Transducer sensitivity = 200 mV/mil for eddy current probe:

I'm using a CSI 2120 and it set the sens to 0.20 V which would be 1 mil 0-P??????

On RTA's I use 100 mV so the reading will be P-P.

Is there something funny or different about the 2120??? I'm not being funny! BTW!

Thanks in advance.

Sam,

The sensitivity should be set to 0.2 V/mil as you did. There is seperate setting for RMS, Peak or P-P. Go to: Utility -> (3) Change Setup -> (4) Data Units [select Displacement PK-PK]

Make sure your measurement point is set for displacement sensor: Utility -> (3) Change Setup -> (3)Sensor Type DISPLC and Convert To DISPLC and make sure SENSR PWR is OFF {no ICP}

The BMW of the vibration analyzers takes some getting used to!

Worse than that - the jags went by blowing the doors off!
I have found that the analog setting processes acceleration by integrating to velocity and then processed to TWF and back to acel which has ~10 higher amplitudes in the spectra than the initial acceleration spectra under analog? WOW! But it still looks like velocity in shape and pattern rather than acceleration???????? Anybody?????????????????????

Sam,
I am not sure what you are talking about. Your initial question was about proximity probe. That signal is not integrated by analyzer. A 0-P or P-P value is calculated from RMS value as many analyzers do. If you want true peak or true P-P, then pick values from waveform or set these as measured parameters with MasterTrend or RBMware.

Now if you are using an accelerometer, then integrate to get velocity. Either analog or digital integration can be set. Analog integration gives a velocity waveform and spectrum. Digital integration gives an acceleration waveform and velocity spectrum. The quality of the analog integration depends on the "Pole" setting. A spectrum display in MasterTrend/RBMware can be forced to accel, vel, or disp rather than the acquired units. The quality of the overall level from the spectrum is based on the RMS value and is affected by F-min and F-max and dynamic range issues. As far as your ???? goes, just be sure your settings (input adapter, sensor type, sensor power, units, and integration type) are consistent. Hope this puts the Jags in their place.

I was looking at a displacement probe with a sens of 200 mV/mil which is 0.2 V mil 0-P. The CSI uses 0.2 as the sensitivity which is mils 0-P unless they are doing something inside. That was the original question.

But as far as cars go: after having BMW's and Jag's - no comparsion - I'll take the jag any day. Which is not to say the BMW is bad - just not my cup of tea. But the 160 mph days on the highway are over.

then to the signal processing: using an accelerometer, the 2120 integrates to velocity and then processes a TWF and then calculates the spectrum and differentiates it back to accel. I have found if you use digital processing and digital pk you will get values ~10x higher than processing in analog???... Don't know why?

I've never seen that using RTA's (HP, Ono Sokki, Nicolett, etc... or with others); just found it puzzling - no explaination!

Sam,
If you use analog integration the waveform will be integrated to velocity then there is no integration when generating a velocity spectrum, my personal choice to help keep down the integration ski slope. Then you will have a velocity waveform stored unless I take a special time waveform in acceleration (which I do). The special TWF has it's own settings for f-max and points stored. If the special TWF has a lot higher f-max you could possibly have a lot higher waveform amplitude. If you don't store a special TWF, you get what you get, it doesn't integrate the waveform then differentiate it back to acceleration.

Sensor sensitivity doesn’t have a 0-P or PP with it. Sensitivity is V/unit (or similar mA/(m/s), mV/mil, pC/g, etc).

Particularly, in the old days, when instruments had limited display scaling options one would include a correction factor. To get pseudo 0P from a 100 m V/g accelerometer, one might have to use a calibration factor of 0.070711 V/g. PP would be 0.03535, etc.

[QUOTE]Originally posted by Sam Pickens:
I was looking at a displacement probe with a sens of 200 mV/mil which is 0.2 V mil 0-P.QUOTE]

I don't have a CSI box, but the scale factor on a general proximity probe is 200 mV/mil. There is no 0-pk or pk-pk implied. Whether you collect/view the amplitude in 0-pk or pk-pk is independent of the transducer scale factor.

As Bill correctly points out: we used to input 0.0707 on a 100 mV transducer (acel for example) to get a 0-P reading else 100 mV sens gives RMS. But also we input 100 mV on a 200 mV/mil (EU) eddy current probe to get P-P else 200 mV sens gives 0-P reading.

