A case study describing a reliable system for testing generator vibration levels after production in order to verify proper unit design and assembly.
Our test engineers are often called upon to deploy unattended or “black box” data acquisition systems in the field. These systems are deployed on machinery, vehicles, and industrial processes to constantly record strain and vibration data at sample rates between 100 and 100,000 Hz. That adds up to a lot of data to sift through.
In situations where we are trying to identify system operation outliers or damaging events, we utilize the Automated Analytics application in iTestSystem to limit the amount of data searches required. The Automated Analytics application allows users to analyze, build, and send sensor level reports only when specific vibration and strain limits are exceeded. Instead of searching through data files, engineers can easily review the report and download relevant data files from deployed systems for further analysis.
This video demonstrates how to build and send vibration and strain reports using Automated Analytics and other iTestSystem tools and applications.
- Strain Gauge Installation for Field Testing
- General Purpose Accelerometers for Rotating Machinery Vibration Measurements
Choosing an accelerometer for rotating machinery vibration measurements can be a daunting task since there are so many options available. This blog outlines the characteristics you should consider when choosing a piezoelectric single axis accelerometer for general purpose vibration measurements and presents some accelerometers to consider.
Characteristics of a General Purpose Accelerometer
When measuring vibration on rotating equipment such as motors, pumps, and generators, the most common measurement location(s) are on the shaft bearing housing(s) at the shaft centerline. At this location, typical vibration levels perpendicular to the shaft are < 100 g and the frequency range of interest is < 5000 Hz. A general purpose single axis piezoelectric accelerometer with either a 10 mV/g or 100 mV/g sensitivity fits this criteria.
Other characteristics to consider are size, mounting options, cable connections, grounding, and cost. Several mounting options are available. They include magnetic bases, adhesive bases and stud mounts. The mounting option you choose affects the frequency range of your accelerometer measurements. The table below shows typical frequency limits for accelerometer mounting methods.
|Mount Type||Typical Frequency Limit|
5 General Purpose Accelerometers
The table below shows some examples of stud mounted general purpose piezoelectric accelerometers. These accelerometers all have a female 10-32 coaxial / microdot connector. It is important to note that this is not a complete list of accelerometers and there are many options available from each manufacturer. I would encourage you to go to the websites linked in the table and see what’s available.
|Manufacturer||PCB||Dytran||BRÜEL & KJÆR||Endevco||Kistler|
|Model #||353B03||3055D1||4533-B||256HX -10||8702B500-M1|
|Sensitivity||10 mV/g||10 mV/g||9.8 mV/g||10 mV/g||10 mV/g|
|Frequency Range||(±5%) 1 to 7000 Hz||(±5%) 1 to 5000 Hz||(±10%) 0.2 – 12800 Hz||(±10%) 1 to 10000 Hz||(±5%) 1-10000 Hz|
|Temperature Range||-65 to +250 °F||-67 to +250 °F||–67 to +257 °F||-67˚F to +257˚F||-67˚F to +257˚F|
|Height||0.88 in||0.64 in||0.54 in||0.55 in||0.67 in|
|Weight||0.38 oz||0.35 oz||0.3 oz||0.14 oz||0.32 oz|
|Electrical Connector||10-32 Coaxial (side)||10-32 Coaxial (side)||10–32 Coaxial (side)||10–32 Coaxial (top)||10–32 Coaxial (side)|
|Mounting Thread||10-32 Female||10-32 Female||10-32 Female||10-32 Female||10-32 Female|
Our test engineers collect vibration data on rotating machinery using four basic tools. We use a Laptop computer with iTestSystem software to stream accelerometer and rotational/speed pulse sensor data from a National Instruments cDAQ equipped with vibration and voltage input modules. The video above shows how to collect vibration data using iTestSystem and a cDAQ.
Vibration Test Equipment
- Laptop with iTestSystem Software (Download Free Version)
- IEPE Accelerometers (607A60)
- Rotational/Speed Pulse Sensor (SICK WL9L-3P2232)
- NI cDAQ Chassis with Vibration and Voltage Modules (cDAQ-9189, NI-9234, NI-9229)
Vibration measurements are usually derived by analyzing data collected from IEPE accelerometers mounted to the rotating machinery structures and components of interest with magnetic bases or epoxy and a rotational/speed pulse sensor. Typical rotational/speed pulse sensors are magnetic pickups excited by gear teeth and keyways or optical sensors triggered by reflective tape adhered to the rotating machinery.
The most important part of the data collection process is choosing a sample rate. If you choose a sample rate that is too low, the data you have collected is useless. According to the Nyquist Theorem data must be sampled at a rate that is at least 2X the highest frequency you wish to record. 2X the highest frequency is a minimum number. Most test engineers like to sample from 2.5x to 10x higher than the highest frequency they wish to collect.
Typical general vibration measurements are sampled at 2kHz. However, vibration data collected from accelerometers and gear teeth pulses which is used for phase and speed measurements, and bearing fault detection, and torsional vibration determination must be collected at much higher sample rates like 50kHz.
For more information about collecting vibration data, iTestSystem, or test equipment rental, contact Ryan Welker @ (844) 837-8797 x702.
Last week our team successfully and safely installed another Boiler Monitoring System (BMS). This system, a Sootblower Fouling Detection (SFD) system, monitors structural and vibration sensors that quantify the boiler’s response to sootblower operations. The SFD system analyzes the boiler response data and outputs Key Performance Indicators (KPIs) such as fouling level, sootblower efficiency, and sootblower health to automated boiler cleaning systems.
