Planning for “Abnormal Exits”

One of the more obvious causes of abnormal exits is the proverbial power failure.  With a power failure, the programming logic has no vote in how the system handles itself.  When a power failure happens, the system behavior is dependent on the failsafe strategy of the mechanical designer.  The failsafe strategy is not usually as critical in machine control as it is in process control. When recovering from a power failure it’s important to know whether you had a graceful shutdown which can be accomplished by setting flags within the program to keep track of whether or not you were running and what you were doing.  Then based on what you were doing when the power failure occurred, you need to determine how to recover (if possible) from that interrupted condition. For example, you might have been scaling up an expensive batch of raw ingredients and were only part way through the batch.  If you have kept track of what you were doing and if in a sequence what step you were in and if batching what your previous actual weights were for the respective …

What About Speed?

The intent of this article is to bring awareness to the matter of speed and how it can be addressed early in a project rather than being surprised somewhere during development or worse yet commissioning. Have you ever been bitten by speed in delivering an automation project?  How do you determine whether speed is going to be an issue in an automation project?  What do you look at to determine speed constraints? I would venture a guess that most, if not nearly all, of those reading this blog will have been challenged by some speed constraint in their past projects.  In my own history I have had more than one occasion where I have had a “collision” with speed. So where might you expect speed to be a problem? I always look at packaging lines with a cautious eye.  Communication interfaces can have an impact on batch execution or order downloads or usage uploads or data collection, etc. Servos, vision systems, batching systems, machine control can all have their speed challenges. There may be elements in any packaging line that challenge the limits of classic …

Programming Methodologies and Total Cost of Ownership

If you have ever been involved with or had to fund a new application or an upgrade to an existing application and experienced excruciating pain (cost, duration, delays, …) in the process, then you might be interested in this. Carpenters have a saying – “Measure twice, cut once”.  It’s not quite the same, but planning out how the system should operate and perhaps as importantly what you want to prevent it from doing and even more important how to recover from an “abnormal exit” is ‘required thinking’.  Just for clarification, I am calling an abnormal exit some sort of ungraceful and unplanned stoppage for the system.  That could be a power outage or perhaps a drive failure or a chain breakage or an E-STOP or ……………. Just as you eat an elephant one bite at a time, you also have to tackle a large solution one sub-system at a time. I need to point out that this is not a treatise on “modular programming” in its purest form which is defined as “a software design technique that emphasizes separating the functionality of a program into independent interchangeable modules, such …

Batching Best Practices

This intent of this paper is to present a few Best Practices I have discovered over the years that lead to an improved performance of ingredient automation (batching) systems. Any welding should be done prior to installation of the load cells. Proper drainage should be provided to prevent the load point assembly from standing in water. All load cells must be on the same plane (level) within 0.5 degrees of each other (which is approximately an inch over 10 feet). In any batching application, the volume of material in transit between the shutoff device and the actual batch container has an impact on the ability to perform fine batch adjustments. Piping best practices are also important. Some liquid flow sensors require staying flooded in order to provide a reliable feedback signal. Nearly all flow devices need to be isolated from vibration and many flow devices (liquid and gas) assume a uniform velocity profile for their approach and exit. Even though today instruments are more tolerant of poor location, it is still best to locate the instruments with some consideration of the approach and exit conditions. …