NI LabVIEW and Apple Macintosh Provide Pulse-Radiolysis and Flash-Photolysis Experiment Control

Author(s):
Paul Rijkers - Delft University of Technology

Industry:
University/Education, Research

Products:
LabVIEW,

The Challenge:
Creating a flexible, universal interface for the control of subnanosecond-pulsed radiation sources and high-frequency optical and microwave detection equipment with automated digital data acquisition, storage, and preliminary plotting and fitting procedures.

The Solution:
Using National Instruments LabVIEW to develop and maintain the application, along with Apple Macintosh computers as the platform to create a robust, dependable, and user-friendly interface for the experimentalist who can focus on his or her scientific goal, free from concerns about the operational aspects of the equipment.

The Research and the Application

In the Optoelectronic Materials section of DelftChemTech (a department within Delft University of Technology), we are concerned with the nature and dynamics of excited states and charge carriers formed as a result of radiation and matter interaction. At present, our attention is focused on complex molecular materials, which could form the basis of a new generation of molecular optoelectronic devices for applications in photovoltaic cells, light-emitting diodes, and field-effect transistors (e.g., conducting polymers, self-assembling discotic compounds, and inorganic/organic composites). The radiation sources available include a pulsed 3MV Van de Graaff accelerator and a variety of pulsed UV and visible lasers. We use fast time-response optical absorption and emission and microwave conductivity detection techniques to probe the properties of short-lived excited state or charged intermediates. We are currently constructing a femtosecond laser-driven electron accelerator in combination with ultra short (terahertz) detection techniques.

We created the REACH (radiation chemistry experiments and their computerized handling) application to perform several experiments at different locations using the same user interface. During the startup phase, the experimentalist chooses the setup he or she wishes to use, thus defining the devices that will be initialized for that type of experiment. All devices used have the NI PCI-GPIB as interface to the computer. We made a number of digitizing oscilloscopes available, such as LT374L (Lecroy), TDS680b (Tektronix), RTD710 (Sony/Tektronix), and SCD1000 (Tektronix), to record the experiment data. Their own memory and intelligence is used to average and compress the data to a smart dataset. We incorporated several meters, such as the thermometer-T740 (Keithley), electrometer-617 (Keithley), multimeter-2000 (Keithley), powermeter-8541 (Wavetek), and Labmaster-powermeter (Coherent), to retrieve the relevant parameters. Furthermore, we implemented a number of homemade devices and other instruments (all equipped with GPIB) to control the process.

After the radiation source is triggered, the system collects and processes the transients recorded by the digital oscilloscopes (triggered by the hardware) to provide a meaningful data record. The system reads and processes the data and accompanying parameters, which are then ready for the next measurement. In addition, the system can record up to 500 transients in a single measurement session.

Once started, the application consists of two windows - a main window from which the measurements are made and a plot-data-collect window on which the results of several measurements can be collected in a graphical way so they can be printed. In the main window, the experimentalist can perform some primary data manipulation, but this does not change the recorded data. The system saves each transient on disk as a record in a binary data file. We designed the system so that extensive data manipulation and evaluation is not done in REACH.  We chose this so the experimentalist can choose other applications for additional data analysis.

In the main window, the experimentalist has about 50 functions to tune and perform the experiments. Once activated by the experimentalist (using menu items or free programmable buttons on the screen), these functions are queued after which they are launched. Some functions require that others have been done before, so a specific history of function flow is wanted in such cases. REACH performs such a history of functions automatically by interleaving these functions in the queue. In many cases, a complete measurement session is required to create a dataset spectrum. In such a case, the experimentalist enters the parameters for that session after which REACH processes automatically the entire measurement session by filling the queue with all functions desired for that session.

Because in science the ability to repeat experiments under same conditions - sometimes after many years - is a must, REACH retrieves past experiment data, when old process computers were used. For the same reason, the application can startup and initialize using datasets from old experiments, after which such experiments can be continued or repeated. Also, the data integrity is very important. Once the system saves the experimental data, no other software can change them. REACH protects the data integrity and will warn whenever it notices that the data has been changed. However, it is possible to change the data afterwards for some values using REACH, but it will always store the changed data as a newer version of the old record that cannot be overwritten. In this way, the original recorded experiment data are safe to use for future repeating experiments.

Using LabVIEW as the Development Tool

Using LabVIEW, we created small applications to test and evaluate small parts of the process. As a result, we later integrated the smaller parts into the much larger overall application. Although instrument drivers are available in NI LabVIEW for most devices, we chose not to use them because they are typically written for multipurpose usage and we needed drivers for very specific functions. By writing our own instrument drivers, we avoided overhead in the software and boosted the readability of the program.

For more information contact:

Paul Rijkers

Optoelectronic Materials Section

Delft ChemTech Department

Delft University of Technology

Mekelweg 15

2629 JB Delft

The Netherlands

Tel: ++31 15 2783982

Fax: ++31 15 2787421

E-mail: rijkers@iri.tudelft.nl

 

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