Process Controller Data Acquisition and Analysis

This is part of a series of tutorials. All tutorials up to the previous tutorial should have been completed.

Background

Process Controller can

Step One: Ensure that your Experiment is Set-Up

Make sure that all the valves and connections required to run your experiment are made. Your stamp box should look something like the figure below.

Step Two: Start the Experiment

Before beginning, click on the "Plant Operation" tab. The "Plant Operation" tab allows us to monitor how the experiment is running and provides a quick check for troubleshooting. If the green light is illuminated in this tab, this indicates that Process Controller is communicating with and giving an ON value to either the valve or pump.

In the "Plant Operation" tab set the "Mode of Operation" to "Automatic Operation" meaning that Process Controller will automatically switch states once the rule for switching each state is satisfied.

Next, start the experiment in Process Controller dragging down and selecting the "Operator Selected State" to be "Add Chemical." When you select this state, the plant operation tab should look very familiar to the figure below with the appropriate valve and pump turned ON.

Note: You may encounter problems when running the experiment such as a pump or a valve that is leaking or not working

You should try to fix any problems as they arise and troubleshoot with the experiment and equipment. Don't worry if you spill water, but clean it up as necessary.

As the experiment is running check to ensure that things are working properly.

  • Is the chemical stock tank gradually going down in volume over time in the "Add Chemical" state?
  • In the "Settle" state, are both valves and the pump off?
  • Did the water level decrease in the tank in the "Drain" state?
  • After the "Drain" state, did Process Controller cycle back to "Add Chemical" state?

Step Three: Data Analysis

You only need to complete one full cycle of data collection. The next step is to to open the datalog and statelog that contains your file. Using the file directory where you logged your data i.e. N:\Courses\AguaClara\FlocTube fall09, open the excel file datalog and the statelog for the date of your experimentation.

Step Four: Using the State Log

Ensure that in your state log that you have cycled through the necessary states in process controller. There will be a time stamp of your team having done this.

Helpful Hints for Data Analysis

Utilize your state log to find the time when each state started and ended. This will help you in creating your graph in excel.

In looking at the sample state log, you should notice that the state log will also tell you how the state was changed. Under "Rule that caused the previous state to change," if the label is the next state in sequence then it means that Process Controller software changed the state. If the label was instead "Operator changed the state," that indicates that someone manually changed the state and overridded Process Controller's automatic control.

Data Log

Below is a sample data log in excel. For this experiment we wish to plot the water level height in the tank over one cycle of the experiment (measured in elapsed time), and so we need to think about the important variables to graph in the data log. Pressure as measured by the pressure sensor is highlighted in yellow is "7 kPa" and the time that elapsed is highlighted in red as the "Day fraction since midnight on 9/4/2009" and this is shown in the figure below.

Now that we have identified the variables that we will plot, we need to find the range of time period over which we can plot these values on a graph.

Data Analysis in Excel

Your task is to create a graph of water level height in the tank over one tank cycle. You need to look up the time period for one complete time cycle (i.e. process controller cycled through "Add Chemical," "Settle," and "Drain."

When you have selected the data, convert your time data either into seconds or minutes. Also, set the time to be zero when you started the experiment.

In creating your graph, follow standard format conventions:

  • Do not include a title. If you want to describe the graph, put a caption underneath and begin the caption with "Figure 1." for example.
  • Label your axes and put the units in parentheses.
  • Eliminate any grid lines unless you are in log mode.

An example graph is shown in the figure below. Do not worry if your graph does not have exactly the same values, but it should be close. This tutorial was an exercise of comprehension, not scientific precision.

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