A NASA laboratory employed a notebook-PC-based data acquisition system to gather data for atmospheric research. The notebook-based system helped reduce the size, weight, and cost of the airborne test application, while concurrently increasing its performance, data storage, and display capabilities.

Application Summary
A NASA research lab developed a tracking sun photometer to obtain accurate, multispectral atmospheric extinction measurements at various altitudes. The sensor is mounted through the aircraft fuselage for an unobstructed view of the sun, while the delicate instrumentation remains protected inside the aircraft.

The sun photometer’s solar tracking system is designed to track and acquire data with great accuracy even during aircraft movement. Its cylindrical detector module contains six silicon photodetectors, a sun tracking sensor, and a temperature sensor for controlling the environment inside the module. Its mechanical drive train incorporates stepper motors, which are suited for use with digital control systems.

Approximately every two seconds, the data acquisition system connected to the sun photometer samples sensor data; synchronizes it with other altitudinal, longitudinal, and latitudinal data provided by the aircraft data system; and saves the acquired data to disk.

The acquired data (including photodetector input such as temperature, tracking error, sun azimuth angle, sun elevation angle, and UTC time) is software processed, permitting the system to display Langley and optical-depth 3D plots in near real-time for in-flight feedback.

Original Solution
The original data acquisition system was based on a Hewlett-Packard HP9816 computer. The HP9816 was equipped with floppy disk drives and a printer, and employed an HP 12-bit multiplexing A/D converter and digital I/O to control the sun photometer’s position and collect data from its sensors.

Unfortunately, this rack-mount configuration had several disadvantages for airborne data acquisition.

For example, it:

• was heavy, which increased fuel costs
• was bulky, and thus needlessly consumed valuable cabin space
• required AC power
• inadequately displayed data (i.e., the HP9816 was unable to display real-time graphics)

Also, advances in portable PC technology were threatening to render the HP9816 obsolete.

IOtech’s Solution
Because of the drawbacks previously described, the customer elected to replace its old system with IOtech’s DaqBook, a notebook-PC-based portable data acquisition system. The new system weighs under 20 pounds (including battery pack) and occupies a fraction of the space of the old one.

Furthermore, the DaqBook is battery operable, permitting it to function independently of the aircraft’s power system, an important consideration in airborne applications. The new system’s notebook PC features a large hard drive, enabling the acquisition and retention of more data than was possible with the HP9816. Also, in contrast to the HP9816, the notebook PC can display high-resolution real-time graphics.

Standard features of the DaqBook play key roles in this application. Programmable digital I/O lines prove valuable for controlling stepper motors that run the drive train.

Data is viewed in real time, but with the DaqBook’s parallel-port pass-through mode, hard-copy reports can be printed during the actual data acquisition. Also, reporting from gathered data is easy due to DaqView’s ability to save data in a spreadsheet compatible format.

Conclusion
The DaqBook’s considerable cost and weight advantages have allowed the NASA research laboratory to maintain a cost-effective in-flight test program.

See complete application information in PDF format.