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บริษัท อีควิตี้ เซอรวิสเซส แอนด โซลูชั่นส จํากัด
267/96-97 ถนนสุขุมวิท ต.มาบตาพุด
อ.เมืองระยอง จ.ระยอง 21150
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โทร. 0 2998 7308 โทรสาร 0 2998 7309
อีเมล : esscompany@esspower.com
manorom@esspower.com

Equity Services & Solutions Co., Ltd
267/96-97 Sukhumvit Rd. Maptaphut
Mueng-rayong Rayong 21150
Tel : 0 3860 9200

Fax : 0 3860 9201

Tel : 0 2998 7308

Fax : 0 2998 7309

Email : esscompany@esspower.com

Vibration system sensor-loop calibration
Cooling tower
Plant : Gulf JP CRN
Report

Client: MIT-Power (Thailand) Limited

Date: July 2, 2013
Report No. : RPO-S-13-F-036
By : Manorom Chiewpanich, Equity Services and Solutions Co., Ltd.

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Index
1. Summary
2. Background
3. Measurement data
4. As found and Analysis
5. Recommendation
6. Appendix

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1.

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Summary

Vibration loop verification and loop calibration were made from Bay-3-2-1 respectively.
1.1 Vibration sensor loop has “mild” interference from electrical line that can be
neglected. See Appendix -1
1.2 All three(3) vibration sensors produce accurate signal against the reference exciter at
160 Hz
1.3 At 160 Hz exciting to all three(3) sensors generating vibration 4-20 ma signal loop
accurately, vibration reading from DCS showed accurate overall vibration value
similar to external vibration . See section 3
1.4 Trip point is set at 12,7+0,1 mm/s peak which is equivalent to 9,05+0,04 ma at all
three(3) vibration loops.
Plotted plan
Bay-3

Vibration shaker

Bay-2

Bay-1

Current meter and
vibration analyzer

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2. Background
This report was made to cover the provision of three(3) vibration sensor loop calibration at
cooling tower, plant Gulf JP CRN against customer Work Order No. BC018562 issued by
MIT power( Thailand) Limited.
This task was carried out on June 26, 2013 as per call-off basis, resulting we were not aware
on safety issues according to customer standard.
Moreover, we did not pre-program on vibration measurement recording. Fortunately, two
data records were saved as ;
• Bay-3 when sensor was shaken at 10 Hz during loop verification
• Bay-2 when it was measured during fan was operated after calibration and trip point
setting was finished
Bay-3, signal reading from customer sensor from 10 Hz excited.

Power line interference

Waveform reading in m/s2

Spectrum reading in mm/s peak
at full scale 20 mm/s


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Bay-2 , actual vibration signal at 3 mm/s full scale.

Blads pass frequency

Gear mesh frequency


Structure and windage noise threshold

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3 Measurement data
Customer sensors were excited In-Situ using variable frequency and variable magnitude
shaker.
Current loop was measured by adding local current meter in between.
Voltage output from customer’s sensor that feeds to local controller, it was parallel connected
to external vibration analyzer while sensitivity was set at 10,1 mv/m/s2 ( to meet sensor
output at 100 mv/G )
From our preliminary assessment, we found 4-20 ma output is not accurate at low frequency.
On the other hand, 4-20 ma output is accurate at 100 Hz or higher. But shaking at high
frequency to give the same amplitude at low frequency and further to reach the trip point is
not possible due to the law of energy conservation. We therefore excited the sensors at 160
Hz, varying the magnitude allowing vibration controller to generate the current loop from 4
to 20 ma. Below is calibration loop.

Notice. Signal that excited the vibration sensor is sine wave at single frequency while
vibration from real operation is complex ( See Appendix-2). Customer vibration tool is
simple signal processing for safeguarding propose , while the external signal analyzer is
sophisticate tools for analysis purpose. Resulting customer vibration tool has limited
capability compare to sophisticate vibration analyzer, thus giving low overall vibration
reading.

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4 As found and analysis
Since this task is only calibration and loop verification.
Hereby is to verify ; All three(3) vibration protection loops are functional and trip point are
proper setting to ISO 10816 compliance

As found, vibration switch at bay-1 is not self-reset. To reset, operator must reset at local
reset button.

5 Recommendation
Sensor and loop should be calibrated and verified at lease every 3 years.

6 Appendix
Appendix-1, mild interference from Power line
Appendix-2, Signal characteristic between calibration signal and operation signal

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Appendix -1
Mild 100 Hz power line interference

Power line interference, but it is negligible due to
constant at very low magnitude.

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Appendix-2
Single frequency pseudosoidal wave to excite sensor

Complex signal at operation condition

*** End**

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