Need advice on the purchase and use of LVDT instruments

I started this thread as a clean slate for discussing LVDT purchase options and the techniques for using them. This acts as a clean followup to my previous thread, "Considering precision TIR and OD/ID inspection equipment purchase", where we ended up discussing anything but how to choose or effectively operate an LVDT linear gauge. On this thread, please refrain from discussing matters of equipment and how tight tolerances are going to be achieved on my machine. I am only concerned with metrology and gaining an actual answer to the questions addressed in the OP of the aforementioned thread. I don't want to move forward with any purchase until I have gained enough insight on the subject to make an informed decision.

Brands and type: Looking back at the OP of that thread, I describe the things I want to measure and why they are important. I want to move from the why to the how I am to conduct these measurements. So, with brands such as Mahr, Etalon, TESA and Diatest as well as the many models offered by each, how might I choose which is most suitable for me? Are there any advantages with certain brands? I don't need a long stroke plunger setup; I only need what is necessary for TIR inspection and OD/ID comparison.

Required equipment: I'm having trouble finding information on what equipment is actually needed to use an LVDT and get a reading. I am particularly at odds with the terms, "gauge amplifier" and "indicator" for electronic gauging. From what I figure, one describes the instrument, or "box", to which the LVDT is plugged in that translates the electronic signals into a displacement measurement, while the other is supposedly a separate item that conducts the "amplification". This is the main page I am consulting for equipment with which to read the Mahr 1318's output.

For the "compact amplifier", "column amplifier" and "measurement interface", these seem to mainly differ in input capacities, display methods and software support. Then there comes the "measuring amplifier". Is that instrument necessary or does it play part in improving signal conditions? Would the compact amplifiers be an "out of the box", general purpose signal reading system while the measuring interfaces would be more suited for industrial gauging systems (reading the operation manuals slightly helps)?

OD measurement: Lastly, provided that I have this equipment, how would I use the LVDT's output for precision measurement of OD's (I'd imagine that ID's are best measured with plug gauges, in situ machined or purchased)? Optical comparison and bench micrometers are out of the question; costs, and the work piece must stay on the chuck. So far, it seems that one of the best methods is through comparison with gauge blocks. As described in the previous thread, I could set up a hand held stand with a flat surface and an actuated head holding the plunger perpendicular to the surface (like a horizontal height gauge). With gauge blocks, an initial reading is obtained with which the diameter of the part can be compared. Do setups like this exist and what are they called, or would I need to machine the holder myself? Furthermore, could this be used in place of a precision digital micrometer?

I acknowledge that I am indeed very new to metrology.

Regards,
Mr. Haelscheir

Indeed, I had originally overlooked that article when I first came upon it. Now that I am more familiar with the equipment involved, I remain at a loss between the various brands offered. I'd generally figure that I'd be trying to minimize given values in repeatability, sensitivity deviation, linearity deviation and hysteresis for reasonable compromises in cost or throw.

The fundamental idea is to have signal conditioning electronics demodulate the secondary coil voltage waveform into a bipolar DC signal. These signal conditioners could be built into the sensor, as with DC LVDTs, exist as a separate unit that connects directly to a readout's digital input or as integrated within the display unit itself. "Compact" amplifiers do tend to be standalone while "interfaces" general have larger input capacity and require/offer PC connection. The Mahr "interfaces" support modular jacks for various input types, one for direct inductive probe connection, air gauges or digital input respectively. The digital input jack is where I suspect that an external amplifying unit is necessary.

In those regards, I'll be contacting manufacturers for quotes and additional information. Any comments on my described OD measurement setup's feasibility? If this forum isn't so keen on LVDT measurement, is there any place you could direct me to?

Regards,
Mr. Haelscheir

After some research, it looks like what I am looking for is called an adjustable "snap indicator gauge" which basically follows the operating procedures I described. The idea is that I want to be able to mount the LVDT to act as an anvil and use gauge blocks to provide a reference for comparison. An LVDT snap gauge may never live up to a dedicated bench stand, though. Otherwise, I may find advantage in looking for metrology books focused on electronic gauging.

