Testing Instruments with NI Measurement Studio and Microsoft Visual C++

Author(s):
Grant Johnson - LECO Corporation

Industry:
ATE/Instrumentation

Products:
Measurement Studio,

The Challenge:
Interfacing with a different department’s existing code to monitor and display functional test data.

The Solution:
Creating a test station running National Instruments Measurement Studio on top of the existing Visual C++ code.

LECO Corporation serves dozens of industries with analytical instruments and spectrometers. Currently, our test department performs strictly functional tests both on the board level, as well as the system level. Because our volumes are relatively low, dedicated in-circuit testing is not an affordable option. Using Measurement Studio LabWindows /CVI as the basis for our functional testers, we can create fixtures that simulate instruments, so we can avoid using actual instruments as test stations. When we place a unit under test (UUT) onto our fixture, it thinks that it is in a particular section of an instrument. If the UUT proves to be faulty, then we repair it. However, we really save money when the UUT causes a catastrophic failure. If damaged materials result from the test, then we need to repair our relatively simply fixture rather then an expensive instrument.

Our research and development team of software engineers develops in Windows using Visual C++. Because we are more accustomed to using C-based languages, such as LabWindows /CVI, using code from our own software department was a challenge. Through the use of National Instruments Measurement Studio however, we now can bridge this departmental gap with the included Visual C++ tools.

Analyzing a Range of Materials -The Application
At LECO, we work with a variety of instruments ranging from analytical instruments, such as protein and carbon analyzers to mass spectrometers. One of the tests that some of our analytical instruments perform on a given sample is the infrared (IR) test, which takes place in an IR cell.

Basically, we vaporize the sample and use infrared light to analyze the density of molecules present in the resulting gas. To gather accurate measurements, we must have IR cells on which we can depend.
To verify the integrity of our IR cells, we perform a drift test as well as a noise test. The drift test (shown right) lasts for three hours during which we monitor the cell output while flowing helium through it. We want to ensure that the voltage does not dip below a certain set point. If the cell voltage steadies above the failure range, then we perform a noise test (see next page). Here we take data for 20 s and check if the peak-to-peak voltage is within a given threshold.

Our software developers using a combination of Visual C++ and Assembly had established all the communications in the instrument. Each application board in an instrument has a daughter board that signs the board onto the Eclipse network and then handles all the transferring of data. To monitor the individual IR cell outputs, we needed to simply tell the A/D on the cell to convert and then read the resulting voltages. Once we had the voltages, then we could plot them to a graph. Visual C++ does not have a graph tool, so we needed to use one that our software developers created. This meant we would require even more software developer help to use their graph effectively. National Instruments came to the rescue with Measurement Studio. Using their graphing tool, it was easy to grab the data and plot it. Suddenly, the most complicated part of the project, the actual display of the data, became the easiest. We were easily up and going in a day with a professional visual representation of the data, with little Visual C++ knowledge required.

NI Measurement StudioAdapts to Environments
Because we can write code in Visual C++ with the help of Measurement Studio, I can ask the software engineers for help in a familiar environment. For this project, I started with their code and used the Translation Wizard inside Measurement Studio to convert it to a Measurement Studio project. The software engineers did not have to know anything about the Measurement Studio C++ tools I was using to help me write the code.

Using Measurement Studio, we have reduced the cost to software developers from 50-60 total hours to more like 8-10 total hours. I can now easily test software written in their environment, Visual C++, with my tools in Measurement Studio. With NI products, I can get the needed results right away and worry about fine-tuning tests later.

For more information, contact:

Grant Johnson

Test Engineer

LECO Corporation

3000 Lakeview Avenue

St. Joseph, MI 49085

Tel: (616) 985-5722

E-mail: grant_johnson@leco.com.

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