This boiler uses over 50 sootblowers located at different elevations to clean soot build-up from boiler steam tubes. Since the vibration measurement locations are relatively far apart, the SFD system requires a distributed monitoring system consisting of several junction boxes that monitor and process data for groups of sensors. One team of engineers mounted the vibration sensors to the sootblowers and confirmed communication back to a local junction box containing the National Instruments condition monitoring hardware. The other team installed the junction box panels and terminated the sensor cables.
After all the sensor installations and terminations were completed, each sensor’s location and calibration were verified. While the sensor verification was being completed, one engineer worked with the mill IT department and the controls engineer to establish remote connection to the system and confirm communication with the mill’s automated cleaning system.
After commissioning the system and returning to our home base, our engineers are now monitoring the system through a VPN connection and assisting boiler operators with optimizing their cleaning process.
Over the years we have been tasked with identifying the root cause of machine structural failures. In many cases, we can determine the failure mode through strain and vibration testing, order analysis, modal analysis, and operating deflection shape analysis. What tests can you run when the damaging conditions are intermittent and not easily identified?
In these cases, we like to install a cellular networked temporary data acquisition (DAQ) system that can autonomously log vibration and strain data along with machine status data. We have deployed two types of DAQ systems to collect data remotely. An interactive system that includes an industrial PC running our iTestSystem software and National Instruments (NI) Compact DAQ hardware and a headless system that utilizes NI Compact RIO hardware. Our test engineers prefer using the interactive solution for troubleshooting because they can view real-time signal waveforms and collected data files, and then adjust the test parameters accordingly without having to reprogram the hardware.
Figure 1: Headless networked data acquisition system
When potentially damaging events are identified in the vibration and strain data collected by these systems, it is important to know the machine’s operating status. Collecting the machine status information is just as important as collecting the structural data. Many machines transmit these operating variables and operating stages over their network/bus. Recently we have recorded process data from Allen Bradley Control Logix PLCs via Ethernet/IP, mining machine data from a Siemens controller via proprietary TCP/IP protocol, boiler condition data from a DCS via Modbus TCP, machine pressures from PI historian via the UFL connector (TCP), and vehicle speeds and pressure via CAN. Fortunately, we were able to use and adapt LabVIEW communication protocol tools to build applications and addons that allow this network tag data to be collected along with structural data.
Figure 2: Modbus to Shared Variable Tool
After the data collection phase, our engineers perform statistical analysis on the sensor and status channels in all data files and aggregate the results into a database for searchability. To identify the root cause probabilities, you can process the channel statistics data using your favorite correlation algorithm or application. The image below shows an example data set containing related sensor data that was processed using a LabVIEW correlation test tool.
Figure 3: Correlation Test Example vi
Contact Information: For more information about our remote data acquisition service, our LabVIEW development service, or iTestSystem contact:
Mark Yeager – Integrated Test & Measurement (ITM), LLC. Email: email@example.com or Phone: 1.844.TestSys
The FieldDAQ™ FD-11634 sound and vibration input module from National Instruments (NI) can now be used with the latest version of iTestSystem. The FD-11634 is similar to the NI-9234, NI-9232, NI-9231, and NI-9230 cDAQ dynamic input modules and can be used with IEPE type sensors such as accelerometers and microphones. Like the other FieldDAQ™ modules, this module is IP65/IP67 dust and water resistant with an operating temperature range of -40 °C to 85 °C. Our test engineers would use these modules for collecting vibration data on mining and construction equipment, vibration data on rotating machinery within manufacturing facilities and test cells, and acoustic data for measuring equipment noise emissions.
The FieldDAQ™ FD-11634 module has 8 simultaneous sampled, ±1V or ±10 V, 24-bit differential input channels with AC/DC coupling. It has a maximum sample rate of 102.4kS/s and features built in anti-aliasing filters that automatically adjust to the sampling rate.
For advice about using the FieldDAQ™ FD-11634 sound and vibration modules in iTestSystem monitoring applications or with custom cRIO RT and FPGA control applications contact Mark Yeager or Chase Petzinger.
Click Here to view a video showing one of our test engineer collecting data from a submerged FieldDAQ™ module with iTestSystem.
Click Here for more information about iTestSystem.
Over the past few weeks we have been updating our Joint Time Frequency Analysis (JTFA) tool for iTestSystem. In general, the JTFA tool is used to show how the frequency content of a signal changes over time. This tool is particularly useful for analyzing and visualizing vibration and strain data on rotating machinery.
After using the JTFA tool on an internal data analysis project with a colleague, we realized that with a few additions and changes, the tool’s capabilities and processing efficiency could be greatly improved. To achieve this, we added a configurable overall frequency band algorithm for trending frequency bands related to specific machine fault or vibration modes. We also added templates for quickly developing and switching between frequency band signatures and settings. Finally, we added the capability to export the results to a data file for later viewing in TestView Plus or Excel.
Category III Vibration Analysts are qualified to establish, direct, and\or perform programs for condition monitoring and diagnostics of machines including spectral, waveform, and orbit analysis. Category III certified Vibration Analysts are qualified to perform minor corrective actions involving operating deflection shapes, single-plane balancing, and diagnostic testing.
ITM | Integrated Test + Measurement
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Milford, OH 45150
Email: ITM Sales
ITM provides software development, structural and mechanical testing services, industrial monitoring, strain gauging, and data analysis solutions to clients on six continents. ITM is a recognized National Instruments Gold Alliance Partner.