Looking for several basic questions

I use a datapac 1500 and odyssey 2.3. Do I have to buy the amp probe from (the expensive) Ird people? Can I buy any amp probe with some sort of ac voltage output and plug it into the data collector? What kinds of costs do you think i will see?

Will the normal Entek software work? Program points, collect the data, analyze the data?

Is the analysis like analyzing vibration (obviously meaning to somewhat of a degree)?

The customer is requesting this. How many people feel this is a valid science? Is it a significant stand alone tool or is it just another tool in our reliability box to be used in conjunction with others?

I will research this on the internet but am always interest in hearing direct responses.

Thanks, Joe

There are a variety of probes required, you don't have to use one from Entek.

We collect current data with our Datapac and E-monitor software. We look for pole-pass sidebands around 60hz as possible indication of rotor bar problems or dynamic eccentricity. Level of concern is somewhere in the neighborhood of 1% of the main 60hz peak... although lots of numbers are out there... some a complex formula depending on speed, horsepower and number of rotor bars.

There are other more exotic features available from folks like pdma including looking for 1*LF, 3*LF etc sidebands around RBPF in current as indication of eccentricity. I understand there is some special filtering or demodulation required to do this due to dynamic range limitations (these components are orders of magnitude below the 60hz component). I haven't tried to do this with our setup.

I use a standard Fluke clamp-on current transformer (about $100.00) and made a resistor box to convert current to voltage. It cost less than $20.00 plus my time to make it. It works fine with CSI 2120 analyzer (and 2110 previously). I have not only found motor faults, but also gearbox, vee belt, and hydro turbine faults. It is a great addition/supplement to vibration monitoring and analysis.

Clamp probes have various frequency responses, some responding to little above 60 Hz, others being broadband. Check the spec sheet to be sure the amp clamp can handle the frequency range required.

The resistor Walt mentioned is extremely important. Without a load, some current transformers will develope several hundred volts - certainly enough you won't soon forget it if you get your hands across the contacts. Your instrument may not be too forgiving with such a large input either!

One technique in the old days used a loop of wire to pick up the magnetic field from the motor. The more turns of wire, the greater the signal. An easy way to test this idea out would be with a piece of ribbon cable and a pair of IDC (crimp on) connectors. Install one of the connectors 1 pin off, so that when you plug them togeter, you actually end up a single conductor wrapped around the motor with many turns. I know you will get a signal this way....but other distractions got in the way of doing anything with the data.

Jon
Spintelligent Labs

Vendor,

John, we have a gadget, a flux probe:
http://www.vtab.se/index.php?page=71&lang=en
that is in a way what you describe but in a more handy package. It works and give data that looks like what you get from the clamp, and more, if you place it consistently it can be trended. Popular in Australia, no battery, just hook up to something that have good sensitivity like 1mV/g or 10mV/g compared to a normal accel input. Otherwise I use LEM Heme clamps that use Hall element sensors for good frequency response. Olov

Joe:

One of the reasons for the high cost of Amp probes for Current Signature and Electrical Signature Analysis has to do with the accuracy of the data to be collected. For instance, in the ESA devices that I used to be responsible for (ALL-TEST Pro), we required a 0.5% accuracy across a 20kHz frequency range with a 0.5 to 1.5 degree phase shift. The average cost of these probes was ~$450 USD each. On occassion, when I needed to provide up to 3,000 Amps, we would use a probe with a lower resolution (accurate to about 3,000 Hz). There was a noticeable difference in accuracy of analysis.

So far as the analysis goes: Yes, it is a lot like vibration analysis. The demodulated spectrum is primarily used below 300 Hz for the detection of problems such as vibration, belt problems, bent shafts, etc. (the low running speed harmonic stuff seen in vibration). The primary difference, when looking to the current spectrum, primarily in the higher frequencies, is that you will normally see sidebands of the frequencies you would calculate in vibration (line frequency and running speed, depending on the type of fault) but not the actual frequency.

I am providing a copy of the AC portion of a data interpretation manual that I put together while with ALL-TEST Pro (I am now working for a Military/Industrial maintenance and reliability consulting firm). The work that I completed on DC analysis (evaluating DC motors, drives and driven equipment using electrical signature analysis), generators, machine tools, synchronous machines, etc. will be in print within the next few weeks.

If you have any questions related to MCSA or ESA, please feel free to respond to this, or email me: howard@motordiagnostics.com. I am not an instrument vendor (anymore).

Sincerely,
Howard

ATPOL_Desk_Guide_and_Pattern_Recognition_Manual_AC_only.pdf (652 Kb, 85 downloads) ATPOL ESA Desk Guide, Induction Motor Portion Only

Will a standard fluke probe with a 1mv/amp or 10 mv/amp output work well?

What is the difference between measuring amps or voltage? Do you need or want to analyze the voltage?

If the meter had the mv output and a bnc connector, can I just plug this straight into my data collector?

Joe:

Not sure, it has been a long time since I used a 1500. It will depend on if Entek is using any type of conditioning hardware in their probe. I will have to see if I can find out.

As far as the other question:

Current provides an analysis of the downstream points from where you are testing (ie: motor, connections, driven equipment).

Voltage provides an analysis of the upstream points from where you are testing (ie: generator, DC drive, VFD, power quality issues, etc.)

The problem, when testing just one or the other, is that you have to determine which are signals that indicate a downstream problem and which are upstream.

Consider this: In the case of ESA or MCSA, the electric motor is the transducer (actually, the airgap between the stator and rotor is the transducer). If you input a perfect sinusoidal voltage into the motor, you should receive a perfect sinusoidal current back, in a perfect circuit (which is highly improbable, in real life). If you have imperfections in the voltage signal, those will be reflected back along with the imperfections in the current signal due to defects. This is because small imperfections will occur in the airgap (magnetic fields) due to the voltage plus due to rotor movement within the airgap.

In either case, it is seen as the rotor moving within the field. By following the inverse square law (intensity varies by the square of the distance), the small changes in distance within the airgap (either due to variations in the field, or rotor movement) translate directly to imperfections in current.

By viewing both, you can determine if a problem is due to incoming signals (voltage) and outcoming signals (current) by looking at the magnitude of the peaks in dB. Also, you can identify potential problems by actually knowing what the potential signals are, for a given fault.

To further explain, please see the note slides of the presentation on ESA that I performed for the 2005 Michigan Vibration Institute general meeting (attached). Unfortunately, animation does not translate to Acrobat.

Sincerely,
Howard

ESA_Evaluation_Michigan_Vibe_Inst_2005.pdf (277 Kb, 54 downloads) ESA Presentation 2005 Vibe Inst Michigan

Joe,

Most of the "standard" Fluke clamp-on current meters (and similar brands) that have a voltage output are not suitable, because the output is DC and not an AC voltage signal. You need an AC voltage signal proportional to current that has a suitable bandwith (see Howard's comments). I have been using a Fluke 80I-600 with home-made resistor box. You could spend about $125.00 for this setup or $450.00 or more one that is ready to go; and possibly more accurate.
If you are handy with a solder iron and able to study from Internet information, then you can potentially save some money (may have limited measurement capabilities). If you are using company $$ and want to get going quickly and properly, then purchase a quality system with detailed user manual and get some onsite training. Either way, you will find motor current analysis to be a very powerful monitoring and diagnostic tool.