guidance for mounting 4-20ma sensors on fans

8/3/2019 Guidance for Mounting 4-20mA Sensors on Fans

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Guidance for mounting 4-20 mA vibration sensors on fans This article provides guidance to determine the number and location of 4-20 mA loop powered sensors (LPS) which produce a reliable vibrationmonitoring system to protect fans. LPS interface directly with a plantProgrammable Logic Controller or Distributed Control System to provide acost-effective predictive maintenance solution.

Measurement directions

Fan monitoring typically utilizes triaxialmeasurements, taken in the vertical ( V),horizontal ( H), and axial ( A) directions. Thevertical and horizontal measurements are meantto be perpendicular to the rotating shaft. Axial ismeant to be taken in the same direction as theshaft.

H

H

V

V

A

A

When mounting piezoelectric-based vibrationsensors, the base of the sensor is mountedtoward the shaft or bearing. Horizontal mounting

can be done on either side of the bearing.Vertically mounted sensors can either be aboveor below the shaft; however it is normally moreconvenient to mount them on the top of thebearing.

General measurement

V

HA

V

AH

On belt-driven equipment the vertical andhorizontal are sometimes rotated slightly so as toalign the measurement with the direction of theshafts centerlines. In this case the horizontal isperpendicular to the shaft, but aligned to the

opposite shaft.


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IB OBOBFan

Motor

FanOB IB

Motor

Fan location designations

OB

Measurement locationsMachinery vibration analysts have developedsome standard reference terminology forequipment locations. Monitoring points are usuallydesignated as inboard ( IB) or outboard ( OB ).Outboard is the side of the fan or motor away fromthe coupling or belt sheave. Inboard is the end ofthe fan shaft closest to the coupling or beltsheave.

Further point identification is also whether thepoint is on the fan ( F) or motor ( M). i.e.- inboardfan ( IBF) or outboard motor ( OBM).

Belt driven equipment has a slightly differentorientation when considering the horizontaldirection. The horizontal direction for the shaftends with the belt sheaves is directed between theshafts. In other words, the horizontal for one shaftis pointed at the other shaft.

Measurement preferenceWhen viewed as a whole system, a fan has a maximum number of twelve (12)measurement positions. Each of four (4) typical locations has a possible three (3)measurement axes (vertical, horizontal, and axial).

Vibration measurements made using a portable data collector (analyzer) usually will betaken at all twelve (12) positions. Because the data is acquired at intervals of a month,or more, it is relatively simple to just take data from all positions while the vibrationtechnician is at the fan. This provides the maximum amount of data for analysis in theminimum of time.

When it comes to mounting accelerometers for predictive maintenance programs aquestion often asked is, "Do I really need to install accelerometers in all three axes ateach bearing location?" The answer is, generally, "No." Even ISO 10816 , a documentthat sets the industry standard for vibration monitoring, allows that only one or twomeasurements at a bearing position are necessary for operational needs.

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Typical recommended sensor locations

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Recommended Alternate

Belt-driven fan side

IBF-H OBF-A

OBF-H

IBM-H

OBM-H

Direct-drive simply supported

IBF-H

OBF-H

Alternate alocatio

xialn:IBF-A

IBF-H

OBM-H

IBM-H

IBM-A

Direct-drive overhung

OBF-A or IBF-A

IBM-A

IBM-H

OBM-H

Alternate axial locations

OBF-H

Belt-driven fan end-shaft

IBF-HOBF-A

OBF-H

IBM-HIBM-H


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Wilcoxons LPS SeriesWilcoxon Research makes an extensive line of 4-20 mA loop powered sensors to meetthe needs of virtually every application. LPS are ordered with a selectable full scalein terms of acceleration or velocity, output in terms of RMS, equivalent peak, or truepeak, and dual output of dynamic data is also available in acceleration or velocity.

Standard products include environmental protections such as side exit connectors,integral cables, intrinsically safe sensors, and explosion proof housing. Contact aWilcoxon customer sales and service representative to learn more about LPSsolutions for every predictive maintenance program.

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guidance for mounting 4-20ma sensors on fans

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