical limit dimensions of a removable cover.  Their guideline would ensure that enough space is provided so that personnel can fully access all aspects of machinery with tools for cleaning.  That same cover can also have established maximum critical limits, so that dimensions aren’t too large and heavy to be manipulated by hand.  Human nature being what it is, something that is too difficult to remove may be “forgotten” and parts of the machine may never get cleaned.

     Raw meats and many produce can contain hazards like salmonella, E. coli, and other nasty critters that are dangerous to human health.  One of the ways the commercial food industry works to ensure that these contaminants aren’t unleashed on the public is to install programmable control systems into processing machinery that essentially cooks the meat at an established minimum temperature for a minimum amount of time.  Utilizing this type of temperature control in conjunction with an established maximum cooking parameter for temperature and time will virtually eliminate the possibility of overcooked or burnt food products.  When you buy that frozen dinner in most cases it’s completely cooked, but it’s a rarity to find it’s been burned.  

     Another situation in which critical limits are utilized is in the maintenance of machinery, such as when they limit the number of hours a machine can be operated before it is shut down for servicing.

     Next week we’ll move on to Principle No. 4 and see how it establishes monitoring requirements for each CCP.  ____________________________________________