Case Study: Fan Acceptance Testing

Thank you to Brian Franks at JetTech Mechanical LLC for providing the data for this case study

Download the printer-friendly Fan Acceptance Testing Case Study .pdf 

Introduction
JetTech Mechanical LLC was commissioned to perform acceptance testing for a 12-fan assembly unit. JetTech set up a temporary monitoring system using magnet-mounted CTC TREA330 Triaxial Sensors.

They performed acceptance testing on four fans at a time, with sensor cabling run back from each set of four fans to the CTC TSB1000 Series Triaxial Switch Box. 252 readings were taken over two hours of fan run time. Data was collected at each point at 20, 35, 40, 45, 50, 55 and 60 Hz.

Acceptance Criteria Used
ISO14692_2003

Machine Overview
The fan is classified as BV-3 because of motor size. The fan is also classified as rigid mounting because the frame/mount for the motors did not have a natural fundamental frequency lower than the lowest operating frequency.

Hardware Used
JetTech selected triaxial accelerometers for this project due to the number of vibration points requiring testing. Triaxial accelerometers allowed JetTech to collect data from hundreds of data points on 12 fans within a two-hour window, whereas single-axis sensors would significantly extend the time required. As a result, JetTech selected CTC TREA330 Series Triaxial Accelerometers due to their premium frequency response capabilities, as well as CTC mounting magnets and CTC data collector connector.

TREA330
Premium miniature industrial triaxial accelerometer, side exit 4 pin mini-MIL connector, follows Cartesian phase coordinate system, 100 mV/g, ±5%

MH114-3T
Multi-purpose two-rail magnet mounting base with 1/4-28 blind tapped hole and triaxial alignment notch, 50 lbs. (23 kg) pull strength, 1.39 in. (35.31 mm) OD, 0.85 in. (21.59 mm) height

CB105-J4C-020-F3D
Four-conductor shielded cable with black polyurethane jacket, 0.25 in. (6.4 mm) OD, 250 °F (121 °C) Maximum Temperature; Connector 1: four-socket mini-MIL connector with rubber bending strain relief, polyurethane molded; Connector 2: three-channel BNC plug connector, polyurethane molded; 20 ft. overall length

BetaVib VibWorks Data Analyzer

photographs of a CTC TREA330 triaxial accelerometer magnet mounted to an industrial fan unit connected via CTC cable and connector cordset to a BetaVib VibWorks Data Collector

Analysis
The following table shows the acceptance amplitudes permissible at any single axis. For this report, we are using inches/sec PEAK value of 0.346/s PEAK.

actual photo of sensors and positions

Impact Test Results - Overview
JetTech Mechanical performed calibrated impact testing on all 12 axis points in the above photo (M1 Motor H-V-A; F1 Mid-Frame H-V-A; F2 Base-Frame H-V-A and FV3 Wall H-V-A).

Motor Horizontal
We see a clear 63.12 Hz fundamental critical frequency with the confirming 90° phase shift:

Motor Vertical 
We see a clear 36 Hz critical frequency with the confirming 90° phase shift:

Motor Axial
We see a clear 15.75 Hz critical frequency with the confirming 90° phase shift:

Frame Midpoint Horizontal
No appreciable critical frequencies in this axis in the operating range of 17 - 34.5 Hz:

Frame Midpoint Vertical
No appreciable critical frequencies in this axis in the operating range of 17 - 34.5 Hz:

Frame Midpoint Axial
No appreciable critical frequencies in this axis in the operating range of 17 - 34.5 Hz:

Frame Base Horizontal
No appreciable critical frequencies in this axis in the operating range of 17 - 34.5 Hz:

Frame Base Vertical 
No appreciable critical frequencies in this axis in the operating range of 17 - 34.5 Hz:

Frame Base Axial
No appreciable critical frequencies in this axis in the operating range of 17 - 34.5 Hz:

Wall Horizontal
We see a clear 5.35 Hz critical frequency with the confirming 90° phase shift:

Wall Vertical
We see a clear 9.75 Hz critical frequency with the confirming 90° phase shift:

Wall Axial
We see a clear fundamental critical failure frequency of 15 Hz with the confirming 90° phase shift: