Wireless Sensor System Detects Mechanical Equipment Failures
When an Oil & Gas company began gathering data on mechanical failures in field equipment, they analyzed the expense to repair or replace damaged equipment, and realized that an automated monitoring system would largely reduce repair and maintenance costs. Though the field equipment was visually inspected periodically, it was not often enough to prevent damage. The company envisioned a solution that would employ sensors to detect mechanical failures, but they had no experience in developing an application-specific wireless sensor system that would send equipment status to a central SCADA system. The company engaged Stilwell Baker to design and manufacture the new wireless sensor system.
Stilwell Baker held discovery meetings with the customer to clearly understand the issues facing them in the field and their needs for a new system. Based on the client's well-defined product requirements, Stilwell Baker provided a formal product specification and an estimate for completion of the system architecture and detailed design. After client approval, Stilwell Baker began development of a remote sensor and base module for communication with the existing SCADA system.
The remote sensor module is battery-powered and communicates wirelessly, enabling simple, flexible, and inexpensive installation. The battery size and type are matched to the specific needs of the application, in terms of battery life, rechargeable vs. replaceable batteries, and environmental constraints. The sensor module's power usage is optimized via firmware in the embedded microcontroller, making use of extreme low-power sleep modes. Sub-circuits in the module can be turned on or off as needed to minimize power usage.
Wireless communication is provided with hardware and firmware using the Microchip-proprietary radio protocol called MiWi™, which is based on the IEEE 802.15.4 standard for wireless personal area networks (WPANs). As the Microchip website says, "The MiWi Development Environment is optimized for low-power, low data rate, cost sensitive applications. It also offers a smaller footprint relative to the open standard based ZigBee® compliant protocol stack.” MiWi works on the same 2.4GHz band as ZigBee, but the full inter-operability provided by ZigBee was not required in this sensor system.
Separating signal from noise became an issue since a magnetic sensor is used to measure rotation through the earth’s magnetic field though there is much unrelated change in magnetic field near the sensor. The magnetic field varied in every equipment installation, and can vary at a given installation if the equipment near the sensor is changed over time. To accommodate these variables the firmware algorithm had to be adaptive: able to determine the required signal from the noisy magnetic field measurements.
The engineering team was able to minimize product development time due to off-the-shelf parts, the MiWi development kit, reference designs, software stack, and existing FCC certification. Stilwell Baker produced prototypes for lab testing and client field trials, and manufactures production quantities of the finished system.