The term data acquisition means to measure, digitize, and record values of physical parameters from a system. Or, from an oilfield point of view, it means to record the values of various sensors on a computer. The oldest form of data acquisition is considered to be a pen chart recorder.
Chart Recorders: The earliest oilfield instrumentation used mechanical chart recorders with ink pens drawing on moving paper charts. These analog devices provided a visual record of pressure, temperature, or other parameters over time. While simple and reliable, chart recorders offered limited accuracy, no digital storage, and required manual interpretation of trends. Strip chart recorders are still occasionally used for backup or critical safety monitoring.
Analog Data Loggers: Magnetic tape recorders captured analog signals for later playback and analysis. These systems allowed multichannel recording but required complex playback equipment and offered limited data retrieval capabilities. Tape degradation and calibration drift were ongoing challenges.
Early Digital Systems: The 1970s and 1980s saw introduction of microprocessor-based data acquisition systems. These systems digitized analog sensor signals using analog-to-digital converters (ADCs) and stored data on magnetic tape or floppy disks. Real-time display on CRT monitors improved operational visibility but data storage capacity was limited.
Modern PC-Based Systems: Current data acquisition systems like the Rapidlogger combine powerful embedded computers, high-resolution ADCs, solid-state storage, and network connectivity. Real-time data visualization, automated reporting, cloud storage, and remote monitoring capabilities provide unprecedented operational insight and decision support.
Sensors and Transducers: Convert physical parameters (pressure, temperature, flow, load) into electrical signals. Sensor selection determines measurement accuracy, response time, and environmental suitability. Proper sensor installation and calibration are critical for data quality.
Signal Conditioning: Amplifies, filters, and conditions sensor signals before digitization. Signal conditioning includes:
• Amplification of low-level signals (millivolt strain gage outputs)
• Filtering to remove electrical noise and interference
• Excitation voltage for powered sensors (load cells, RTDs)
• Isolation to prevent ground loops and protect against voltage spikes
• Linearization for non-linear sensor outputs (thermocouples)
Analog-to-Digital Conversion: ADCs convert continuous analog signals to discrete digital values. Key ADC specifications include:
• Resolution: Number of bits (12-bit = 4,096 levels, 16-bit = 65,536 levels, 24-bit = 16.8 million levels)
• Sampling rate: Measurements per second per channel (1 Hz to 100 kHz typical)
• Accuracy: Specified as percentage of full scale or reading
• Input range: ±10V, ±5V, 0-20mA, etc.
Higher resolution and accuracy provide finer measurement discrimination and better signal-to-noise ratio.
FPGA-Based Signal Processing: Advanced data acquisition systems like the Rapidlogger incorporate Field Programmable Gate Arrays (FPGAs) for high-speed, real-time signal processing. FPGAs are programmable integrated circuits that provide parallel processing capabilities far exceeding traditional microprocessors. Key advantages of FPGA-based systems include:
• Ultra-fast data processing: FPGAs handle multiple channels simultaneously with microsecond response times
• Deterministic timing: Precise, jitter-free sampling intervals critical for accurate time-domain analysis
• Hardware-based filtering: Digital filters implemented in FPGA hardware provide superior noise rejection
• Pulse counting and frequency measurement: High-speed counters handle pump stroke sensors and turbine flow meters without missing counts
• Real-time calculations: Complex mathematical operations (FFT, filtering, totalization) execute in hardware without CPU overhead
• Scalability: FPGA architecture easily scales to support 100+ simultaneous input channels
• Reliability: Dedicated hardware logic is more robust than software-based processing in harsh oilfield environments
The Rapidlogger System utilizes FPGA technology to ensure accurate, reliable data acquisition even under demanding conditions with high channel counts and fast sampling rates.
Data Processing and Storage: Embedded computers or industrial PCs process digitized data, apply calibration factors, calculate derived parameters (rates, totals, averages), and store results. The FPGA pre-processes raw sensor data before passing it to the CPU, reducing computational load and enabling faster system response. Modern systems use solid-state drives (SSDs) for reliable long-term storage. Cloud synchronization provides off-site backup and accessibility.
Display and User Interface: Touchscreen HMIs (Human-Machine Interfaces) provide real-time data visualization with trend graphs, digital indicators, alarms, and customizable dashboards. Mobile device apps extend monitoring capabilities to tablets and smartphones.
Sampling Rate: Determines how frequently each channel is measured. Nyquist theorem requires sampling at least 2x the highest frequency component of interest. Typical oilfield applications:
• Slow trends (tank levels, mud density): 0.1 - 1 Hz
• Process control (pressure, flow): 1 - 10 Hz
• Pump monitoring (stroke counting, vibration): 10 - 100 Hz
• Acoustic/vibration analysis: 1 kHz - 100 kHz
Channel Count: Modern systems support 8 to 128+ simultaneous input channels. Channel types include:
• Analog voltage inputs (±10V, ±5V, 0-10V)
• Analog current inputs (4-20 mA, 0-20 mA)
• Thermocouple inputs (Type K, J, T, E)
• RTD inputs (Pt100, Pt1000)
• Strain gage/bridge inputs (mV/V)
• Digital/pulse inputs (frequency, totalizer)
• Serial/network inputs (Modbus, HART, OPC)
Data Storage Capacity: SSDs provide 32 GB to 1 TB storage, enabling weeks to months of continuous high-resolution data logging. Automatic data rollover or archiving prevents storage overflow.
