Summertime, ice cream, and data acquisition

Electrical Apparatus, Jul 2004 by Tryling, David P

How an ice cream making machine can lead to an understanding of how data is gathered, organized, and used

ONE OF THE JOYS OF SUMmertime is a big bowl of ice cream. One of the great benefits of using Human Machine Interface, or HMI, software in automation projects is the ability to acquire and store data from the machine or process being controlled. While most engineers and project managers are aware of these capabilities, it is surprising still how few truly take advantage of them. However, with the constant pressure for higher productivity, the use of data acquisition techniques is certainly on the rise. And if you think ice cream and data acquisition aren't connected, wait and see.

So, assuming that we are starting at the beginning, what is data acquisition? A simple definition is gathering and storing events and parameters of a machine or process. A broader explanation includes the organization and use of machine or process information to improve quality, productivity, or profitability.

With these definitions, we are dividing data acquisition into two areas. The first is the actual acquiring and storing of information. The second is organizing and using the information.

Acquiring data

Industrial engineers are trained to understand the manufacturing processes and to analyze the various statistics of machine or process operation. Data acquisition provides a more automated way of collecting the data that industrial engineers have been doing manually for years. These pieces of information often include such things as date and time, machine parameters, errors, quality information, and machine or process event occurrences. Regardless of which software you choose to use for your application, there are some basic types of data that can be stored.

Time

Computers are great devices for developing and recording time. In HMI applications this is called a time stamp. A time stamp in a computer can provide the date, the year, and the time of day down to hundredths of seconds. Once you have data recorded with this level of precision and organization, viewing data by time gains significance.

Events

Think of events as a broad category of "things that happen." This could be an I/O point that means a particular valve or motor is operating. It could be an operator pushing a button on the screen or on the machine to start or stop the operation. It could be a logical event-a sequence of other events happening and creating a logical outcome (event). Recording events, when correlated with time, helps to provide a record of the actions of a machine or process.

Values

Values are mathematical or character-based pieces of information that are related to the machine's operational process. For instance, a value for the level of a tank could be "10," and a second value associated with the first value could be "feet" or "inches." Values may or may not be related to each other, but all will carry a variable piece of information to be stored.

Description

As the word implies, it is important to record the description of an event or value for use in later interpretation. This can be especially important when recording error or alarm information as in "Tank Level High" or "Emergency Stop Pressed."

Now that we have discussed the basics of what we can record in our data acquisition system, the application and use of these basic capabilities begins to become somewhat unique with regard to the machine with which it will be associated.

The ice cream example

For an example here, we will use an ice cream making machine. The important factors in making ice cream are time and temperature, together with ingredients. Therefore, our data acquisition system may record such events as when the batch making process is started by the operator and the time at which each ingredient is added.

It may also record the values for the amounts of the different ingredients that are added and the temperature of the tank. The system may record the name of the ice cream being made in the batch. Each time an event or value is recorded, a line of information is added to the data storage. Each line receives a time and date stamp.

If we want to know how long the batch of ice cream took to make, we can look at the beginning time and date stamp and compare it to the ending stamp. We will know to the closest hundredth of a second how long each batch took to make, and this can be compared to other batches and analyzed.

However, we may only want to know how long the ice cream is mixing, and in this case we would only look at when the mixer motor starts and when it stops. When you get to the second portion of the data acquisition project, that is the organization and use of the stored data, it becomes useful to have stored all of the proper events and values for a meaningful analysis.

Now, understanding the basics, it's important to know that different software packages allow for the configuration of these recording items (events and values) by different methods. While these methods of entry and configuration are different, they also have certain similarities because in most cases they operate within a Windows environment.