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Electron Microscope Loop Control Using ADwin

ADwin-Gold-II DAQ System Offers High-Speed Control

CAS DataLoggers recently supplied the control solution for a university physics department conducting research using a scanning electron beam microscope (SEM). SEMs generate extremely high-resolution (on the nanometer level) images by focusing a narrow electron beam to scan the sample. Part of the beam is absorbed by the material being scanned, but about 10-20% of the electrons are reflected off the surface. These electrons produce signals (often secondary electrons) which reveal the sample’s surface topography and composition, resulting in amazingly detailed images. In these demanding applications users need high-speed control to achieve the tight precision required for reflecting the beam.

XYZ Piezo Actuator control:

CAS DataLoggers provided the department with an ADwin-Gold-II Real-Time Data Acquisition and Control system. Suitable for controlling all types of scanning microscopes, the ADwin is a high-speed controller housed in a compact metal enclosure. ADwin is ideal for real time XY Loop control of many types of scanning microscopes. Here the ADwin system controls an XY scan of the surface of the sample under the microscope. Using one analog output per axis, ADwin controls the movement of each piezo lienear drive. The ADwin’s integrated analog and digital I/Os provide a very fast response time on the order of 1 usecond or less. ADwin also features a high-speed event counter channel with on-board statistical analysis.

In this experiment the sample is fixed and the beam is moved by two magnetic coils, those being an X and a Y coil. Motion is achieved via piezoelectric actuators at high precision and accuracy. The resultant data is in the form of a 2D grid of data points. Users supply a varying current to the microscope’s focus coil to make the electron beam go deeper or higher: the ADWin-Gold II system controls the beam’s movement using its own tightly-coupled Analog Outputs 1 and 2. The ADwin-Gold-II also features 16 analog inputs, 2 analog outputs, and 2 14-bit ADCs. ADwin can easily achieve 10-20ms precision or even 50ms as needed. Feedback is output in the form of an analog value, i.e. control and data acquisition are simultaneously accomplished here.

Exact Timing with Local Processor:

ADwin’s unique TiCo co-processor is a local processor with a real-time operating system that runs independently from the Windows CPU. With the standard auxiliary processor TiCo meets the highest timing requirements. The independent, programmable DSP can also have its own bus to access all I/Os and interfaces. TiCo is self-sufficient and produces extremely precise signal patterns.

Fast controllers such as the ADwin-Gold are also useful for additional tasks besides the experiment itself, e.g.  temperature control, laser power control, field power control, etc. Any kind of controller can be implemented on ADwin systems.

Ethernet Communication:

ADwin’s customizable design offers a variety of communications options including interfaces for Ethernet, USB, CAN-bus and more. Here the department selected the Adwin-Gold-ENET version with Ethernet interface (10/100 MBit/s) and BNC sockets for analog signals. In this way the ADwin measures the data and also sends it online for in-depth analysis.

Stand-alone DAQ:

The department head also chose the Bootloader option for stand-alone operation without PC. ADwin’s onboard DSP operates independently of the PC or external computer’s OS, ensuring users have the benefits of direct software connection with Windows without the risk of OS lockups and crashes.

Development Tools:

ADbasic provides a fast real-time development tool for ADwin systems. Application development freedom is provided by a full set of available drivers enabling full integration with other applications and programming languages, including an interface library for all of the most common GUI and development packages (VB, VC, Labview).

Application Benefits:

The ADwin-Gold II is a stand-alone data acquisition and control system with fast, local DSP controller and memory, analog and digital I/Os, and Ethernet or USB interface for the communication with a PC. All these functions in a single system is very cost-effective for these lab control applications. This makes ADwin ideal for real time XY Loop control of many types of scanning microscopes. With its rugged, compact metal housing the portable ADwin-Gold is also available in multiple form factors, such as a desktop unit, for panel mounting, or as a portable system in combination with a notebook.