Dear All,

I am currently using DI 440 FFT analyser. i need to carry out a 2-plane balancing on a compressor assembly bundles with a coupling each between gearbox and stage-3 compressor and another between stage-2 and stage-4 compressor. i can go for mass addition. the speed is 9000 rpm. the concern is not balancing. my client is not allowing me to put a reflective sticker (to measure RPM and phase) on any one of the coupling due to safety reasons and oil splashing. he says its impossible....!!! can i do the balancing by using bently vibration panel by taking displacement readings from 2 planes (2nd and 3rd stage comp bearing). if yes then what are the settings i need to make in my analyser (it has a 2-plane balancing mode) to get the input from the key phasor provided on the panel for my RPM and phase. do someone anytime carried out this kind of exercise...???

matter urgent. i only have 2 days to go. i need to send a reply for my client. please help.

if required i can send the settings available in my DI 440 vib kit. it has 2 inputs for tach signals (analog and ext TTL).

Warm Regards and Happy New Year. hope i will get a reply from someone.

Madhusudan

Key phasor should be +/- 5V TTL I think - just input to the jack on your analyzer; may be on the back panel. Sens should be 0.1 V but you are only needing relative so that should be close enough. Normally I ground first and insert the bannana jack I've never had a shut-down this way.

You aren't offering the best information about the BN monitor so let me give you some general information.

I'm assuming that the BN monitor is connected to BN proximity probes in which case your analyzer should be set up for a scale factor of 200 mv/mil or 7.87 mV/mm.

Assuming the system has a Keyphasor routed to the BN monitor then you should be able to connect to the front panel BNC connector labeled as the Keyphasor. I'm not familiar with your analyzer but I would try running the signal into the analog input. It is possible that both will work.

In your next post be more specific as to the type of BN monitor (5000, 7200, 3300, 3500) and we can be more specific in helping you.

John from PA

Hi John and Sam,

Thanks...!!!

the panel is Bently BN 3500. here are the settings available in my DI 440 FFT analyser under 2-plane balancing.

Advanced Set up:

FILTER: 2 HZ
DETECTION: RMS/PK/PK-PK
NO OF AVERAGES: 3
SOLUTION: INFLUENCE/COEFFQUASI STATIC
<PLANE>: ALL/1/2
INPUT CHANNEL: CH1/CH2
COUPLING: AC/ICCEL
SENSITIVITY: ANY VALUE I CAN INPUT
TYPE: CONTINUOS/FIXED
NO OF POSITIONS:
POSITION 1 OFF SET:

BALANCE SET UP:

NO. OF PLANES: 1/2
VIB MEASUREMENT TYPE: ACCEL/VEL/DISP ETC
WEIGHT UNITS: g
LENGTH UNITS: mm
MOVEMENT: WITH ROTATION/AGAINST ROTATION
TRIGGER TYPE: EXT ANALOG/EXT TTL
EXT TRIGGER SLOPE: +VE/-VE
TRIGGER LEVEL: ANY NO. I CAN INPUT

Hope i had given all the settings available in my FFT. expecting an early response.

arm Regards,

Madhusudan

Not sure what type of compressor you are trying to balance. Some do not have a speed input to the BN panel. In most cases these are very high speed machines and I am not sure I would recommend field balancing the rotors.

Can you examine the machine train or do you know where the keyphasor is located? I noticed that you said there is a gearbox involved. If the keyphasor is mounted relative to the low speed side of the machine train then it won't do you any good in balancing the 2-3 stage compressor. You will have to get some type of phase reference related to the 2-3 stage rotor.

Have you done balancing before? This is a relatively simple exercise for someone with experience but if you have never done this I would suggest you get someone with experience the first time and observe and work with the person so you can learn.

John from PA

Madhu,

The Key Phasor output is not TTL signal. It is a dynamic signal that depends on the target type Hole/slot or key and the prox probe gap setting. The best bet is to look at the waveform with the analyzer data channel (scale as voltage sensitivity = 1.0) so you can see whether signal is positive or negative and to pick a good trigger level.

I suggest you do a coastdown or slow runup so you can understand the rotor dynamics and find the heavy spot so that you can put a trial weight in a good place.

Walt

Hi,

I had done several on-site balancing assignments till date. yes the key phasor is available for compressor shaft which rus at 9000 rpm and as told earlier its a BN 3500 make. let me know what are the settings i need to make to tap the RPM and phase in my FFT.

Warm Regards,

Madhu

Why not try the 4 run method, which is without phase? When we had a factory rep from Cooper on sight, that is what he did.

First, I would check out the trigger signal with an oscilloscope. Your DI may serve this purpose. Make sure the signal is there, and then determine your settings.

Mick what is this 4 run method without phase, i had heard of 120 deg method but never heard of this earlier. can you send me the procedure please. my mail ID
n.madhusudan@diagnosticengineers.com

William i do not have an oscilloscope. yes the key phasor is active at site. its confirmed by my client. i had mentioned the setting options available in my previous reply. please note i will get only one start and stop a day and its a 2-plane balancing procedure i need to adopt and its a 5 days shut down so that means
initial run: day-1
trail 1 in plane-1: day-2
trail 2 in plane-2: day-3
correction mass: day-4
trim balancing: day-5

that's it. i will not get a 2nd chance.

Warm Regards,

Madhusudan

Madhu,

You don't need an oscilloscope! You have one, if you use your analyzer in waveform display as I suggested. I can't say specifically how to set your analyzer, since I have a CSI 2120. It should be very easy to look at the Key Phasor waveform and then make your analyzer tachometer settings.

Walt

It's not clear what your machinery is, but I would be tempted to run a consultant out of the facility if he/she wanted to use the 4-run method (without an indication of phase) on a high speed compressor.

Don't assume that the signal from the trigger is good; look at the signal.

2 plane balancing without phase is a 7-run method.

madhu,
To tap the keyphasor signal from the BN panel, you need to set your analyzer to pick up the trigger voltage of the keyphasor. You can do this by setting your analyzer to show the keyphasor waveform and your analyzer input to voltage... hope this helps...

Cheers,

I thank one and all for giving me all the suggestions. Yes finally i got the settings made in my anlyser and now my DI 440 is showing RPM and phase through key phasor and magnitude from the disp probe under balancing mode.

Madhu