Using NI Software and Hardware to Develop a Distributed, Networked Real-Time Control and Data Acquisition System

Author(s):
Randy Schmidt - NexGen Automation

Industry:
Government/Defense, Aerospace/Avionics

Products:
LabVIEW, PXI/CompactPCI, LabVIEW Datalogging and Supervisory Control Module

The Challenge:
Developing a distributed real-time control and data acquisition system that integrates hundreds of transducers and actuators with secure system access, configurable data logging, data extraction, and display features.

The Solution:
Using off-the-shelf hardware from National Instruments, including NI PXI real-time controllers and I/O modules, with National Instruments LabVIEW, the NI LabVIEW Real-Time Module, and the LabVIEW Datalogging and Supervisory Control (DSC) Module to implement a fully integrated and user-configurable, real-time control solution.

At NexGen Automation Experts, we provide state-of-the-art test, measurement, and control systems to increase efficiency for our customers and improve the quality of their products and services.

One of our customers, Wyle Laboratories, required networked, distributed operation along with real-time control and flexible configuration capabilities for a thermal vacuum chamber. We were able to address all of Wyle’s system requirements with cost-effective and flexible technologies from National Instruments.

Implementing the System

We created a chamber data acquisition and control system to collect and display up to 256 channels of real-time data from thermocouples and vacuum gauges, as well as control and monitor up to 192 digital I/O channels for controlling compressors, valves, and pumps. We designed the system to communicate with third-party controllers such as the Omega CYD218 temperature controller and a variety of liquid nitrogen (LN₂) control systems. The control logic is a self-contained queued state machine that provides thermal vacuum chamber and test specimen safety monitoring. The interlock control logic is based on using the control valve, motor, and pump states in conjunction with pressures and temperatures. The state machine architecture offers users easy interlock control state modification during chamber test and assembly.

The proportional integral derivative (PID) control system simultaneously controls and displays 64 analog output-controlled PID temperature control loops and 12 digitally controlled LN₂ PID temperature control loops. The user can make real-time changes to the setpoints and control parameters with this system, which is also responsible for monitoring an additional 100 thermocouples attached to the user’s unit under test.

The real-time and host applications are based on the state machine architecture. With this architecture, the user can easily modify the main program logic by adding new software features or making changes to the hardware. The design goal was to decompose a complex, event-driven application into a set of states connected by queues. This design decouples event and thread scheduling from application logic. Decomposing services into a set of states also enables modularity and code reuse.            

An initial estimate of the tasks for which users can implement this application includes:

·         DAQ Loop – acquire and scale analog and digital data

·         Comm Loop – transmit DAQ and system state to host PC

·         Incoming Command – receive and decompose commands received from the host PC

·         Control Loop – perform real-time command and control

·         LabVIEW Functional Globals – global data storage for real‑time application

We ran the host applications using LabVIEW with the LabVIEW DSC Module. Networked PCs running Windows XP host these applications. We implemented a redundant network using switches, routers, and multiroute cabling, and we used the UDP/IP protocol to broadcast messages to all attached computers.

Taking advantage of its built-in abilities to perform user access security through the user manager and security features, we used the LabVIEW DSC Module to handle all user access issues for all applications on the network. We also used the Tag Engine to facilitate rapid and easy storage as well as display the data acquired by the real-time controller.

Through VI servers, the host application(s) implemented stand-alone applications so the user could view the system states and data on multiple screens.

We built multiple operator consoles with LabVIEW so the user can deploy the consoles anywhere on the local network. These applications run on PCs using Windows XP. Internet and intranet users gain access to the application data by running LabVIEW applications that connect to the DataSocket server publishing the data for remote viewing.

Intuitive and Hierarchical Access

Using the LabVIEW application, the system can build disk resident configuration sets with intuitive and hierarchical access to system hardware. Configuration changes dynamically load to PXI controllers and become effective immediately.

Real-time code in the PXI modules handles deterministic system control. The code also provides the transducer data to an acquisition application running on the server machine. The server collects data from serial devices and updates the panels prior to logging the data to the Citadel database. Alarming, deadband for logging, and defining computed data values are some of the features available through the data acquisition and logging part of the system. Through LabVIEW VIs, the user can take advantage of configurable data extraction and viewing with historical, real-time trend graphs and tabular data display.

The system operates in distributed, networked modules where users have password protection and hierarchical access to the single test facilities for all of the control and data viewing operations.

By using off-the-shelf hardware from National Instruments with powerful software tools, we were able to implement a fully integrated and user-configurable, real-time control solution for our customer.

For more information, contact:

Randy G. Schmidt

NexGen Automation Experts, LLC

14 Monarch Bay Plaza #271

Tel: (949) 510-3043

Fax: (949) 215-5135

E-mail: rschmidt@nexgen-automation.com

 

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