Application areas: educational institutions
Challenge: To build an Internet-based distributed network virtual laboratory system to enable remote sharing of experimental data and equipment.
Application Solution: Using NI's LabVIEW, IMAQ Vision, and other software, along with hardware such as ELVIS, IMAQ-1422, PXI-1000B, PXI-6070E, PXI-5102, SCXI-1000, SCXI-1320, and SCXI-1125, an Interntet-based distributed network virtual laboratory system is constructed. This system enables remote sharing of experimental data and instruments, providing a professional experimental teaching platform for university students and addressing the shortage of teaching resources caused by the expansion of higher education enrollment.
Products used: LabVIEW6.1 (FDS), IMAQ Vision, ELVIS, IMAQ-1422, PXI-1000B, PXI-8176, PXI-6070E, PXI-6071E, PXI-5102, PXI-2501, PXI-7344, SCXI-1000 , SCXI-1320, SCXI-1125
introduce
Extending virtual instrument technology to network applications can better leverage its advantage of "software being the instrument," and will further facilitate the formation of a distributed network measurement system, enabling remote sharing of data and instruments, thereby providing services for experimental teaching and remote measurement and control.
This virtual network laboratory uses a BSDA architecture and consists of four modules: client, web server, application server, and experimental equipment. It features a short development cycle and low cost, while also possessing strong compatibility and scalability. This greatly improves the efficiency of instrument use, avoids unnecessary duplication of investment, and is highly suitable for experimental teaching and research in higher education institutions, with a very broad application prospect.
Abstract: Virtual Instrument Technology being applied to network construction can develop its precursor-“The Software is the Instrument” and help to form distributed network measuring system to accomplish data and instruments sharing for experiment teaching & learning or distant test control. This Network Virtual Lab presents a BSDA construction including client, Web server, application server and experiment instruments four modules. It characterizes short development cycle and low cost together with compatibility and expansibility, which can enhance the utilization efficiency of instruments and avoid unnecessary repetitive investments. Distributed Network Virtual Lab fits the experiment teaching & learning and research in colleges and universities and owns its extensive application prospect.
1. Introduction
A virtual network laboratory is a center without walls. Through a computer network system, researchers or students can collaborate with peers anytime and anywhere, without being restricted by time and space, sharing instruments and equipment, data and computing resources, receiving remote guidance from teachers, and engaging in mutual discussions with peers.
Because virtual laboratories enable remote sharing and even remote control of instruments and equipment across time, space, and disciplines, they meet the requirements of distributed experimental systems in scientific research and teaching, while also addressing the challenging issue of limited teaching resources. Many research institutions abroad have already made relevant and beneficial attempts in this regard. Successful examples include Carnegie Mellon's Virtual Lab at Carnegie Mellon University, a Virtual Engineering/Science Laboratory at Johns Hopkins University, and Engineering Laboratories on the Web at the University of Tennessee at Chattanooga.
Most online virtual laboratories use a client/server (CS) architecture, and can be broadly categorized into three types based on their functionality:
① Software-shared network virtual laboratory. Its characteristics include: the server shares a local virtual laboratory simulation software platform, accepts experimental requests from clients, analyzes and processes experimental parameters, performs calculations and simulations, and finally returns the results to the client. The entire system does not involve specific experimental instruments or hardware; it only utilizes software to simulate the experimental process.
② Instrument-sharing network virtual laboratory. The server also accepts experimental requests and parameters from the client, configures the connected experimental instrument hardware using the experimental parameters, conducts the experiment using the experimental instrument hardware, and returns the experimental results to the server, and finally back to the user, realizing the sharing of experimental instruments and experimental data.
③ Remote-controlled virtual laboratory. The biggest difference between a network virtual laboratory and an instrument-sharing virtual laboratory is that, in addition to sharing experimental instruments and data, it also enables remote control of experimental instruments and equipment by the client.
