Updating an obsolete LabVIEW-based system for measuring solar irradiance

Client – California State University at Northridge (CSUN)

Challenge

Our client had over 4 decades of data on solar irradiance (the amount of light our sun emits). Over that decades-long time span, equipment suffers breakdowns and needs repair or replacement. We were called in to replace that old system with an upgraded system.

For this obsolescence upgrade, the solar irradiance measurements, before and after the equipment change-over, must compare to provide continuity in the measurements.

Consequently, our replacement system had to be checked against the existing system before it went completely defunct.

To that end, we needed to continue making the light measurements with the existing linescan photodiode array. This linescan device required some low-level digital signal control and handshaking to initialize and perform the measurement data collection.

Solution

The prior system used obsolete hardware from National Instruments (NI) such as an E-Series card multifunction data acquisition card and a TIO-10 timer-counter card.

Beside being obsolete, this hardware used on old computer bus. The combination of these defunct features was addressed with a new PC and data acquisition hardware.

Furthermore, some support components were also needing upgrade, such as a non-functional power supply.

We also upgraded a circa 2013 LabVIEW application and added some new functionality. Luckily, the CSUN team had the source code.

All these components were delivered as a turnkey system to CSUN.

Benefits

Obsolete measurement system update – enabled essentially unbroken measurements of solar irradiance over the nearly 40 years coupled with some overlapping data collection for comparison of previous and present data gave confidence that the upgraded system could continue to collect important solar irradiance data for many years to come.

The sun’s output does vary cyclically about +/- 0.035% on average following the sunspot cycles about every 11 years. Check out the plot of solar output over the past about 25 years in this link: https://spacemath.gsfc.nasa.gov/sun/Earth8.pdf

How we worked together

CSUN researchers connected with us after they reviewed our capabilities on our website and had a subsequent conversation. Although the CSUN team had a very good technical understanding of the required upgrades, they were not experts in automation systems and were looking for a system integrator for help.

From our perspective, all the details about the operation of the existing system would be in the LabVIEW source code and electric / signal system schematics. As mentioned earlier, CSUN did have the source code. Some older schematics needed a bit more digging by us to identify all the relevant hardware.

Our proposal was based on this system information and one or two clarifying discussions. CSUN accepted and funded our proposal and we began the upgrade effort.

We didn’t have access to some parts of the system, such as the linescan array, so we tested the completed upgrade as much as we could at Viewpoint and then scheduled a trip to CSUN for the final installation and commissioning.

Once on-site at CSUN, the only surprise was a power supply that wasn’t functioning as expected. CSUN replaced that unit while we were on-site. After all the upgraded components were in place, the system was tested and commissioning was completed successfully.

System Overview

CSUN uses two Cartesian Full Disk Telescopes (CFDTs) to measure solar irradiance. These telescopes can measure irradiance at various specific wavelengths of light. Measurements are made daily and compared with space-based measurements.

Specifically, comparisons are made between irradiance measurements obtained from instrumentation on the SORCE satellite with the measurements obtained from CSUN’s ground telescope-based measurements. The space- and ground-based equipment measure different ranges of light wavelengths. The SORCE measurements span a wide range of wavelengths. This satellite was launched in early 2003 and its mission was completed in early 2020 (https://lasp.colorado.edu/sorce/). Note that SORCE measurements do not have to contend with Earth’s atmosphere.

The CSUN equipment measures at a few specific wavelengths. Comparisons between the two methods is important because satellites don’t last forever, necessitating ground-based equipment that is confirmed from space-based measurements. And, of course, ground-based measurements must contend with Earth’s atmosphere, so correction factors must be calculated and confirmed. Assessing the validity of long-terms trends against shorter-term space-based data lends assurance to ground-based equipment measurement. The nearly 40-years of continuous CSUN measurements can proceed into the future with confidence.

The system we deployed replaced the obsolete equipment and software with:

• new measurement hardware,
• a workstation,
• and a failed power supply.

The application software was upgraded as well to:

• bring it up to the current LabVIEW version,
• add some new functionality,
• and Interface the linescan imager with the upgraded USB-based measurement hardware from NI.