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The Challenge

Develop a software system able to perform rapid, synchronized data acquisition across a distributed network. Very short  experimental times existed, with low tolerance for jitter between sampling areas. Due to the violent nature of mine  explosions, the application required a reconfigurable and robust system. 

The Solution

Using a distributed real-time and field-programmable gate array (FPGA) architecture on CompactRio (cRIO) systems across  a fiber optic network, DSA was able to perform synchronized triggering and data acquisition with timing precision of one  millisecond. FPGA flexibility allowed multiple sensor configurations between platforms, while using the same program  architecture. 

Abstract

A government agency needed a more robust network system for recording test explosion in experimental mines. A fiber optic  network replaced the fragile and high maintenance copper wires that previously ran from every sensor, hundreds of feet, back  to the surface. DSA used the rapid processing power and flexible configuration of the CompactRIO platform to deploy  hardware to each data station, able to readily communicate date back across the network to the host computer. The  CompactRIO combined the needed data acquisition with relay actuators and built-in networking capability to enhance and  improve the previous system. 

The Real Goal: Safety 

When considering difficult applications it can be easy to get caught up in the technical aspects of the job at hand, but the real  goal of the government work was in this case very simple: Save lives. Mine explosions have always been – and continue to  be – a major hazard when people go underground to earn a living. However, in order to develop the safety equipment and  mining disaster rescue procedures that save lives, you have to understand the chaotic conditions within a mine explosion (Figure 1). To gain this knowledge, a government agency has an experimental mine, where it can set off simulated explosions  and monitor the results remotely. 

Figure 1 – An explosion escapes from the experimental mine. 

Extreme environment 

The data gathering system for these simulated mine explosions must be capable of monitoring as many as 64 channels of data  from as many as 40 locations, hundreds of feet underground. Initially the system utilized copper wire to connect the diverse  network of sensors to a central computer. However, the effort required to maintain the continuity of each wire proved to be  extremely costly. To reduce this cost Data science Automation (DSA) replaced the network of copper wires with a fiber optic  network interconnecting the data gathering stations. All that was now needed was a scalable acquisition system capable of  withstanding the explosive forces within the mine. 

Hardware selection 

Due to its robust nature, the CompactRIO FPGA platform lends itself well to the process of gathering data from within the  mine. In addition, the 40 MHz processor allows rapid communication and triggering of the systems over the network. Each of  the 40 data gathering stations deployed in the mine has its own networked cRIO 9014 sitting on a 9104 FPGA 8-slot  backplane.  

The extreme speed of the explosions requires the full capabilities of the cRIO, sampling at much higher than the typical 1000  Hz limit of other competing acquisition systems. The speed of the cRIO also allows it to react to a network wide trigger  within 5ms – thus allowing very tight synchronization of all the data gathering systems. 

Communication and Triggering 

To support fast response to commands and file transfer across the network to and from the host PC, the application leverages  LabVIEW built-in connectivity to implement a low-overhead UDP-based communication protocol (Figure 2).  

Another complication for which LabVIEW provides an elegant solution is configuration of the data gathering systems. Each  of these systems has different requirements for data recording, which often vary from test to test. The inputs include  thermocouples, pressure sensors, light sensors and gas quality sensing. The flexibility of the FPGA allows for dynamic  configuration changes as different cRIO modules are used for each test, merely with the exchange of a new FPGA bitfile and configuration. In addition, the cRIO relay module is utilized for remote calibration of the sensors. This module replaced  another full set of copper control wires previously used for relay functions. 

Figure 2 - The FPGA data gathering code on the remote cRIO system, along with the host PC UDP communication code 

Tying it Together 

Thanks to the flexibility and power of the National Instruments product base, NIOSH has a tool that will gather the data  necessary to accurately gage the effects and propagation of underground explosions. And at the end of the day, if that means  even one miner gets to go home that otherwise might not; it’s been more than worth the effort.