DEWETRON’s data acquisition chassis uses software called OXYGEN for channel configuration control, high-speed data logging, acquisition triggering, and more. OXYGEN can be controlled via the software front panel itself or, behind the scenes, by any software framework using SCPI commands.

For this test application, DMC chose to integrate control of OXYGEN through our custom application framework based in LabVIEW using DEWETRON’s well-documented SCPI commands and their in-house developed LabVIEW wrappers.

OXYGEN Capability

Before highlighting DMC’s use of SCPI commands to control data acquisition, it is worth noting the design decisions behind selecting DEWETRON’s hardware and the corresponding OXYGEN software.

OXYGEN allows users to configure and manage their own test setups by:

• Naming specific hardware channels
• Applying sample rate, units, and scaling to measurement channels
• Creating trigger events that will start and stop recording data automatically
• Configuring logging settings, with log types available in TXT, CSV, TDMS, and more
• Creating digital value displays that update in real time to allow operators to review test data as it is acquired

and, perhaps most notably for our application:

• Creating AC power groups from available configured channels for detailed multi-phase AC power analysis
  • This power group feature automatically calculates and presents highly accurate and detailed data like active/reactive/apparent power, power factor, fundamental vs total power, and more from simple voltage and current measurements on each AC phase.

Having all of these features configurable in OXYGEN and accessible via SCPI commands on the back-end means we can let users configure and control their data acquisition through DMC’s custom LabVIEW application, which also integrates custom test sequencing.

Interfacing with OXYGEN using SCPI Commands

In order to integrate OXYGEN control into our custom LabVIEW application, we first had to dive deep into DEWETRON’s SCPI programming guide to determine the correct commands. Though this is standard practice when creating new hardware drivers, DEWETRON provides a great LabVIEW driver set that exposes basic SCPI control of OXYGEN via TCP/IP. This driver set includes built-in SCPI functionality to:

• Read channel properties
  • Each channel has separate configurable properties that vary based on the type of hardware
• Configure, start, and stop external data streaming
• Query measurement values for one or more channels
• Query system errors

In addition to the basic drivers listed above, DMC developed additional custom SCPI code modules to:

• Create and configure automated OXYGEN trigger events for controlling digital output channels
  • Using the :TRIGger: command set
• Write OXYGEN channel properties like units, sample rate, etc., from the user’s test configuration setup
  • Using the :PROPerty: command set
• Create time-stamped, descriptive data markers when measurement values exceed any user-configured guardrails during testing
  • Using the :MARKer: command set

Integrating OXYGEN Commands into LabVIEW

A question that the reader may have at this point is: Why bother with using LabVIEW at all? Why not just use OXYGEN to do all data acquisition and skip the SCPI commands?

The answer is that integrating with our custom application framework in LabVIEW enables us to use a tried-and-true device control and measurement sequencing architecture and to integrate with a variety of measurement devices from several manufacturers. It also allowed for a custom user interface experience.

DMC is well-versed in test application development in LabVIEW and has developed several in-house LabVIEW toolkits that allow us to present data to our users in information-dense, highly configurable custom applications.

For this project, DMC has used its custom-developed sequencing toolkit based in LabVIEW that allows our users to configure device control and measurement test sequences with custom test limits. Users can use pre-made sequence steps and string them together to create custom automated test routines tailored to their various systems, and manage those sequence files and their revisions, all within DMC’s LabVIEW application. These test routines may reconfigure a device’s settings, turn a device on/off, start/stop data acquisition, continuously monitor safety circuits, and allow the user to pause, restart, and stop execution at any point.

Additionally, integrating remote control of devices like OXYGEN within our LabVIEW application allows us to modify and standardize on things like:

• Error and warning messages to the user from different devices
• Centralized sequence and diagnostic logging from different devices for system-level troubleshooting
• Standardized device control widgets that are exposed to the user
• Simulated devices for testing in non-laboratory development environments

Conclusion

By leveraging the powerful capabilities of the DEWETRON OXYGEN software and measurement hardware via SCPI commands, DMC seamlessly integrated detailed power analysis and high-speed data acquisition from the TRIONet3 chassis into our custom test sequencing application.

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DMC recently integrated a Fluke 726 handheld multifunction calibrator into a turnkey automated test stand. The test system incorporated a large switching matrix connected to multiple test instrumentation hardware components to perform a variety of automated test sequences on our client’s test article.

Multifunction process calibrators are powerful and unique instruments capable of sourcing and measuring more signal types than a multimeter including thermocouple signals, RTD signals, and low current transmitter signals. The Fluke 726 that our customer requested does not have a benchtop or PXI chassis-mountable form factor which made integration a challenge.

Advantages of the Fluke 726

Though handheld devices are awkward to integrate in otherwise very standardized server racks, the Fluke 726 offered our client several advantages over a collection of other, similar rack-mounted devices. The Fluke 726 is already widely used at our customer’s facility, meaning that a calibrated supply of these calibrators is readily available to swap into the test system if needed by the end user. Additionally, keeping the existing equipment allows us to implement the customer’s exact test steps without needing to adapt their tests for new equipment, allowing an easy one-to-one comparison of automated and manual test results.

Power

Unlike most of our automated test equipment, the Fluke 726 is powered with four AA batteries, which posed a unique challenge to integrating it in our turnkey system where most devices run on 120V or 240V power. We opted to integrate a battery eliminator to allow us to power the calibrator with the rest of our system and minimize the downtime of constantly changing the batteries. Our custom-built Power Distribution Unit converts facility power into different voltages for our test instrumentation and sends power to our battery eliminator, allowing the Fluke 726 to power up with the rest of our system and integrate into our emergency-stop safety circuit.

Automated Control

The Fluke 726 is controllable with VISA commands via an RS-232 serial interface. This allowed us to integrate control of the Fluke 726 into our custom application by wrapping these VISA commands into LabVIEW drivers and creating APIs for each of our customer’s desired functions, such as simulating a thermocouple voltage, measuring an RTD signal, etc. These functions are then available to the user for manual control of the device through our application.

Taking it one step further, these LabVIEW drivers are also wrapped into custom TestStand steps which allows us to integrate control of the calibrator into automated test routines and log measurements from the calibrator.

Takeaways

Integrating handheld devices rather than rack-mounted devices is not commonly needed in automated test equipment design, but when it provides value to an end user it can be incorporated as described in this article. Though it was contrary to our usual instrument integration, DMC was prepared to tackle the challenge and created a robust solution that satisfied our customer’s needs and can be propagated to future projects where customers have similar requirements.

Learn more about DMC’s Test and Measurement Automation and LabVIEW programming expertise and contact us for your next project.

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