LVDT Manufacturers in India — and When a Potentiometric Transducer Is the Better Buy

A lot of linear position enquiries in India arrive asking for an LVDT. Often the application genuinely needs one. Just as often the buyer is asking for an LVDT because that is the technology they encountered first, and a potentiometric or Hall-effect transducer would do the job for less money, with shorter lead times and easier support.

This is a comparison of the three technologies from a purchasing point of view rather than a physics one, so that the enquiry you send matches the problem you have.

LVDT: what it is genuinely good at

A linear variable differential transformer measures displacement through electromagnetic coupling between a primary coil and two secondary coils, with a movable core. Because the core does not touch the coils, there is no wear in the measuring path.

Its real strengths are narrow and worth respecting:

• Very high resolution over short strokes. Sub-micron measurement is achievable. For metrology, materials testing and precision gauging, nothing else is as appropriate.
• Effectively infinite mechanical life in the measuring path.
• Excellent repeatability in a controlled environment.

The costs are equally specific. An LVDT needs AC excitation and signal conditioning electronics, so the installed cost is well above the sensor price. Strokes are typically short. And the whole assembly is more expensive than the alternatives by a margin that is difficult to justify unless you are actually using the resolution.

Potentiometric: the workhorse

A potentiometric transducer is a precision resistive track with a wiper. Apply a voltage across the track and the wiper delivers a voltage proportional to position. It is the simplest possible arrangement and it remains the correct answer for a large share of industrial stroke measurement.

• Direct DC output with no conditioning electronics required
• Absolute by nature — position is known at power-up with no homing
• Long strokes available, well past what LVDTs practically cover
• Substantially lower installed cost

The trade-off is the wiper. It is a contacting device, so in very high-cycle applications the track eventually wears. In practice, for machine positioning, hydraulic cylinder feedback, valve position and press ram measurement, this is rarely the limiting factor — and Novotechnik conductive plastic elements are considerably more durable than the wirewound potentiometers the objection usually has in mind.

The Novotechnik potentiometric range we supply covers a wide span of formats: TLH side-actuated, LWH, LWG and LWX, the TR and TRS spring-return units, TEX in rod and pivot-head mountings, TE1, TX2, and the PTX sensor kit for integration into a customer housing.

Hall-effect and touchless: the modern middle ground

Magnetic touchless transducers give you the wear-free measuring path of an LVDT without the excitation and conditioning overhead. There is no contact, the output can be a straightforward analogue signal or a digital bus, and protection ratings can be very high because nothing has to penetrate the housing.

For high-cycle industrial applications that do not need sub-micron resolution, this is frequently the correct modern answer, and it is where a lot of applications that would once have used an LVDT now sit.

Choosing between them

Specify an LVDT when you need sub-micron resolution over a short stroke, in metrology, materials testing or precision gauging — and when you have budgeted for the signal conditioning.

Specify potentiometric for general machine positioning, cylinder feedback, valve position and press applications, where you need a reliable absolute reading, a simple DC output and a sensible price. This covers most industrial enquiries.

Specify touchless when cycle counts are high, the environment is hostile, washdown is involved, or you want the position on a fieldbus.

On sourcing LVDTs in India specifically

Worth being direct: we do not manufacture LVDTs, and we would rather say so than sell you something adjacent and call it equivalent. What we do supply is the full Novotechnik linear position transducer range as sole authorised distributor for India and SAARC, covering potentiometric and touchless technologies across a wide range of strokes and mountings.

If your application genuinely requires an LVDT, tell us and we will say so. If it does not — and in our experience most do not — we can usually offer a transducer that is available faster, costs less installed, and needs no signal conditioning.

What to send us

• Stroke length required, and the mechanical space available
• Resolution and accuracy genuinely needed, as a number rather than as high
• Expected cycles per day and the intended service life
• Output required and the controller it feeds
• Environment: temperature, protection rating, washdown, vibration
• Mounting arrangement, and whether a return spring is needed

Our guide to selecting a linear position transducer covers the mechanical decisions in more detail.