Forums

Sensors for monitoring motors and pumps?

Started by Rune Allnor February 1, 2009
Hi folks.

Assume one wants to monitor the mechanical condition a pump
or motor by means of acoustics, and this pump or motor is located
in a room full of other pumps and motors.

What sensors should one use to record the sound?

A naive microphone would likely record the sound from all the
pumps, meaning the acostic signature of the pump under
investigation is corrupted by noise from all the others.

One could of course try and build a sound screen around the
microphone, but it would be a mess or very large to be effective.
Most likely both.

So I'm thinking some sort of accelerometer probe that one
can poke at the pump with, so it measures the vibrations
of the casing and not the sound.

Does anyone know about such probes?

Rune
Am Sun, 01 Feb 2009 04:53:54 -0800 schrieb Rune Allnor:
> > Assume one wants to monitor the mechanical condition a pump or motor by > means of acoustics, and this pump or motor is located in a room full of > other pumps and motors. > > What sensors should one use to record the sound? > > A naive microphone would likely record the sound from all the pumps, > meaning the acostic signature of the pump under investigation is > corrupted by noise from all the others. >
You can put one microphone close to / at the / in the machine, and another one near the machine, but independent from it, perhaps even screened from the machine under observation. BTW: I once worked in a power plant, where we had a pump installed and operating. Even through the earplugs we heard the difference in sound when the pump ran dry. I am astonished at how humans can detect these minute differences (ok, it might haven taken us some unknown time to recognize it).
> One could of course try and build a sound screen around the microphone, > but it would be a mess or very large to be effective. Most likely both. > > So I'm thinking some sort of accelerometer probe that one can poke at > the pump with, so it measures the vibrations of the casing and not the > sound. > > Does anyone know about such probes? >
You might want to look at http://www.vibro-meter.com/ or google around for condition-based maintenance. HTH Martin
On Sun, 1 Feb 2009 04:53:54 -0800 (PST), Rune Allnor <allnor@tele.ntnu.no> wrote:
> Assume one wants to monitor the mechanical condition a pump > or motor by means of acoustics, and this pump or motor is located > in a room full of other pumps and motors. > > What sensors should one use to record the sound? > > A naive microphone would likely record the sound from all the > pumps, meaning the acostic signature of the pump under > investigation is corrupted by noise from all the others. > > One could of course try and build a sound screen around the > microphone, but it would be a mess or very large to be effective. > Most likely both.
How about a "microphone" that was permanently attached to, or at least mechanically coupled to, the motor or pump? Since you would be picking up the vibrations directly, the pump "signal" would be much louder, and you'd have much less interference from other pumps / motors. (In California you might need to worry about seismic vibrations... <grin!>)
> So I'm thinking some sort of accelerometer probe that one > can poke at the pump with, so it measures the vibrations > of the casing and not the sound.
Ah. Are you thinking of one device to test many pumps/motors, or is a dedicated pickup-per-pump more appropriate? If the former, then perhaps a piezo transducer with a short probe attached to touch the pump with, mounted at the end of a well-insulated (sound and electrical) rod. I don't know of a specific manufacturer, but here in the U.S. you can pick up an "engine monitor" that's just a "stethoscope" with a long metal rod (_not_ insulated. Ig.). Hope this helps... Frank McKenney -- "If you think health care is expensive now, wait until you see what it costs when it's free." -- P.J. O'Rourke -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)
On Sun, 1 Feb 2009 04:53:54 -0800 (PST), Rune Allnor
<allnor@tele.ntnu.no> wrote:

>Hi folks. > >Assume one wants to monitor the mechanical condition a pump >or motor by means of acoustics, and this pump or motor is located >in a room full of other pumps and motors. > >What sensors should one use to record the sound? > >A naive microphone would likely record the sound from all the >pumps, meaning the acostic signature of the pump under >investigation is corrupted by noise from all the others. > >One could of course try and build a sound screen around the >microphone, but it would be a mess or very large to be effective. >Most likely both. > >So I'm thinking some sort of accelerometer probe that one >can poke at the pump with, so it measures the vibrations >of the casing and not the sound. > >Does anyone know about such probes? > >Rune
This is a very common application for accelerometers. Sometimes shaft displacement sensors are used also if the rotating machine is large enough to use plain journal bearings rather than rolling element bearings, and sometimes a tachometer is used to allow for source-synchronous analysis (and shaft torsional vibration measurement); the relation of vibration frequency to shaft speed identifies the exact nature of many faults. Small inexpensive machinery is often checked periodically by "poking" accelerometers at particular spots and comparing to past readings. Usually the accelerometers are screwed down to a flat surface permanently installed for the purpose (necessary for good repeatability), but sometimes they really are just poked onto the surface by hand for long enough to get a reading (better than nothing). Big expensive machinery like utility turbines and generators are usually monitored continuosly with alarms set at predetermined levels these days. Interpretation of the machinery noise spectrum can be complex enough that some utilities contract that part out to a remote monitoring service. I haven't done this in the last decade, but look for information from the major accelerometer manufacturers like Kistler and Endevco (the two I have used and remember, not necessarily the best for your application) and possibly look for relevant ads and articles on pump and motor monitoring in back issues of Sound and Vibration magazine: http://www.sandv.com/home.htm Glen
Rune Allnor wrote:
> Hi folks. > > Assume one wants to monitor the mechanical condition a pump > or motor by means of acoustics, and this pump or motor is located > in a room full of other pumps and motors. > > What sensors should one use to record the sound?
A contact microphone. This is a field with a long history.
> A naive microphone would likely record the sound from all the > pumps, meaning the acostic signature of the pump under > investigation is corrupted by noise from all the others. > > One could of course try and build a sound screen around the > microphone, but it would be a mess or very large to be effective. > Most likely both. > > So I'm thinking some sort of accelerometer probe that one > can poke at the pump with, so it measures the vibrations > of the casing and not the sound.
In other words, a contact microphone. To listen, I use a stethoscope or hold a chopstick in my molars and touch the free end to where I want to listen.
> Does anyone know about such probes?
http://www.freepatentsonline.com/5804726.html http://www.wipo.int/pctdb/en/wo.jsp?wo=1997014940 Keyword: acoustic signature analysis. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
On 1 Feb, 15:20, Frnak McKenney <fr...@far.from.the.madding.crowd.com>
wrote:

