"National Instruments hardware and software makes the design and implementation of this prototype system quick, modular, and configurable. It helps create a system that is easily and inexpensively duplicated and modifiable."
- Derek Hopkins, Pacific Northwest National Laboratory
The Challenge:
Creating a flexible and cost-effective alternative to commercial ion trap packages by designing a system that integrates commercial and lab-built components.
The Solution:
Building a control and data acquisition system that we can configure to interface with generic components using NI Measurement Studio software and PCI boards.
Author(s):
Derek Hopkins - Pacific Northwest National Laboratory
Michael Alexander - Pacific Northwest National Laboratory
Kenneth Swanson - Pacific Northwest National Laboratory
Michael Buschbach - Pacific Northwest National Laboratory
Developing a Better System
Ion Trap Mass Spectrometry (ITMS) is used in scientific research ranging from fundamental physics to analytical chemistry. In general, ions are created and injected into a vacuum chamber containing helium at about 1 millionth of atmospheric pressure. An oscillating radio-frequency (RF) field causes the ions to move in stable orbits, trapping them in a small volume. An optional “tickle” waveform fragments molecular ions by forcing them to collide with the helium atoms. As an RF signal of increasing magnitude is applied, ions of increasing mass are expelled from the chamber and strike a detector, producing a spectrum ion intensity vs. mass to charge ratio.
Our goal was to design and prototype an ITMS system using both commercial, off-the-shelf components and lab-built components. Typical commercial systems range in cost from $60,000 to $200,000. By designing a control interface that can drive a set of generic components, an ITMS can be built in-house for about $20,000. If components such as PCs, lasers, and vacuum systems are multitasked with other experiments, this cost advantage is more significant.
An even more important advantage is the flexibility our system provides. The user can choose and build their own components, which allow researchers to customize their experiments. Flexibility in software also is important, so we can collect and analyze data in the most appropriate and accurate format for each experiment. To provide this flexibility in both hardware and software, we created an inexpensive and easily configurable control system.
Integrating Components using NI PCI Boards
The system operates in externally triggered or internally triggered mode. In externally triggered mode, a particle discriminator detects a moving solid particle and triggers an ablation laser to blow the particle apart in the trap chamber. The same trigger signals the NI PCI hardware to start a scan. For analysis of gaseous samples, an electron gun produces ions and the scan is triggered internally.
The purpose of the particle discriminator is to determine the size and speed of particles entering the system. An FPGA chip with a resolution of 80 MHz inputs signals from two detector lasers to determine the speed and calculate the size of a particle. If the particle meets the criteria of the experiment, a trigger is sent to fire an ablation laser. The same trigger is sent to the NI PCI control hardware to start a scan. Once the time sensitive calculations occur, the speed data transfers to a microcontroller that in turn sends it asynchronously to the control software through an RS232 serial connection.
The PCI control hardware consists of four National Instruments PCI boards － a NI PCI-6110 simultaneous-sampling multifunction DAQ board, NI PCI-6602 counter/timer board, NI PCI-5411 arbitrary waveform generator board and a NI PCI-5401 function generator board.
The multifunction I/O board (MIO) is central to the system operation. A scan starts when the MIO receives an external or internal trigger. One onboard counter circuit generates a scan gate off this trigger, while the other generates the scan clock. Both of these signals are routed to the NI RTSI bus for synchronization with the other boards. The RF output waveform is generated by the MIO, controlled by the scan gate, and driven by the scan clock. The MIO also acquires the analog spectrum signal. Finally, one of the DIO lines handshakes with the Particle Discriminator to deactivate it while a scan is in progress. Note that scans trigger continuously, and there is no reconfiguration between scans.
The NI PCI-6602 counter/timer board provides the rest of the timing signals. Driven by the scan clock signal received from the NI RTSI bus, it generates the electron gun gate and the acquisition gate. Note that this acquisition gate is used to control the hardware to release ions to the detector and to gate the analog input on the MIO.
The arbitrary waveform generator provides the tickle waveform. This wave is triggered by the scan gate signal on the NI RTSI bus. Finally, the function generator board provides a sine wave to the RF amplifier. The needs of the experiment determines the frequency and amplitude of the wave.
The control software was written in Visual Basic 6.0 to take advantage of its Rapid Application Development (RAD) environment and compatibility with NI Measurement Studio. Both are conducive to the goal of creating flexible, easily configured software.
Low-level functionality of the ion trap system, including all interaction with the NI PCI hardware, is encapsulated in an ActiveX control developed for the project. This control exposes a high-level of programming to the user interface (UI). The UI presents the functionality of the system as a collection of graphical elements through which the user sets parameters that drive the mass scan and data acquisition cycle. The UI is currently implemented as a stand-alone executable, but we will soon implement a distributed Client/Server system.
Saving on a Configurable Control System
This system has several advantages over packaged ion trap systems. It costs an estimated $20,000 as opposed to $60,000 to $200,000 for a commercial system. Second, because the user can modify both hardware and software components, they can customize the system to each particular experiment.
National Instruments hardware and software makes the design and implementation of this prototype system quick, modular, and configurable. It helps create a system that is easily and inexpensively duplicated and modifiable. Universities and labs with limited budgets can build on this system to provide flexible, low-cost ion trap experiments.
For more information, contact:
Derek F. Hopkins
902 Battelle Blvd, PO Box 999
Richland, WA, 99353
Tel: 509-376-0591
Fax: 509-376-0420
E-Mail: derek.hopkins@pnl.gov
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