Environmental Ratings: Industrial data acquisition systems must operate in harsh oilfield conditions:
• Operating temperature: -40°F to +140°F (-40°C to +60°C)
• Humidity: 5% to 95% RH non-condensing
• Vibration: 2-5 G continuous per MIL-STD-810
• Shock: 30-50 G peak
• Ingress protection: IP65 or NEMA 4X for outdoor installations
Hydraulic Fracturing: Monitor and record treating pressure, pump rates, proppant concentration, slurry density, and surface equipment parameters. Data acquisition provides real-time job monitoring, automatic stage sequencing, quality assurance documentation, and post-job analysis. Typical systems record 40-80 channels at 1-10 Hz sampling rates.
Cementing Operations: Track pump rates, densities, pressures, and volumes during cement placement. Automated cement heads use data acquisition for density control and additive injection. Job reports document cement placement quality and regulatory compliance.
Drilling Operations: Measure weight on bit, torque, RPM, mud properties, hookload, and downhole parameters. Real-time data enables geosteering, drilling optimization, and early detection of problems (kicks, lost circulation, stuck pipe). Integration with MWD/LWD provides comprehensive drilling intelligence.
Well Testing and Production: Monitor separator pressures, temperatures, flow rates, and fluid levels. Data acquisition calculates production rates, gas-oil ratios, water cuts, and equipment performance. Long-term trend analysis identifies decline curves and optimization opportunities.
Wireline and Coiled Tubing: Record depth, tension, pump pressure, and downhole tool parameters. Real-time monitoring ensures safe operations and optimal tool performance. Data logging documents services for client reporting and liability protection.
System Location: Install data acquisition units in climate-controlled enclosures when possible. Protect from direct sunlight, rain, mud, and excessive vibration. Provide adequate ventilation or cooling for electronics. Mount securely with vibration dampening if required.
Power Supply: Use clean, regulated power sources. Install line conditioning or UPS (uninterruptible power supply) to protect against voltage spikes and power interruptions. Verify voltage and frequency match equipment specifications. Provide separate grounds for power and signal to prevent ground loops.
Wiring and Cable Management: Use appropriate cable types for each signal:
• Shielded twisted pair for low-level analog signals
• Multi-conductor shielded cable for sensor groups
• Armored cable for mechanical protection in harsh areas
Separate sensor cables from AC power lines by minimum 12 inches. Ground shields at one end only to prevent ground loops. Label all cables clearly for maintenance.
Calibration and Verification: Perform initial system calibration by applying known inputs and verifying readings. Document calibration factors, sensor ranges, and engineering units. Verify end-to-end accuracy from sensor through display. Establish periodic calibration schedule (quarterly or annually depending on application criticality).
Software Configuration: Configure channel assignments, alarm limits, trending, and reporting. Set up data archiving and backup schedules. Configure network settings for remote access. Create standardized screen layouts and reports for operational consistency.
IEEE 1451: Smart transducer interface standards for network-capable sensors and actuators. Defines communication protocols and metadata for plug-and-play operation.
IEC 61131-3: Programming languages for programmable logic controllers (PLCs). Many data acquisition systems support ladder logic, structured text, and function block programming for custom control.
OPC UA (IEC 62541): Open Platform Communications Unified Architecture provides standardized industrial automation communication. Enables data exchange between data acquisition systems, PLCs, SCADA, and enterprise systems.
NIST Traceability: Calibration standards and reference instruments must be traceable to NIST (National Institute of Standards and Technology) or equivalent international standards organizations. Maintain calibration certificates and uncertainty budgets.
API Recommended Practices: Various API standards specify data acquisition requirements for specific operations:
• API RP 10B-2: Cement testing and monitoring
• API RP 19D: Hydraulic fracturing operations
• API RP 13D: Drilling fluids testing
Electrical Safety: Data acquisition systems in hazardous locations must comply with:
• NEC Articles 500-516 (Hazardous Locations)
• ISA 12.00.01 (Intrinsically Safe Systems)
• ATEX 2014/34/EU (European explosive atmospheres)
• IECEx Scheme (International explosive atmospheres)
Cybersecurity: Industrial data acquisition systems connected to networks must implement cybersecurity measures per IEC 62443 and NIST Cybersecurity Framework. Use encrypted communications, strong authentication, network segmentation, and regular security updates.
Data Integrity: For regulatory compliance, implement 21 CFR Part 11 (electronic records and signatures) or ISO 13485 requirements. Ensure data is attributable, legible, contemporaneous, original, and accurate (ALCOA principles). Use audit trails and access controls.
