Vibration Monitor (Hyde, Wanttaja?)

Strangely enough, that is what I *DID* for a living when Spectral Dynamics
was the industry leader in machinery diagnostics. Unfortunately, my job was
the circuit design, not the diagnostics itself, so all I concerned myself
with was the black box that took a defined input and produced a defined
output. There are times I wish that I had transferred to the applications
department. They were the ones that seemed to have the most fun (and the
most three martini Friday lunches).


Jim


"

Stangely enough, this is what I do for a living. No kidding.
I am an engineer at Bently Nevada, Corp, the industry leader in machinery
diagnostics.

"RST Engineering" wrote in message
...
Strangely enough, that is what I *DID* for a living when Spectral Dynamics
was the industry leader in machinery diagnostics. Unfortunately, my job
was the circuit design, not the diagnostics itself, so all I concerned
myself with was the black box that took a defined input and produced a
defined output. There are times I wish that I had transferred to the
applications department. They were the ones that seemed to have the most
fun (and the most three martini Friday lunches).


Jim



LOL.
I've been an engineer designing in the dark many times.
Fortunately at Bently, there is a large effort to train engineers in
diagnostics.
Then we can use personal experience in addition to requirements documents
when designing a new product.
Or, at least, we can determine if requirements make sense!

Adam

Understood. What I started out to do (and still plan on doing) is to have a
device that will stay permanently mounted to the engine that can be
calibrated (adjusted, signed, pick a verb) when the engine is known to be
good and light a "your engine is about to come apart" lamp at the
appropriate time.

What this group seems to be leaning toward is a lab quality device that will
allow for sophisticated diagnostics. That ain't the thrust of my Kitplanes
columns. KISS and BURP.

Jim

"RST Engineering" wrote in message
...
Understood. What I started out to do (and still plan on doing) is to have
a device that will stay permanently mounted to the engine that can be
calibrated (adjusted, signed, pick a verb) when the engine is known to be
good and light a "your engine is about to come apart" lamp at the
appropriate time.

What this group seems to be leaning toward is a lab quality device that
will allow for sophisticated diagnostics. That ain't the thrust of my
Kitplanes columns. KISS and BURP.

Jim


As is tradition, we tend to get off topic ;-)
I think you can accomplish this using the methods discussed.
Mount 2 proximity probes 90 degrees apart.
Calibrate the readings for normal low vibrations (be sure to account for any
nonlinearities in the probe).
Design the circuit to trip the buzzer/lamp when the vibration exceeds the
normal level.
You may need some analog circuitry to help (gain, etc).
But you don't need to get much fancier than that.

Adam

Proximity probes? Or accelerometers?

I understand about the analog circuitry and actually plan on making a five
or six channel filter at each of the possible resonance points relative to
the fundamental ... and then strobing the filters to light a "normal",
"low", "high" lamp for each channel.

Jim




As is tradition, we tend to get off topic ;-)
I think you can accomplish this using the methods discussed.
Mount 2 proximity probes 90 degrees apart.
Calibrate the readings for normal low vibrations (be sure to account for
any nonlinearities in the probe).
Design the circuit to trip the buzzer/lamp when the vibration exceeds the
normal level.
You may need some analog circuitry to help (gain, etc).
But you don't need to get much fancier than that.

Adam

I would use proximity probes if you are primarily going to measure
vibration.
They are also the best choice if you are going to notch the shaft and do
phase measurment.
I'm not sure about other venders' prox probes, but the one's I'm used to
have a linear range.
The phase measurment can be gained so that it rails one way when over the
notch and rails the other way when not, so you don't have to worry about the
linear range. As for vibration measurments, you will have to make sure that
you stay in the linear range of the probe.

I want to make sure I understand what you meant by having a filter at the
resonance points.
Are you only going to measure vibration at resonance (i.e. bandpass)?
Or, are you NOT going to measure at resonance (i.e. notch filter)?
Keep in mind other events may cause vibration, such as impulse, rub, etc,
which will likely occur synchronous to the shaft, and have nothing to do
with resonance.
This is where a phase reference may be handy because you could determine if
it is happening 1X/rev, 2X/rev, etc.
OR, are you assuming that an impulse/rub event will excite the case at the
resonance frequency?

At any rate, what you intend on doing is definitely do-able.
I recommend playing with probes a bit to see what you get.
Sounds like a fun project.
Let me know if there's anything I can offer...

Adam


"RST Engineering" wrote in message
...
Proximity probes? Or accelerometers?