2. Implementation Principles of Network Virtual Laboratory
The construction of online virtual laboratories often uses the BSDA (Browser/Server/Database & Application) structure, which is a client/server/database/application structure, as shown in Figure 1.
A typical virtual network laboratory consists of four parts: a client, a web server, an application server, and experimental equipment. The web server's main functions are to provide web access services, user authentication management, an open interactive experimental environment, and the generation of dynamic web pages; the application server's main functions are to control and manage experimental equipment, and to collect and process experimental data; and the database's main functions are to assist in user account management, dynamic web page generation, and the storage and management of experimental data.
3. The Composition of a Virtual Online Laboratory
This online virtual laboratory mainly consists of two parts: simulation and real-time measurement, as shown in Figure 2.
The simulation section primarily handles verification and principle demonstration experiments. Using LabVIEW's built-in web publishing function, a webpage embedded in the experimental platform is generated directly on the web server. Users can access the virtual lab via the Internet using only a web browser to conduct experiments. The real-time measurement section mainly handles instrument sharing and remote control experiments. It includes a multimedia auxiliary module that virtually presents the actual experimental platform interface, allowing students to operate it before entering the real-time measurement module. This serves to check students' pre-learning and familiarize them with the experimental content and procedures. The real-time measurement module itself is the core of this section, responsible for collecting local experimental data and analyzing, storing, and displaying it according to the remote user's requirements. This can be implemented using LabVIEW's web publishing function or by using the LabVIEW-based Application Server module and client API module to achieve network interconnection and data communication, enabling remote experiments.
4. Hardware Structure of the Network Virtual Laboratory
We are using a hardware architecture based on the NI-PXI architecture, and a Dell PowerEdge4600 as the web server, as shown in Figure 3.
The Dell PowerEdge 4600 web server is equipped with two Intel Xeon 2.8GHz processors, 2GB ECC DDR RAM, 3×36GB SCSI RAID (redundant disk array), and a Broadcom Gigabit NIC, fully meeting the requirements of multi-threaded, high-volume, and high-bandwidth applications.
The application server uses a PXI-1000B chassis, embedding a PXI-8176 controller and PXI-6070E and PXI-6071E multi-function data acquisition cards for high-speed digital-to-analog conversion, digital-to-analog input/output, and data acquisition. A PXI-5102 high-performance oscilloscope card generates signals, providing a stable and reliable signal source. A PXI-2501 matrix module enables automatic switching between different measurement components to meet the diverse measurement requirements of remote users, achieving measurement versatility. A PXI-1422 image acquisition card extracts images of PCB boards and IC chips, meeting the needs of circuit inspection and IC design. A PXI-7344 motion control card extracts parameters and tracks the status of motor servo systems.
An SCXI-1000 chassis is embedded with SCXI-1320 and SCXI-1125 signal conditioning modules, which are used to amplify, reduce noise, and filter micro-current and voltage signals in microelectronic systems to maintain the high accuracy of the entire system.
A state-of-the-art NI-ELVIS is used to establish experimental models, build experimental circuits, construct small electronic circuit systems, and realize remote sharing of electronic circuit experiments.
5. System Design and Technical Implementation
5.1 Simulation Section
In the simulation section, we use LabVIEW's built-in web page publishing function as a basis, design web pages using HTML, and use Microsoft IIS 5.0 publishing function to directly generate WWW web pages embedded in the experimental platform on the server side. Users only need to use a web browser to access our site to conduct experiments via the Internet. The principle is shown in Figure 4.
LabVIEW's built-in Remote Panel Connection Manager is used to monitor and schedule user activity. NI Web Server analyzes and calculates the experimental data according to the experimental data specified by the remote experimenter, and finally displays the experimental curves and results. The experimental results are then embedded in the generated HTML webpage. Users can simply use a browser to display the experimental data and curves in real time, and complete subsequent tasks such as report generation.
