Slow Roll from 3300 sereis non contacting probe

[Eager to Know]

Slow roll recorded by the probe is combined effect of mechanical and electrical run out. If the mechanical run out is zero, then any reading value is due to the electrical run out. Electrical run out is based on magnetism of the material.
Question is what types of material properties such as molecule structures, shape, size, or number affects the magnetism of the material and how to reduce it. Also what is the relationship of magnetism value with the out put from the probe?
Thank you,

[mattkoly]

I've recently had an issue with chrome coatings on the shaft of our BFP where the shaft was not burnished. We found that thickness of the coating determines how much it affects the "magnetism". Bently suggested calibrated proximetors but the coating has to be thicker then 20 mils for it to be most affective we are only at 7-10 mils.

That said I'm pretty sure that if you have an uncoated shaft of any metalic material you can have the prox calibrated to work properly otherwise the bently proxes come calibrated for the 4140 Steel

[Steve Sabin]

You will find this ORBIT article on runout to be helpful.

It deals with some of the questions you have regarding what causes runout and how to mitigate it. It also talks briefly about shaft coatings and their impact on proximity probe readings.

For additional information on this topic, you may wish to contact our technical support team at bntechsupport@ge.com or your local salesperson. All of our customers are entitled to free phone and e-mail technical support, as detailed in this recent ORBIT article on Technical Support options/coverage.

If you do not know who your local salesperson is, contact us via the tech support e-mail address above and we will put you in touch with the correct individual(s) within 2 business days.


Regards,

Steve Sabin
Editor, ORBIT magazine
GE Energy

[Steve Schultheis]

My experience has been that precipitation hardened steels have weird magnetic properties that can increase electrical runout. 17-4-PH is a good example of a material that you probably want custom calibrated probes for.

Standard degaussing techniques ususally work well for 4140 steel.

[constovich]

Material science is way beyond my understanding (electrical engineering), but we performed a study on our SG Feedwater Pumps (similar to BFPs) for electrical runout concerns relating to valladium pockets in our 4140 shafts. There wasn't much of an issue though as they found these pockets only contributed about 1 mil to the runout.