A New Advance in Hydrogen Sensors
T. Anderson, et. al., University of Florida, Department of Chemical Engineering¹

Researchers from the University of Florida, Gainesville, and their colleagues have demonstrated a new working system of wireless hydrogen sensors. The sensors, made of commercially available components and specialized sensing materials, are reliable and accurate and have been combined with a user-friendly alarm system that can contact emergency responders.

The Technology
Specialized GaN-based devices with Pt as the sensing metal are used, allowing the system to achieve hydrogen detection at the parts per million level with very rapid response time (within a couple of seconds) and rapid recovery. The system uses Zigbee-compliant transmission protocol because it is designed for sensor networks and can support more wireless nodes than any other standard available on the market. The network can support up to 750,000 nodes, which would be suitable for city-level deployment.

The wireless sensor node consists of the sensor, power management system with back up batteries, and a Zigbee-compliant wireless transceiver. The base station consists of a high sensitivity receiver and intelligent monitoring software that does basic data logging and tracking of each individual sensor. It is able to warn the user of potential sensor failure, power outages and network failures. This is especially useful in facilities for hydrogen storage, hydrogen-fuelled automobile dealerships and future home garages with hydrogen vehicles, and manufacturing plants, where a number of sensors, possibly with each detecting different chemicals, would be required.

The system can be implemented to act as a real time warning system to 911 centers so that the emergency services are able to act immediately to contain any potential threats. It uses an energy-efficient transmission protocol to reduce the power consumption and enable very long lifetime operation using batteries. Experimental results showed that a 150 meter transmission distance can be achieved with 10 mW total power consumption. The entire sensor package can be built for less than $30/unit at production runs of one thousand units, making it extremely competitive in today's market.

The packaged sensors are mounted on a circuit board containing the detection circuit and microcontroller and the wireless transmitter for data collection. All of this is enclosed in a small, low cost plastic package with an opening for the devices to sample the ambient air. Power is supplied from a wall transformer, with a 9V battery backup that can last 15 days. The current transmission protocol is optimized for low power consumption. The current level of the sensor is monitored every 5 seconds and the receiver is enabled to transmit data after sampling, then turned back off for a very low duty cycle. The entire system is shown in Figure 1.

Sensor with sensor device	Sensor and base station

Computer interface with base station

Figure 1. Photos of sensor system



The Network
A web server was also developed to share the collected sensor data via the Internet. The interface of the server program, shown in Figure 2, illustrates the current level of each sensor on the network. If any of the sensor’s current increases to a level that indicates a potential hydrogen leakage, the alarm is triggered. A program was also developed to receive the sensor data remotely. The remote client is able to acquire a real time log of the system for the past 10 minutes, as well as access the full data log via an ftp client. When an alarm is triggered, the client will able to deactivate the alarm remotely by clicking a button on the interface. The server program for the wireless sensor network could also report a hydrogen leakage emergency through phone lines using the computer’s modem to send a message to cell phones, beepers, etc. Future generations of this program will provide more flexibility, including the capabilities for the client to set alarm levels based on allowed hydrogen concentrations.

Figure 2. Interface of online hydrogen level monitoring (Click to enlarge)

Field tests have been conducted both at University of Florida and at Greenway Ford in Orlando, FL. The outdoor tests at University of Florida have been conducted several times for a period of two weeks, to test a range of possible real world conditions in a more controlled setting. Hydrogen leakage was successfully detected for hydrogen concentrations in a range from 1-100% at the point of the leak and heights ranging from 1-10 ft in an outdoor environment. The setup at Greenway Ford was aimed to test the stability of the sensor hardware and the server software in an operational environment. Several difficulties found during testing have already been improved upon. The sensors have shown good stability for more than 10 months in the outdoor field tests.

In conclusion, a wireless hydrogen sensor network which meets the IEEE 802.15.4 standards has been constructed to transmit data from an arbitrary number of hydrogen sensors to a base station. A user friendly program has been developed to share the data collected by base station to Internet, so that the data can be analyzed and monitored from anywhere with an internet connection. A cell phone alarm has been realized to report any potential hydrogen leakage to responsible personnel. The entire system has been tested for functionality and stability both at the University of Florida and at Greenway Ford in Orlando. Field tests show that the low-power hydrogen sensor can work stably and react quickly to possible hydrogen leakage.

The work at UF is partially supported by ONR (N00014-98-1-02-04, H. B. Dietrich), NSF(CTS-0301178, monitored by Dr. M. Burka and Dr. D. Senich), by NASA Glenn Research Center Grant NAG3-2930 monitored by Mr. Tim Smith, Florida Department of Environmental Protection, U.S. Dept. of Energy (DE-FG26-05R410962 by Jill Stoyshich), and the Office of Technology Licensing at UF under Mr. Karl Zawoy. The authors would like to thank the management and technical team in the Greenway Ford dealership for their technical support.



¹Authors
T. Anderson, H.T. Wang, B.S. Kang, F. Ren (corresponding author: ren@che.ufl.edu) - University of Florida, Department of Chemical Engineering, Gainesville, FL 32611

C. Li, Z.N. Low, J. Lin2 - University of Florida, Department of Electrical and Computer Engineering, Gainesville, FL 32611

S. J. Pearton - University of Florida, Department of Materials Science and Engineering, Gainesville, FL 32611

A. Osinsky, Amir Dabiran, P. Chow - SVT Associates, Eden Prairie, MN 55344

J. Painter - J Painter Consulting LLC, Deltona, FL 32738