Distance Measurement

I would suggest a LVDT probe.

As its moving at speed a high frequency version should be used say 10 kHz.

1 micron resolution is no problem 2 micron accuracy might be depending on temperature changes in the fixture etc...

I designed the range of Solex gauging instruments in the early 80s and with the correct design of fixture an accuracy of 2 microns is quite feasible.

John.

it looks like you want a displacement transducer... ya.. u can go for LVDT which can measure high frequency displacements n give good accuracies.. there are other types of displacement transducers like eddy current, capcitance and laser all non contact type n (ofcourse expensive) giving you the output in analog or digital and the required accuracy in micron..

'200 times per se' - I take it '200 mm per sec'

I am afraid at this speed there will be some rebounding action at LVDT. Still thru proper programming of whatever software u are using for cpaturing measurement you can use it.

Otherwise Smart Sensor (Laser sensor) is the best potion.

thanks, where can i find laser sensor details ,will it satisfy my speed requirement and accuracy.

Omron, Keyence, Banner are the best in the field, as per my knowledge.

Visit their web site to download brochures.

I have following doubts.

1.for what extend LVDT can be used, or how many strokes that can be applied to LVDT

per sec.

2.Another thing is,the metal rod always in oily surface ,so laser will sense the metal or sensing distance affect due to oil surface.

1.for what extend LVDT can be used, or how many strokes that can be applied to LVDT per sec.

I can't really say to how many strokes per minute LVDT is o.k. But we are having a setup where LVDT is used for a stroke of 10mm per sec. It is working fine.

2.Another thing is,the metal rod always in oily surface ,so laser will sense the metal or sensing distance affect due to oil surface.

That's a good point. Laser may creat problem for oily surface. But, if you can assure that the suraface is wiped properly so that the layer is really very thin, it will give consistent results. Don't use it on surfaces smeared with oil.

Dear Electroman,

May be you are right, provided the LVDT is attached with the object. But, I don't think it's practical to attach the LVDT to the object every time in normal production or testing. If Mr. Moorthy is comfortable with it, no issue.

We used LVDT for testing the overtravel of Contactor & faced a lot of problems due to rebounding. We used spring to reduce rebounding. But, when the spring force is less rebounding was more & when it is more the force on the object is more giving wrong readings. But, somehow by using LABVIEW we captured the contacts & made a program to pick the correct one.

As far as the accuracy is concerned there are sensors with 1 micron accuracy, I have used one myself. Pls refer mnufacturers I mentioned earlier.

moorthi, forget lasers they will not be accurate enough, at best you may get an accuracy of 20 microns...

the only solution is using a LVDT probe as I said in post #1 they are designed for extreme longevity with moving targets...

I think someone said they will rebound or something - that is rubbish! they can be attached to the target so that the moving ferrite slug is not touching any thing giving it a lifetime of use even at these frequencies.

John.

thanks,

LVDT and LVDT probe are different?

The basic LVDT probe (Linear Variable Differential Transformer) consists of a coil with balanced sides excited by a sine wave signal, inside the coil is the armature which can be sring loaded, in a bearing or completely non contacting with the coil...

This armature is basically a ferrite core that moves inside the coil to change the signal induced in the output coil, the phase and the magnitude gives the direction and displacement of the core very accurately.

There are two basic types of LVDT full bridge or half bridge, the half bridge shouldn't really be called a transformer, but it saves time!

Because the coil can be excited by a high frequency they can be used for accurate measurements on moving targets, such as you have.

They can be purchased to cover measuring distances of less than 1 mm to over 1500 mm together with the drive and conditioning electronics necessary.

John.

Very thanks electroman for yor ideas about LVDT .

if i have any more doubts , i contact you. can you give me your personal

E-Mail Id ?.

moorthi.

No problem! you could just use the CR4 email system or if you want to use:

john AT marchdesigns.com