What DAQ System Should We Use?

Readers help a reader solve this control problem. Next month: How can we measure load profiles?

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4. What am I going to do with the actual data after it is taken? Is it for control, pass/fail, analysis, distributed analysis, or all of the above? Do I need SPC? If this data is selected only for control, storage and analysis tools won't be needed. Often PLC or PC-based PLC systems are good for this type of DAQ usage. If the data is to be analyzed to get a handle on a process, consider a good math or real-time SPC package. But be aware, many analysis packages do not do data acquisition, control, and analysis. If these things interest you, they all can be had in one package.

5. How much data do I need to collect and what do I need to retain? Who will need to access it? If the collected data needs to be retained and shared with many people, consider storage in a central database on the company network. You may find that getting a very standardized system is the best bet. A standard SQL server on a standard PC network is easy to maintain and is usually cheaper.

6. What is the cost-to-benefit ratio confining the project? Basically, figure out what your budget is. Take into account the training and expertise needed to configure and maintain the system.

7. How difficult can this be to setup and maintain? Does our company have the expertise to configure or maintain this, or will we need to outsource? There are many good product out there that are very reliable, reasonably priced and have good features. A good thing to also take into account is how easy it is to set up and maintain. As an example, a USB device takes basically no setup time, it may be plugged in and unplugged at will. No protocols or baud rates need to be set up, it just works.

8. Would a piece-by-piece configuration work or are we better off with a single supplier and a turn-key package? Many companies sell components piece-by-piece for data acquisition and some provide all the components plus the configuration and installation. Determine what make the most sense in your case.

...After these questions are answered as well as possible, the road to a decision on which products are the best fit becomes much more obvious. Kurt Electronics sells multiple hardware and software packages for data acquisition, control, and distributed analysis, both real-time and post-process. We sell components or completely configured systems as specified by the customer. Products include KurtSPC, KurtUSB, the KurtICS, MagNUM CMMs, and the KurtCheck systems.

Jon Baller, Software Engineering Manager

Kurt Electronics, www.kurtelectronics.com

Define Must-Have Data

The first step in selecting a data logging system is to understand the required results. You should have a good understanding of the minimal amount of critical data required to accomplish the decision task at hand. A list of the "must have" data vs. the "nice-to-have" data will establish the priorities. Data overload is costly and typically unnecessary but frequently occurs when surplus data is available.

...Determine the number and types of signal types and the period of time over which the recording will take place. This will result in a count for the total number of samples, which will help to determine amount of memory required to store the resulting data. Then think about all those numbers and ask yourself if they are all necessary. Some may not be.

...Probably the most important need is to understand is the speed at which you must acquire the information and the accuracy of the measurements taken. The type of input and rate of change of that input will determine the acquisition speed. Room temperatures change much more slowly than the load on a shock absorber. You may think that the acquisition speed is self-evident but another review of the system under test as well as the instrumentation may reveal alternative methods of analysis resulting in less data to sort through, saving time and money.

...Assessment of other instrument functionality is another step in the decision process. Many new systems offer an array of features that, at first glance, appear mandatory. A review of the process and goal will provide an understanding of the necessary added features such as expanded memory, multiplexing channels, isolation of inputs, communication options, and alarming features. Buy what you think you will need within the next two years.

...The next step is to understand the operating constraints. Self-imposed constraints include deadlines, test environment, available power sources, persons analyzing the data, and persons operating the equipment. Company-imposed constraints include budget, deadline, authorized supplier, communications methods, and government-imposed: FDA, EPA, OSHA, or other regulations requiring data integrity or security. Know what your constraints are prior to looking for a solution as this will limit the field and expedite your decision.

...Third, consider available solutions and their functional differences. A quick run-down of the available solutions includes portable standalone data loggers, PC-hosted data acquisition boards/systems, chart recorders (paper and electronic), SCADA systems, and portable standalone data loggers.

...Low-cost options include instruments designed for low power consumption to operate from batteries and which have internal memory for data storage. These are standalone data recorders that operate independent of a PC, but will require a PC to either program or analyze the stored data. They are intended for long-term unattended data collection.

...Systems in this category are typically more rugged and able to withstand more abuse, both environment and shock and vibration, for the demands of remote and plant floor applications. Operating temperature ranges and environmental tolerances are wide. Low-cost units typically are designed for a specific input type with low channel count: one to four channels with dedicated temperature, humidity, or contact closure channels is the norm. Factory options include voltage, current, or RTD inputs. A range of samples rates are preselected from the factory and programming flexibility is limited. Accuracy is 8-12 bits and acquisition speeds are in the seconds to minutes range. They are typically considered disposable and are very likely task-specific, i.e. temperature, relative humidity, DC voltage or current, or event recording. Don't look for accuracy or a lot of flexibility, but they are great for the right application.

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