The old SD 240 & 345 & 375 used this but Ono Sokki allowed input of the trans sens for a 0-P - before PC's or pre '83 and pre-blk/bx.

quote:

As Bill correctly points out: we used to input 0.0707 on a 100 mV transducer (acel for example) to get a 0-P reading else 100 mV sens gives RMS. But also we input 100 mV on a 200 mV/mil (EU) eddy current probe to get P-P else 200 mV sens gives 0-P reading.

The old SD 240 & 345 & 375 used this but Ono Sokki allowed input of the trans sens for a 0-P - before PC's or pre '83 and pre-blk/bx.

I think the key words here are "used to".

I used to use an HP RTA and a tape recorder back in the 80s and when we got the CSI 2100 meter and a DOS version of Mastertrend, all those adjustments for the transducers and Db settings for the sound from the tape recorder were not used anymore. Trying to use setups and "tricks" from older (if that is the correct word to use) analyzers is not going to work on these modern day high tech analyzers and expect to receive the same amplitudes, etc. from them through a 2120.

But on the other hand, the tape player could be fed through the 2100 and actual data store as if using a normal transducer, but adjusting the sensitivity was a chore. Was not worth the trouble.

quote:

But as far as cars go: after having BMW's and Jag's - no comparsion - I'll take the jag any day. Which is not to say the BMW is bad - just not my cup of tea.

Is this saying a 2120 is a BMW?

By The Way: Is "0.0707" the correct number used for going from RMS to Peak? Seems like it is 0.707, I may be wrong though.

0.070711 was the correct calibration factor to get psuedo peak when using a 0.1 V/unit transducer.

Modern instrumentation allows one to input the sensitivity and not have to play with correction factors to get the display correct.

quote:

0.070711 was the correct calibration factor to get psuedo peak when using a 0.1 V/unit transducer.

Thanks, Bill.

What is "psuedo"?

Yeah; 0.707 is the rms value of 1. So if you look at a volt, the sinusodial wave's peak is 1 and you multiply 0.707 to get the rms - since 0.1 is 1/10 then 0.0707 is correct for 100 mV.

I was not talking about analyzers but sensitivity. The analyzer shouldn't matter. Eddy current probe of sens: 200 mV/mil. Now with that known (it's the transducer, not the analyzer) the 200 mV movement from 10V?? or is one mil 0-P as I understand. So, if you want a displayed reading of P-P you would set the sens to 0.1 --- that was my question. Now I will admit that I may have muddied the water (not sure). But was asking for a clear understanding of that aspect only. Has it been answered? Does the 2120 take into account that if you check displacement it automatically knows and corrects????? It was clear to me and I was asking - sorry for the confusion.

0p, pp, and rms are measurements. Sensitivity is something else. Most analyzers today should handle the measurement in the way you desire given a sensitivity or calibration constant for the input.

You have a (in this case) voltage coming off the transducer. For a 200 mV/mil transducer, a 0.200V change in the voltage is a change of 1 mil. Look for the change over a period of time (I don’t know if there is an agreed upon standard for how long or number of rotations, etc. over which to measure.) to get 0p or pp. 0p for a proximity probe is a little more tricky since you have to get rid of the DC to get a 0 reference point; after all this is a relative measurement transducer, and position relates to the DC content of the signal. Similar for an rms measurement, but you don’t look at the maximum change over a period of time.

Any change of 0.2 V represents a measurment change of 1 mil over the linear range for the transducer/instrument systems. This calibration is the slope of volts/mil (or other units for different transducers) from a series of measurements, i.e. the callibration curve. Actually, one is better served by doing a statistical fit for this curve than just taking a couple of points to do a calibration.

With an absolute (Is anything really absolute?) type transducer or one that doesn't measure down to dc or have a dc bias, the voltage can be measured (always relative to something, like ground potential) to give the g level or what ever. If the measurement were to be g's the measurement would really (most likely) not include the dc acceleration of gravity, because most accelerometers used for vibration don't measure this. Then there is the whole frequency response stuff related to the measurement. Too much on a simple subject that I may just have complicated.

This message has been edited. Last edited by: William_C._Foiles,