Could anyone familiar with snap gauges and comparative gauging chime in? Perhaps recommend gauges that accept LVDT sensors? Metro seems to be a promising manufacturer and one of the few offering the LVDT mounting facility. It would be great to use the same sensor and display unit for my TIR inspection requirements. Their setup may also help postpone the purchase of the micrometer I will be using for watchmaking work.

I hope this makes clearer what I'm looking for.

Regards,
Mr. Haelscheir

Mr. Haelscheir said:

After some research, it looks like what I am looking for is called an adjustable "snap indicator gauge" which basically follows the operating procedures I described. The idea is that I want to be able to mount the LVDT to act as an anvil and use gauge blocks to provide a reference for comparison. An LVDT snap gauge may never live up to a dedicated bench stand, though. Otherwise, I may find advantage in looking for metrology books focused on electronic gauging.

Could anyone familiar with snap gauges and comparative gauging chime in? Perhaps recommend gauges that accept LVDT sensors? Metro seems to be a promising manufacturer and one of the few offering the LVDT mounting facility. It would be great to use the same sensor and display unit for my TIR inspection requirements. Their setup may also help postpone the purchase of the micrometer I will be using for watchmaking work.

I hope this makes clearer what I'm looking for.

Regards,
Mr. Haelscheir

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Not sure how or what you researched.

Any of the links given here new to you?

Google

Google

@Gordon B. Clarke If it's necessary to state my sources, yes, I do tend to do extensive "tab-surfing" on Google. I gleaned information from a variety of links and search keys, including what you have linked. But yes, this is what I am looking at, plus a corresponding sensor and their display unit which accepts Metro, Mahr and TESA sensors etc. The snap gauge takes an 8 mm bore.

Mr. Haelscheir said:

@Gordon B. Clarke If it's necessary to state my sources, yes, I do tend to do extensive "tab-surfing" on Google. I gleaned information from a variety of links and search keys, including what you have linked. But yes, this is what I am looking at, plus a corresponding sensor and their display unit which accepts Metro, Mahr and TESA sensors etc. The snap gauge takes an 8 mm bore.

Click to expand...

Not sure if my reply should be written as a PM or in this post. Here goes.

I don't see that what you want is unusual but you write as if it is. if you know anyone that measures daily (that can be both a machinist and/or a technician) and take an informal chat with him/them I'm sure you can be more than nudged in the right direction.

If a picture is worth a 1,000 words then physically touching something is even better.

Gordon B. Clarke said:

Not sure if my reply should be written as a PM or in this post. Here goes.

I don't see that what you want is unusual but you write as if it is. if you know anyone that measures daily (that can be both a machinist and/or a technician) and take an informal chat with him/them I'm sure you can be more than nudged in the right direction.

If a picture is worth a 1,000 words then physically touching something is even better.

Click to expand...

Well, it seemed like an "exotic" means of measurement for as long as I had no idea that snap gauges were a thing. I make a hypothesis about my needs first while in a state of ignorance, then I determine whether a device exists that already fulfills them. The supposition is that these provide more reliable and precise measurements compared even to digital micrometers but with a measuring range situated around select gauge block references alongside environmental requirements. I'd like to hold it steady with a sensitive swing arm.

I don't know any machinists aside from the owner of the local tool store who sells and is fond of the "X lathes". He knows that Mitutoyu makes snap indicator gauges, but he isn't familiar with LVDTs. This is why I'd like to "walk around campus" and try to talk with the mechanical engineering professors and shop operators.

Mr. Haelscheir said:

I don't know any machinists aside from the owner of the local tool store who sells and is fond of the "X lathes". He knows that Mitutoyu makes snap indicator gauges, but he isn't familiar with LVDTs. This is why I'd like to "walk around campus" and try to talk with the mechanical engineering professors and shop operators.

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My last attempt. Ontario is huge but unless you are situated "in the middle of nowhere" I suggest you take contact to some shops and companies within driving distance and ask if you may visit.

I doubt if "mechanical engineering professors" can help and I don't think campus "shop operators" are up-to-date with the latest.

If I were you I'd give serious thought as to why you aren't getting replies.

Bye and good luck.

Gordon B. Clarke said:

If I were you I'd give serious thought as to why you aren't getting replies.

Click to expand...

Gordon, he's never going to figure that out.