Field Measurements

Field measurements provide real-time information on the actual operating conditions of mechanical equipment, piping, and structures, including vibration and stress levels. These data not only aids in diagnosing and resolving issues but also serves as a valuable tool for calibrating and validating analytical models. Furthermore, field measurements can uncover problems that are challenging to predict through analysis alone, such as manufacturing tolerances, installation errors, and equipment aging. By conducting these measurements, early signs of failure can be detected, enabling preventive maintenance before more significant issues arise.

Field Measurement Procedure

Below is a flowchart outlining the procedure for conducting a field measurement.

Field Measurement Instruments

Field measurement instruments are essential tools for conducting on-site measurements. At CCPGE, we utilize the following instruments for accurate data collection:

• Data Analyzers record and process measured data on-site, providing preliminary results with minimal measurement and processing time. CCPGE is equipped with dual-channel mobile analyzers and multi-channel data acquisition (DAQ) systems, enabling both fast and complex interventions.
• Accelerometers measure vibration levels in terms of acceleration (g), velocity, and displacement across a wide frequency range (0.5 Hz to 10 kHz).
• Piezoelectric Pressure Transducers measure pressure fluctuations and capture pulsation characteristics effectively.
• Encoders measure angular displacement during torsional vibration tests.
• Strain Gauges installed on surfaces to directly measure both dynamic and static stress levels.
• Impact Hammers used to deliver controlled impact for modal testing purposes, dynamic properties such as natural frequencies, damping, and mode shape can be determined.

The figure below illustrates the multi-channel vibration measurement system used at CCPGE. This system consists of sensors, an NI data acquisition module, a cDAQ module, and an NI LabVIEW-based signal processing system. Detailed performance data is provided below.

(1) cDAQ 9174, up to 4 I/O modules, 32-bit, 100 KS/s

(2) NI 9234, 24-bit dynamic signal acquisition module

• 4 input channels for simultaneous acquisition of dynamic signals
• IEPE sensor compatible
• 24-bit ADC
• Sampling rate up to 51.2 Ks/s per channel
• Frequency response from DC to 25 kHz (-3 dB)

(3) NI 9215, analog voltage input, up to ±10 V

• 16-bit ADC
• High absolute accuracy of 0.015% of range
• Sampling rate up to 100 kS/s

(4) PXIe-4499, 24-bit, 204.8 kS / s, 4 Gain, TEDS, AC / DC coupled

• 16-channel sampling inputs with sampling rate up to 204.8 kS/s
• ADC with 24-bit resolution and 114 dB dynamic range
• 4 kinds of up to +30 dB gain settings to guarantee the input signal ranging from ± 316 mV to 10 V
• 4 mA IEPE and TEDS configured by software for microphones and accelerometers
• 5 HZ coupled AC analog input
• Synchronization of up to 272 full-bandwidth channels within a PXI Express box

(5) PCB 356A26 Triaxial acceleromter

• Sensitivity (±10%) 50 mV/g
• Measurement range ±100 g pk
• Frequency range (±10%) 1 to 5000 Hz
• Broadband resolution 0.0002 g rms
• Resonant frequency ≥ 25 kHz

(6) TT10K-LP torque telemetry system

• Robust and precise strain measurement
• Digital RF to transmit data signal
• RX10k Receiver with 500 Hz frequency response
• TX10K transmitter with high signal to noise ratio

(7) H20 incremental encoder

• Maximum RPM 10000 RPM
• Cycles per shaft turn 1 to 10000 RPM
• Frequency response 300 kHz

Field Measurement Technics

CCPGE primarily employs the following techniques to conduct field measurements:

• Operating Deflection Shape (ODS): This technique measures relative vibrations during the test and generates a deflection shape by processing the collected data.
• Speed Sweep Measurements: These capture vibration amplitude and phase across the machine system at all operating speeds for variable frequency drive (VFD) applications.
• Motion Amplification Camera: This technology provides an effective vibrational assessment and visualizes the ODS.
• Computational Simulations: These evaluate pulsation levels, mode shapes, and mechanical and torsional vibration levels by integrating analysis with on-site data.

Field Measurement Guidelines

A wide range of field measurement guidelines is available, and CCPGE typically utilizes the following standards:

• ISO 20816: Mechanical Vibration – Measurement and Evaluation of Machine Vibration
• ISO 21940: Mechanical Vibration – Rotor Balancing
• ISO 2041: Mechanical Vibration, Shock, and Condition Monitoring
• ISO 10326: Mechanical Vibration – Laboratory Method for Evaluating Vehicle Seat Vibration
• API 618: Reciprocating Compressors for Petroleum, Chemical, and Gas Industry Services
• API 619: Rotary-Type Positive-Displacement Compressors for Petroleum, Petrochemical, and Natural Gas Industries
• API 676: Positive Displacement Pumps – Rotary
• ASME PTC: Performance Test Codes
• European Forum of Reciprocating Compressor Guidelines

An example of field vibration measurements conducted on eight reciprocating compressor units at a gas storage facility is illustrated below. Each compressor unit features a 6-throw design with 2-stage compression. After operating for 1,625 hours, a total of 17 suction bottle connection bolts were found broken across seven of the compressor units, and the outlet nozzle of the first-stage suction bottle in one unit was cracked due to excessive vibrations. Field measurements were necessary to investigate the root causes of these failures and to implement appropriate resolutions. The compressor units, broken bolts, and cracked suction bottle are depicted in the following figures.

CCPGE conducted field vibration measurements on key components, including the motor, compressor frame, cylinders, suction and discharge bottles, scrubbers, and connected piping. The measurement locations are indicated below. The measured vibration signals were processed, with one example shown here, and integrated with pulsation and mechanical vibration analysis results to identify root causes. Corresponding solutions were proposed, leading to the resolution of the issue.