I understand about the analog circuitry and actually plan on making a five
or six channel filter at each of the possible resonance points relative to
the fundamental ... and then strobing the filters to light a "normal",
"low", "high" lamp for each channel.

Jim




As is tradition, we tend to get off topic ;-)
I think you can accomplish this using the methods discussed.
Mount 2 proximity probes 90 degrees apart.
Calibrate the readings for normal low vibrations (be sure to account for
any nonlinearities in the probe).
Design the circuit to trip the buzzer/lamp when the vibration exceeds the
normal level.
You may need some analog circuitry to help (gain, etc).
But you don't need to get much fancier than that.

Adam

Well, a Spectral Dynamics SD2001 FFT would be well received if you have one
laying around unused {;-)


Jim



"mindenpilot" wrote in message
...
At any rate, what you intend on doing is definitely do-able.
I recommend playing with probes a bit to see what you get.
Sounds like a fun project.
Let me know if there's anything I can offer...

Adam

In article ,
RST Engineering wrote:
Proximity probes? Or accelerometers?

The proverbial "it depends". _first_ you have do decide what your
'frame of reference' for vibration is. If you're looking for
excursions in the drive shaft, relative to the engine block, then
a pair of proximity sensors in quadrature to measure excursions from
the shaft axis, plus a strain gauge at a fore-to-aft thrust bearing
gives you complete data. Convert from XYZ to polar co-ordinates,
Fourier transform on the magnitude component, check each passband
against loading-corrected reference values, and illuminate corresponding
indicators.

If you're looking for things that might affect all parts of the engine
equally, then, can you use the airframe for reference, or not? If "yes",
then the same approach works, just on a different scale. If, "no", then
you're pretty much stuck with three _inertial_ accelerometers, mounted at
mutual right angles.

I understand about the analog circuitry and actually plan on making a five
or six channel filter at each of the possible resonance points relative to
the fundamental ... and then strobing the filters to light a "normal",
"low", "high" lamp for each channel.


Sounds like you're talking about using a group of narrow bandpass filters
and sampling the short-term average signal level out of each filter,
"Looking for" a marked increase vs a base-line reference (at that frequency),
as an indicator of problems.


I see a couple of difficulties -- not necessarily insurmountable, but
there, nonetheless. (1) Most, if not all, the 'frequencies of interest'
are dependent on engine speed. thus the filter 'center frequencies'
will have to track engine RPM. (2) "Normal" vibration _magnitude_ will
vary with the load on the engine. The trigger threshold would seemingly
have to adjust to compensate. 3,000 RPM in a 2,000 FPM climb is a
different engine environment than 3,000 RPM in level cruise. I don't
know enough engine mechanics to guess whether just the throttle setting
is going to be sufficient to determine the required adjustments. At
a guess, torque relative to the airframe would be a better indicator.

Lastly, I'd suggest one channel that is comparatively broadband. specifically
to catch unanticipated "out of band" goings-on.

Jim




As is tradition, we tend to get off topic ;-)
I think you can accomplish this using the methods discussed.
Mount 2 proximity probes 90 degrees apart.
Calibrate the readings for normal low vibrations (be sure to account for
any nonlinearities in the probe).
Design the circuit to trip the buzzer/lamp when the vibration exceeds the
normal level.
You may need some analog circuitry to help (gain, etc).
But you don't need to get much fancier than that.

Adam

"RST Engineering" wrote in message
...
Understood. What I started out to do (and still plan on doing) is to have
a device that will stay permanently mounted to the engine that can be
calibrated (adjusted, signed, pick a verb) when the engine is known to be
good and light a "your engine is about to come apart" lamp at the
appropriate time.


Excuse my ignorance, but couldn't you just feel the vibrations?

If you wait that long, you're probably more concerned if the chain that's
holding the motor to the firewall is going to break after the motor cuts
loose from the mounts. All too often, the vibrations start to pick up
seconds or miliseconds before a catastrophic failure.

To do such a health-monitoring function properly, you really want some
seeded fault data to characterize what a "bad" engine spectrum looks like.
How many engines do you want to sacrifice to get the data? You can approach
it from the "anything different from a healthy engine signature" standpoint,
but that will likely result in a ton of false positive fault indications.

"LCT Paintball" wrote in message
news:_Lq0e.14520$fn3.9681@attbi_s01...
"RST Engineering" wrote in message
...
Understood. What I started out to do (and still plan on doing) is to
have
a device that will stay permanently mounted to the engine that can be
calibrated (adjusted, signed, pick a verb) when the engine is known to
be
good and light a "your engine is about to come apart" lamp at the
appropriate time.


Excuse my ignorance, but couldn't you just feel the vibrations?