Is this with a Bently Nevada system, in which case it is abnormal? The obvious question next, if you are using a voltmeter are you observing proper polarity conventions at the voltmeter? Give specifics of device that is providing this positive bias and how you are attaching to the measurment point.

Dear Mr. John, I have a question about the DC GAP positive, in one Steam Turbine I found the MMS 3119 Dual Channel Shaft Vibration Transmitter (that works with DC GAP positive) I used the portable DAIU 208 to collect the data, but the Shaft Center Line plots were completely wrong. I will appreciate your advice in order to collect the data in the proper way.

RamonG posted:

Dear Mr. John, I have a question about the DC GAP positive, in one Steam Turbine I found the MMS 3119 Dual Channel Shaft Vibration Transmitter (that works with DC GAP positive) I used the portable DAIU 208 to collect the data, but the Shaft Center Line plots were completely wrong. I will appreciate your advice in order to collect the data in the proper way.

I am not familiar with the MMS 3119 Transmitter so you should perhaps be dealing with the people that make that transmitter to see what you can do with ADRE.  A quick look at the online spec sheet makes me think you can do very little with respect to diagnostics.  In particular there is a description of the "Outputs" that reads "Two test outputs, one for each channel, proportional to the dynamic input signal; also to be used for analysis and diagnosis purposes; cable connection via cage clamp terminals."  Use of the word proportional makes me think that you don't really have the dynamic signal needed for example for a spectrum.  Since the manufacturer is German, it could be a poor choice of words used for the translation.

I can tell you that the Bently Nevada 990 Transmitter also supplied a positive DC output and would do as you describe.  But there was also an accessory that would correct the polarity of the DC gap information and provide isolation.  These were to be used with the Adre 208P.  The use of the adapter is well discussed in this forum earlier.  Go tp the thread at https://www.maintenance.org/to...8#399590942964580878 and review my content (two separate entries) about the 990 Test Adapter near the bottom.

There is also related content, including the 990 Test Adapter User Guide as an attachment to one of my responses at https://www.maintenance.org/to...3#399590942963410793.

 

 

 

 

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