5.2 Real-time Measurement Section
For real-time measurement, we used two implementation schemes to meet users' requirements for remote experiments under different circumstances: one is a Browser & NI Web Server architecture, and the other is an Application Server & API architecture. We used a PXI-1000B chassis and embedded PXI cards as the NI Web Server and Application Server.
The Browser & NI Web Server architecture is based on simulation implementation. It connects the corresponding DAQ and SCXI hardware to the NI Web Server, which in turn connects to the actual experimental instruments to realize data communication between remote clients and experimental instruments, and to complete the remote sharing of experimental instruments. Its principle is shown in Figure 5.
This architecture is suitable for thin client systems. Clients do not need to perform calculations or analyze data; they only need to install an internet browser to receive the data stream transmitted by the server to conduct experiments. It is convenient, simple, and efficient. However, it has relatively high requirements for the server's computing power, bandwidth, and stability under multi-threaded conditions. At the same time, since only one user is allowed to have control at any given time, it is more suitable for remote control experiments.
The Application Server & API architecture is programmed using LabVIEW, based on its built-in TCP/IP module. It constructs an Application Server and an API user terminal, with the TCP/IP module handling network interconnection, data communication, and fault tolerance. The Application Server collects and transmits experimental data, manages users, and records user activity; while the API user terminal provides a GUI interface for operators to acquire, analyze, process, display, and store data. Its principle is illustrated in Figure 6.
This architecture requires API user terminals to download experimental data collected by the Application Server board to their local terminals for analysis, calculation, display, and storage. In addition to high requirements for network bandwidth and stability, it also places high demands on the computer performance of the API user terminals. It is suitable for remote software sharing and instrument sharing experiments and can realize multi-user broadcast sharing of experimental data.
The following section uses a semiconductor transistor DC characteristic test experiment as an example to introduce the implementation method of LabVIEW programming with the Application Server & API structure.
Users are first presented with a multimedia simulation interface to check their preparation and familiarize themselves with the actual instrument operation. As shown in Figure 7, using a graphical panel of an actual instrument, we simulated the DC characteristic test curve of a transistor using LabVIEW. Users can use knobs and various switches to understand the specific content and steps of the experiment, just like operating the actual instrument.
After the simulation is complete, press the "Enter Measurement" button to access the real-time measurement panel, as shown in Figure 8. The toolbar at the top of the panel allows for mode selection, parameter settings, and data storage, while the central area displays the experimental curves.
The main program flowchart is shown in Figure 9. The client API module first sends user information and experimental requests to the server. After the server verifies the request, a TCP connection is established. The server then receives the experimental parameters from the client and initializes the experimental instruments. The server collects experimental data and sends data packets through the TCP/IP protocol. The client receives the experimental sampling data, inserts it into the measurement array according to a certain data format, and displays the waveform synchronously. After all experimental data is collected, the server sends an end message and then disconnects the network connection, completing the experiment.
Figure 8 shows the Ic-Vce curve of the local transistor in the CCMS laboratory measured remotely by the client. Figure 10 shows the calculated value of the transistor amplification factor β and displays the β-Ib curve in real time. Users can select the save button to save the experimental data in the required format, perform corresponding calculations, generate an experimental report using HIQ, and finally complete the experiment.
6. Results and Conclusions
With the support of NI's university program, we have received strong technical assistance. We have established over a dozen experimental systems based on the Electronic Science and Technology major, forming a preliminary prototype of a cross-temporal, interdisciplinary, and cross-platform network virtual laboratory. This provides professional experimental courses for undergraduate students in our department and has been demonstrated online at Huazhong University of Science and Technology's Wuchang campus, achieving remote sharing of experimental instruments and remote experiments, with excellent results. The network virtual laboratory based on the NI virtual instrument platform has a short development cycle, high efficiency, strong scalability, and low cost, making it an effective way to address the resource shortage caused by the current expansion of higher education enrollment.
