Previous in Forum: Wireless Remote Pressure Gauge / Sensor   Next in Forum: Functional Test -mA Values to be Sent Using Communicator to Test SIF Function
Close
Close
Close
12 comments
Anonymous Poster #1

Vibration Gap Voltage

02/21/2019 10:43 AM

What is the difference if axial and radial vibration gap voltage is set to -10 VDC or -9 VDC? This 3300/3500 series bently nevada. Many thanks for your answers

Reply
Interested in this discussion?
You can "subscribe" to this discussion to be notified of new comments.
Click on the Subscribe menu at the top of the page.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 29986
Good Answers: 1673
#1

Re: Vibration Gap Voltage

02/21/2019 11:39 AM
__________________
Break a sweat everyday doing something you enjoy
Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 14885
Good Answers: 916
#2

Re: Vibration Gap Voltage

02/21/2019 12:01 PM

The difference is one volt.

{Somebody had to say it.}

__________________
"Don't disturb my circles." translation of Archimedes last words
Reply Score 1 for Good Answer
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 29986
Good Answers: 1673
#4
In reply to #2

Re: Vibration Gap Voltage

02/21/2019 1:13 PM

Thank you for that brief sojourn into the exciting and often confusing world of mathematics....

Stay tuned for more wizardry....

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 29966
Good Answers: 809
#3

Re: Vibration Gap Voltage

02/21/2019 1:09 PM
__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Reply
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 8762
Good Answers: 999
#5

Re: Vibration Gap Voltage

02/21/2019 9:38 PM

The probe generates an RF magnetic field which induces Eddy currents in the conducting shaft. The receive part of the probe senses the generated signal and the signal from the induced Eddy currents. These Eddy currents partially cancel out the probe signal and the result is that the closer the probe is to the surface, the more the signal is cancelled.

This signal is converted to DC and the value is about linearly related to the distance of the gap within the design range of the probe. The gap is set so that the gap voltage is about half the linear range so that there will be the maximum amount of leeway in either direction.

Bottom line: You want the gap to be set about in the middle of the range but it is not critical.

This document explains how it works.

http://www.geocities.ws/alfiefernandes/bentlynevada.htm

Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 29986
Good Answers: 1673
#6
In reply to #5

Re: Vibration Gap Voltage

02/21/2019 10:41 PM

So as the number goes up the sensitivity is decreased? ....or is the sensitivity increased? ....or is it nether, it just properly tunes the probe output to the sensor? ...or is it (D. none of the above?

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru

Join Date: Jul 2016
Posts: 1000
Good Answers: 67
#7
In reply to #6

Re: Vibration Gap Voltage

02/21/2019 11:15 PM

Lower voltage gives you a 10% sensitivity reduction, not that you would likely ever notice the difference outside of a lab....

Reply
Guru

Join Date: Apr 2010
Location: About 4000 miles from the center of the earth (+/-100 mi)
Posts: 8762
Good Answers: 999
#9
In reply to #6

Re: Vibration Gap Voltage

02/22/2019 10:14 AM

Here's what I understand...

When the probe is close to a conducting surface, a low negative is output. As the probe is moved outward, the output voltage becomes more negative. As the object vibrates or moves in and out, the voltage waveform traces out the position of the object with respect to the stationary probe.

The initial position of the probe is adjusted by measuring the output voltage. You would want to set the probe position mid range (~-10 volts) to allow measurements of the object position +/- from the initial position.

http://www.geocities.ws/alfiefernandes/bentlynevada.htm

Here is an answer provided on the AMP forum:

https://www.maintenance.org/topic/prox-probe-set-up-how-to

prox probe set up...How to?

<Question>

"Hullo.

Ive been given the job to adjust some bentley nevada probes on a turbine. I've never seen one of these critters let alone adjusted any. I dont even know if ive called them by the right name. A tiny bit of info I've gleaned is that a multi meter is involved in the process. If anyone here can't explain the procedure and convince me its a straight forward job I'm going to decline the job..."