> Ah. Are you thinking of one device to test many pumps/motors, > or is a dedicated pickup-per-pump more appropriate?
At first I would like one or two sensors to play around with as toys and to get experience. The pumps I know of and where I would get access, would be located along with other pumps. Microphones would record the sound of all of them. Of course, as Glen suggested, for operational use one would likely want to mount one or more accelerometers at each pump for repeatability purposes. Rune
"Rune Allnor" <allnor@tele.ntnu.no> wrote in message
news:f0531099-9f3a-4f7c-887c-b6bfeea2de60@v5g2000prm.googlegroups.com...
> Hi folks. > > Assume one wants to monitor the mechanical condition a pump > or motor by means of acoustics, and this pump or motor is located > in a room full of other pumps and motors. > > What sensors should one use to record the sound?
An engine knock sensor or an accelerometer. There are many. Vladimir Vassilevsky DSP and Mixed Signal Consultant www.abvolt.com
On Feb 2, 1:53&#2013266080;am, Rune Allnor <all...@tele.ntnu.no> wrote:
> Hi folks. > > Assume one wants to monitor the mechanical condition a pump > or motor by means of acoustics, and this pump or motor is located > in a room full of other pumps and motors. > > What sensors should one use to record the sound? > > A naive microphone would likely record the sound from all the > pumps, meaning the acostic signature of the pump under > investigation is corrupted by noise from all the others. > > One could of course try and build a sound screen around the > microphone, but it would be a mess or very large to be effective. > Most likely both. > > So I'm thinking some sort of accelerometer probe that one > can poke at the pump with, so it measures the vibrations > of the casing and not the sound. > > Does anyone know about such probes? > > Rune
Accelerometers.
Rune Allnor wrote:
> Hi folks. > > Assume one wants to monitor the mechanical condition a pump > or motor by means of acoustics, and this pump or motor is located > in a room full of other pumps and motors. > > What sensors should one use to record the sound? > > A naive microphone would likely record the sound from all the > pumps, meaning the acostic signature of the pump under > investigation is corrupted by noise from all the others. > > One could of course try and build a sound screen around the > microphone, but it would be a mess or very large to be effective. > Most likely both. > > So I'm thinking some sort of accelerometer probe that one > can poke at the pump with, so it measures the vibrations > of the casing and not the sound. > > Does anyone know about such probes?
Rune, Once you've decided which accelerometers to use, you also might think about the kind of processing you intend. One method would sample the accelerometer data using a tachometer-based sampler. This way, the data is locked to the machine speed and the harmonics are easier to find. You get a cleaner version of the machine noise this way. Fred
"Fred Marshall" <fmarshallx@remove_the_x.acm.org> wrote in message 
news:ivGdnfWpyumTOhvUnZ2dnUVZ_vCdnZ2d@centurytel.net...
> Rune Allnor wrote: >> Hi folks. >> >> Assume one wants to monitor the mechanical condition a pump >> or motor by means of acoustics, and this pump or motor is located >> in a room full of other pumps and motors. >> >> What sensors should one use to record the sound? >> >> A naive microphone would likely record the sound from all the >> pumps, meaning the acostic signature of the pump under >> investigation is corrupted by noise from all the others. >> >> One could of course try and build a sound screen around the >> microphone, but it would be a mess or very large to be effective. >> Most likely both. >> >> So I'm thinking some sort of accelerometer probe that one >> can poke at the pump with, so it measures the vibrations >> of the casing and not the sound. >> >> Does anyone know about such probes? > > Rune, > > Once you've decided which accelerometers to use, you also might think > about the kind of processing you intend. One method would sample the > accelerometer data using a tachometer-based sampler. This way, the data > is locked to the machine speed and the harmonics are easier to find. You > get a cleaner version of the machine noise this way. > > Fred
Analog Devices' "Analog Dialogue" has an article on using accelerometers as acoustic pickups that may be of interest http://www.analog.com/library/analogdialogue/archives/43-02/mems_microphones.html Best wishes, --Phil Martel