April 26, 2012
Are you down with OPC...Provider?
In his last blog, "Old McDonald had a Farm," my co-worker Britt Reid did a great job describing our package of tools called DMS/DCS which allows you to collect data from many different sources. Today I am going to focus on one of the biggest "animals" on Old McDonald’s farm, the OPC Provider. OPC stands for Open Process Control and connects to the OPC server to assemble and publish data to the DMS DataStore or a Historian Table. The data being published could be coming in from Programmable Logic Controllers (PLCs), which are widely used in the manufacturing world, predominately for motion control and process control. Now I can see your scratching your head and thinking "what does this has to do with SPC?" Well, I can tell you that using an OPC Provider could potentially help you find some precious treasure: Sources of Variation. Let me explain with an example.
I’m sure you have heard about how difficult it is to make chocolate soufflé. Not only do you have to worry about the quality of the ingredients that you use (raw materials) or the speed that you mix them, but you also have to make sure the oven is at just the right temperature. If the temperature of the oven is too high, the soufflé may burn on the outside without cooking in the center; on the other hand, having the temperature too low, means that the soufflé won’t rise properly. Now if you entered your soufflé in a contest, the judges would likely evaluate the quality of the soufflé based on taste, texture, and height. As described above, the majority of these quality characteristics depend on the conditions in which that soufflé was made in. In the manufacturing world, those conditions are called process parameters. As you can see, your process parameters could have a great influence in the final result of what you are making and the product characteristics that you are trying to control.
Sometimes we stand on a production line and get values that are out of control or out of specification and it is hard to figure out what the source, or sources, of the problems might be. This is when we start tampering with the process because we feel like we need to do something as our frustation level gets higher and higher. Many times, tampering the process can actually worsen the situation.
Recording and controlling the values that come from our process parametes can help us identify and respond to the correct source of variation. By doing some analysis we have the potential to find a correlation between some of the process and product parameters. Therefore, having our process parameters in control is just as important as having our product parameters in control. To see this, we can put our control charts in "engineering mode" to allow us to view more than one chart at a time in a single glance (see chart below). In this example, we see that when the temperature of our oven went out of control, so did the height of the souffles.
The OPC Provider Configuration:
The OPC configuration is actually very simple since most of the work has to be done upfront with the OPC Server. In ProFicient, we have to select the OPC Server that we want to connect to and then select all the variables that we are interested in monitoring. These variables represent OPC items and they will show up automatically after we select the corresponding OPC Server. In the example below, we were interested in tracking data coming in from three OPC items. Now, I recommend naming the OPC items in a way that easily helps you identify the type of data the OPC items are pulling from.
All of this is done in the DMS and then we use the DCS to assign the frequency in which we want to collect the data. We can also associate the data coming from the OPC Server with data from all other systems like a Database or a Gage.
We can actually get very creative in the way that we use our OPC Provider. We can even go a step further than recording product and process parameters and have our OPC Server send us information related to the status of our lines; like downtime, for example. For more information on this topic, refer to Chris Kearsley’s blog, "Quality System Integration-Closing the loop with OPC." InfinityQS is able to communicate back to our OPC Server and send commands that allow us to automatically react to the issue.
All this information should lead you in one direction to start monitoring the key variables that might bring you your biggest returns and then don’t be afraid of your findings. I can assure you that the OPC Provider, in combination with DMS/DCS, will be an eye opening experience!