Short-Range Radio Transmission Of Sensor Data
Authors: Chien L.C. 
Published: October 2008

A radio-frequency (RF) data acquisition system collects and displays drilling data while eliminating the problems of hard wiring. In the past, data for safe, efficient drilling (i.e., pump rate, pressure, flow rate, rotary speed, torque, hook load, block position and mud pit volume) was measured by sensors hard-wired to a central readout or operations area. The new system has independent RF transponders at each sensor location, powered by batteries with life expectancies of more than three months. Expensive and troublesome cable-tray or conduit installations, environmental or mechanical damage to bundled instrumentation cable and limited flexibility of sensor location and portability are eliminated. Low-powered RF system sensors are intrinsically safe.

The data in each sensor of the RF data acquisition system is sampled periodically by a central data receiver. The system is also capable of remote readouts. The central receiver is microprocessor-based for intelligent data processing. Rapid sampling of a specific parameter is also possible when needed. A total of 256 data channels can be sampled, with a range of about 1000 ft in a drilling-rig environment. Field tests comparing the RF system with a hard-wired system demonstrate its practicality, accuracy, reliability, freedom from interference, and physical attributes.

INTRODUCTION

Well site data acquisition systems collect and analyze data essential for safe and efficient drilling. A sensor, processor/readout, and interface comprise an electrical system capable of measuring pump rate, pressure, flow rate, rotary speed, rotary torque, hook load, block position and mud volume. The interface is created by hardwiring a multi-conductor cable consisting of power, ground, signal, signal ground and shield between the sensors and the processor/readout. A low-power radio-frequency interface will eliminate many of the problems inherent to a hardwired link.

Installation and operational problems from faulty or damaged wiring result in substantially increased operating costs and marginal quality data. The majority of time installing a multi-sensor system on location is spent stringing cables, tracing wiring, and checking poor field connections, crossed wires or shorts in the cables. Mechanical abuse arising from heavy machinery coming into contact with the cable or from excessive movement can cause a cable to break or short during operation. Water intrusion, salt atmospheres, poor field crimp connections or bad grounds frequently cause poor signal quality. Due to inconvenience or difficulty, many of these types of operational problems are never fully corrected. Often the best solution is to simply restring the cable.

Armored instrumentation cables, conduit and specialized cable trays solve some of the problems. At many offshore and other hazardous locations (because of the presence of explosive vapors) the conductors have been enclosed with conduit, and the sensors and junction boxes have been explosion-proofed. However, this is expensive, time-consuming and limits flexibility in placing the sensors and readouts.