I just wanted to get some practical recommendations from you guys taking vibration readings in high temperature applications, such as heated rolls, where bearing surface temperatures may reach 300F +.

Are you using special accelerometers? (General usage accelerometers are limited to 250F.) High temp accelerometer with a charge amplifier is in $1500 range.

Is magnet's pull affected by high temperature?

Do you think that inserting a plastic thermoinsulating washer between a regular accelerometer and magnet will help?

Thanks

This message has been edited. Last edited by: David_G,

In the past I have used a large magnet, and since th transducer is standing off about an inch it is not seeing 300 F. Unfortunately the old Bently rail magnets used a potting material to hold the rails, and on the hot end of a Frame 3 I found the accel had dropped to the floor because the mag base melted, leaving the rails on the machine.

David,

My understanding is that rare earth magnets loose their strength above 300-F. You should verify this if planning on using a magnet. Also beware of cable insulation temperature rating. A few companies sell ICP-type accelerometers rated to about 350-F. Higher temperatures usually require a charge-type accelerometer with high temperature cable and an ICP-charge converter. Check with CTC, PCB/IMI, Wilcoxon, B&K, and Endevco.

Insulating washers, metal stand-off mounting, air and water cooling can be considered. Beware of changing frequency response and be prepared to have backup accelerometers if you "cook" one or more while experimenting.

Walt

The CTC guy showed me a high temp accel like walt describes last week.

It has a charge mode accel mounted by a steel tube to a charge converter.

Those old IRD mags were even larger as I remember. PCB makes a good hi-temp model. Paper machines won't take the run-of-the-mill transducer or a lot of hot stuff. You may also want to look at Kistler and all for that matter.

I have some permanent mount Wilcoxon 376E's with charge amps on some 450 F stuff here. Seems to be holding up good, knock on wood. I don't care for the little bitty micro dot cables though.
I also have a ceramic mounting pad I haven't tried out yet. This mounts between the accel and mounting surface. It's 5/8" thick x 1 1/4" OD. It has 1/4" 28 metal inserts to screw into on both sides. It's an IMI 080M274. Might be what your are looking for.

Thanks for all good responses.

This is an one time job, so unfortunately no ceramic pads or charge amplifires... and therefore at this time I'm trying the "band-aid" approach. I hope that inserting a nonconducting washer between the accelerometer and the magnet may reduce heat transfer. Still have concerns about magnet pull though.

I wonder as to what the paper plants guys are doing in this regard?

David

David,

Here is an idea if you are trying to cope with a 250-F accelerometer on a hot surface: mark the accelerometer case with a temperature crayon or stick-on marker. If it melts or changes color, then accelerometer case is too hot.

Walt

that's good Walt! Only monitoring a few points? Use a cool heat sink like a bucket of ice, 5 magnets and switch every 5 points --- hey, you never know. So it take an extra hour to do the job but saves $500 in expense! A one-time job with a created situation that allows you to use the transducers you have providing the resolution is good enough. I've used PCB's good to 0.05 Hz @1 V/g on some hot stuff. Will your situation allow a 10 mV/g?

David,

I have done calendar rolls that were steam heated to 350. I used IRD's big 65# pull rail magnet, and a bucket of water. I kept one magnet in the water, and switched out when the one I was using got to hot to hold.

I couldn't see any difference in the spectra from a cold one to hot.

Dave

CTC has 1/4 turn
Quick Connect Fittings You could drill and tap the 'stud' (threaded) and attach it to the magnet, and the 'receptacle' screws into your accel (studs are $9 ea. and the receptacle is $30). Mount your magnet to the machine, 'quick attach' your accel to the magnet, take your reading, and then dismount the accel. This will also minimize the change in readings as the accel heats up, as it would never get that hot. You could set up 2 magnets this way and switch them out when one gets too hot. You might could place your insulating washer between the magnet and the stud also.

This message has been edited. Last edited by: rustythevibeguy,