Manufacturing Automation Systems
Automation System and Development
Since 2003
Phone 607-368-9097

Case Study: Process Control System

The Challenge:

A large Western NY Company required the ability to apply controlled microwave and radiant heating profiles on products made up of various chemical composition. There were several challenges that this application had to address: The Solution

To keep cost down, most of the hardware needed to generate the microwave energy was reused, only the control system was replaced to accommodate requested functionality.

The software developed by Manufacturing Automation Systems allows the user to create and run recipes (i.e. temperature profiles) on samples placed inside an oven. The temperatures can vary anywhere from 25⁰C to 1000⁰C, and the recipe allows the user to create a custom temperature profile to be applied on the sample. Data is then collected during the recipe duration, which can last for many hours.

The overall strategy in developing this application was to decouple the user interface, running on a Windows PC, from the temperature control, running on a National Instruments Real-Time controller (i.e. compactRIO). When the user is ready to run a sample, a recipe (previously created by the user) is automatically downloaded from the host computer to the real-time target. The real-time controller interprets the recipe, and begins to monitor the temperature, control the microwave and radiant source, monitor various safety interlocks, collect and stream data. Status information, along with the data, are bundled and transmitted back to the host computer, where the user is able to monitor test conditions. Because the recipe is running on a real-time system, the host computer can be disconnected without affecting the test or missing any safety interlocks. The screen shot below shows and example of the data displayed to the operator during the test.
The software developed for the real-time controller was architected to use several state machines with several independent loops running in parallel. For example, a safety loop monitored all interlocks during the test and immediately shutdown the system if an error condition arose (i.e. overheating, oven door open, etc.). A communication loop was responsible for receiving and transmitting data between the controller and the host computer.

The data transmitted back from the target to the host computer was directly streamed to a tab-delimited text file. This file can then be easily opened and analyzed in Excel, as shown below:
The system is configured to capture data every 100 msec from all the thermocouples, microwave forward and reflected power, and other sensors.

Another part of the application, exclusive to the host computer, provides the user with a recipe editor. The editor allows the user to create a new recipe or modify existing recipes. The user can insert various steps to create the temperature profile needed for a sample under test. The screen shot below show an example of several test step entries:
For each step in the profile, the user specifies various parameters, such as how the microwave is to apply power (i.e. step to power level, ramp to temperature, soak at temperature, etc.), or which control algorithm to use (open-loop, PID, PID with On-Off, etc.). One key objective that had to be met was the ability to shield the operator from entering specific PID values when using PID control. This was accomplished building a database collection of material compositions and their associated PID values. If an unknown material behaves similar to one of the known entries in the database, then those PID gain values are selected. This method tries to remove the tedious trail-and-error process of determining the optimal PID gain values for a material each time.
Some additional technical highlights:
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