Designing a Computer-Based Control System for an Electromagnetic Launcher Facility Using NI Hardware and LabVIEW Software
"We chose a PC-based solution over a programmable logic controller (PLC) because of overall PC flexibility and performance. In addition, some of the required real-time data analyses are too complex and beyond the scope of the PLC but easily accommodated by a field-programmable gate array (FPGA) and the NI LabVIEW FPGA Module. "
- B. M. Huhman,
Plasma Physics Division, U.S. Naval Research Laboratory
Controlling or monitoring 200 data points using computerized process control software and hardware in the electromagnetic launcher (EML) facility at the Naval Research Laboratory (NRL) to ensure consistent and safe operation.
Using National Instruments software and hardware to trigger capacitor modules in the pulsed power system to shape the output current.
B. M. Huhman - Plasma Physics Division, U.S. Naval Research Laboratory
J. M. Neri - Plasma Physics Division, U.S. Naval Research Laboratory
The NRL operates as the Navy's full-spectrum corporate laboratory, conducting a broadly based multidisciplinary program of scientific research and advanced technological development directed toward maritime applications of new and improved materials, techniques, equipment, systems and ocean, atmospheric, and space sciences and related technologies. To create a solution for triggering capacitor modules in the pulsed power system to shape the output current we analyzed each data control point to determine our hardware and software requirements and used four high-voltage power supply units from General Atomics (GA) to charge the capacitors. Each power supply unit (PSU) had digital I/O controls and analog voltage programming with voltage and current feedback. We used fiber-optic signals to trigger the capacitor banks and read the firing status.
In addition, we needed controls for the isolation relays, emergency stop buttons, and safety interlocks. For safety reasons, we connected the external interlock controls of the power supplies to the relay status switch and tied it to the emergency stop loop. The power supply cannot energize the high-voltage output if an emergency stop button is activated, such as a door opening or if the relay is not energized.
Choosing a Control System
We chose a PC-based solution over a programmable logic controller (PLC) because of overall PC flexibility and performance. In addition, some of the required real-time data analyses are too complex and beyond the scope of the PLC but easily accommodated by a field-programmable gate array (FPGA) and the NI LabVIEW FPGA Module. With LabVIEW FPGA, the base clock can implement programming steps in 25 ns blocks.
LabVIEW also satisfied other criteria including simple programming and future expandability. We used the NI Developer Suite with the LabVIEW FPGA and LabVIEW Statechart modules as the core software for process control flow. In addition, we implemented off-the-shelf hardware so that the programmer can write the process control software.
We split the graphical user interface (GUI) into upper and lower sections. The upper half shows voltage and current feedback from the high-voltage power supplies and digital status. The operator can input the analog voltage setpoint and selectively power or disable individual power supplies. The upper right status area determines the state of safety-critical inputs and outputs. The lower GUI half shows the voltage feedback, the trigger generator status, the current state of all 22 capacitor bank isolation relays, and the user-entered bank timing delays. Other data points include trigger generator power status and buttons for different operating modes.
Software Process Control
The control system follows a specific operations sequence, which we defined using the LabVIEW Statechart Module. The module critical safety events can abort the operation if an event occurs outside the normal flow. Depending on the event, the module either ignores or issues an abort command.
NI PCI-6229 M Series Data Acquisition (DAQ) Board
We selected a PCI-6229 M Series DAQ board for the high-voltage power supplies because of the large amount of analog I/O available on the board, including four analog outputs, 32 analog inputs, and 70 digital I/O lines. The analog outputs are optically isolated using an external module, which protects the DAQ board and PC from damage in the event of a power supply fault.
NI PXI-7811R Digital Intelligent DAQ Module with FPGA
The capacitor bank control system is based on the PXI-7811R digital intelligent DAQ module featuring an onboard FPGA chip. This module is housed in an NI PXI-1031 chassis and linked to the PC through a fiber-optic link. One of the key benefits of FPGAs is that they can run multiple simultaneous loops at different clock rates so that high-speed decision loops can run as fast as possible without interruption by a separate task that waits for operator input. Additionally, we connected several NI cRIO-9151 R Series expansion chassis to the PXI-7811R. To provide another safety layer, the operator can add analog and digital I/O modules, which have built-in isolation, to the expansion chassis.
A Rugged Ethernet Controller Interface with NI Compact FieldPoint
The Compact FieldPoint system is always running. Operators use NI Measurement & Automation Explorer (MAX) to look at a live raw data feed and manually operate the relay outputs without running the host PC program. This is a substantial advantage for facility operations because we occasionally need to power a relay or a particular system for a local test.
The voltage feedback from the capacitor banks passes through an external, sacrificial optical isolator that protects against surges before an NI cFP-AI-118 analog input module digitizes the voltage feedback. An NI cFP-RLY-425 relay module drives warning lights, gate and vacuum valves, and controls for powering various devices, and an NI cFP-DI-300 24 VDC digital input module detects the status of various doors and the emergency stop switches.
We encountered a number of issues during development due to the high current generated that creates spikes, noise, and surges. We used several solutions including RC filters, optical isolators, and repositioning equipment.
The facility has fired many shots since coming online, and the NI software and hardware has performed its duties without any problems. We upgraded the system to control additional capacitor banks partway through the shot series. We also made modifications to the CompactRIO hardware, which the NI software automatically recognized, and integrated them into the process within minutes of installation. We knew the upgrade from the start and created program stubs to accommodate the new data points.
The authors would like to thank Ray Allen, Chris Berry, Craig Boyer, Eric Featherstone, Rick Fisher, Aaron Miller, and Dave Phipps for their superb technical assistance.
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