<Answer>

"...If they are Bently probes you should be able to connect a voltmeter across the signal and common terminals of the proximitor to measure direct current voltage, not AC. Make certain you have a "matched" system; the probe, proximitor, and extension cable have to be very specific items to work properly. An incorrect extension cable, say a 5 meter in a 9 meter system, will yield an incorrectly gapped probe and invalid vibration readings as well.
The COM (typically black) terminal of the voltmeter when connected to the COM terminal of the proximitor will yield a negative voltage. There is quite an allowable range of voltages so you don't need to shot for everything being the same. Again, if Bently, check the voltage across the power and COM terminals at the proximitor. If -18 vDC then shoot for a final gapped voltage around -7 to -8 volts. If -24 vDC (more typical these days) then shoot for something around -10 to -11 volts. As the voltage goes more positive, -10 vDC to -8 vDC say, you are moving closer to the shaft. The scale factor is 200 mV/mil, so in moving from the -10 vDC to -8 vDC you have changed it by 2 volts which is equivalent to 10 mils closer. It helps to know the threads per inch of the adjustment you are making, as you can relate a 1/4 turn to a certain voltage change...."

Reply Score 1 for Good Answer
Guru
Engineering Fields - Mechanical Engineering - New Member Hobbies - CNC - New Member

Join Date: Aug 2006
Location: Western Australia
Posts: 751
Good Answers: 58
#8

Re: Vibration Gap Voltage

02/22/2019 7:20 AM

No difference that matters, as long as you know the axial position of your shaft at that voltage.

__________________
If you can't explain it simply, you don't understand it well enough. (A.E.)
Reply
Active Contributor

Join Date: Jan 2016
Posts: 16
Good Answers: 1
#10

Re: Vibration Gap Voltage

02/22/2019 4:08 PM

Most of the previous posts are 100% right. The proximeter is the I/O device in the junction box. For all the probe applications, the target gap is to always stay in the linear range and to avoid the end ranges, where the readings become garbage. For vibration, we look at the peak to peak variation and not the actual DC voltage. For an axial probe, we are keen to relate the gap to where the shaft is (differential expansion or thrust wear or ...).

Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 29986
Good Answers: 1673
#11

Re: Vibration Gap Voltage

02/22/2019 6:51 PM

__________________
Break a sweat everyday doing something you enjoy
Reply
Guru

Join Date: Dec 2010
Posts: 1619
Good Answers: 111
#12

Re: Vibration Gap Voltage

03/01/2019 9:25 AM

The probe-proximitor is calibrated for a standard steel. While you can set them up on a target of your actual material, this is rarely necessary, but volts change per mm & linear range can vary significantly with material. So linear range & "middle of range volts" can vary. If maximum vibration causes 1 volt peak-peak, then the static voltage is not critical.

Really, you should set the gap with feeler gauges to a value calculated to allow for expansion & eccentricity, but often the range of the probe is such that static gap set by volts is plenty enough to cover variations. You do not want to knock the end of the probe off at working clearances.

You can calibrate on your specific shaft material by moving the probe out by a known distance. You might find this has already been allowed, because the settings schedule [or AC injection test] has a different "gain" from probe volts to vibration amplitude than you would expect from standard sensitivity.

Axial probes can have a really big working range. Machinery often has a significant end float & 1 volt difference compared to radial may just mean axial position at the last machinery stop was different to the set-up position with "-10 volts".

B-N have very good application notes & manuals, read them before adjusting anything!

Reply Score 1 for Good Answer
Reply to Forum Thread 12 comments
Interested in this discussion?
You can "subscribe" to this discussion to be notified of new comments.
Click on the Subscribe menu at the top of the page.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

67model (1); Power Prof (1); PWSlack (1); redfred (1); Rixter (2); rwilliams (1); SolarEagle (4); The Prof (1)

Previous in Forum: Wireless Remote Pressure Gauge / Sensor   Next in Forum: Functional Test -mA Values to be Sent Using Communicator to Test SIF Function

Advertisement