December 16, 2020
An LVDT is, spelled out, a Linear Variable Differential Transformer. The basic gist of a LVDT is that it’s a common type of electromechanical transducer that is capable of converting the rectilinear motion of the object it’s incorporated in – coupled mechanically into the object’s corresponding electrical signal.
What’s a transducer?
A transducer is “…often employed at the boundaries of automation, measurement, and control systems, where electrical signals are converted to and from other physical quantities (energy, force, torque, light, motion, position, etc.). The process of converting one form of energy to another is known as transduction.”
There are many different applications of transducers, but, the more common types include:
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Those transducers that include a degree of electromagnetic energy will, where applicable, benefit greatly from an appropriate magnetic shielding component. Circling back to the topic at hand, such transducing technologies include Linear Variable Differential Transformers.
MuShield does a lot of work for many customers in constructing and providing the appropriate high permeability magnetic shielding solutions for LVDT devices worldwide.
The long and short of what exactly an LVDT is has been beautifully outlined by industry resource, TE:
LVDT linear position sensors are readily available that can measure movements as small as a few millionths of an inch up to several inches, but are also capable of measuring positions up to ±30 inches (±0.762 meter). The transformer’s internal structure consists of a primary winding centered between a pair of identically wound secondary windings, symmetrically spaced about the primary. The coils are wound on a one-piece hollow form of thermally stable glass reinforced polymer, encapsulated against moisture, wrapped in a high permeability magnetic shield, and then secured in a cylindrical stainless steel housing. This coil assembly is usually the stationary element of the position sensor.
The moving element of an LVDT is a separate tubular armature of magnetically permeable material. This is called the core, which is free to move axially within the coil’s hollow bore, and mechanically coupled to the object whose position is being measured. This bore is typically large enough to provide substantial radial clearance between the core and bore, with no physical contact between it and the coil. In operation, the LVDT’s primary winding is energized by alternating current of appropriate amplitude and frequency, known as the primary excitation. The LVDT’s electrical output signal is the differential AC voltage between the two secondary windings, which varies with the axial position of the core within the LVDT coil. Usually this AC output voltage is converted by suitable electronic circuitry to high level DC voltage or current that is more convenient to use.
Although an LVDT is an electrical transformer, it requires AC power of an amplitude and frequency quite different from ordinary power lines to operate properly (typically 3 Vrms at 3 kHz). Supplying this excitation power for an LVDT is one of several functions of LVDT support electronics, which is also sometimes known as LVDT signal conditioning equipment. Other functions include converting the LVDT’s low level AC voltage output into high level DC signals that are more convenient to use, decoding directional information from the 180 degree output phase shift as an LVDT’s core moves through the null point, and providing an electrically adjustable output zero level. A variety of LVDT signal conditioning electronics is available, including chip-level and board-level products for OEM applications as well as modules and complete laboratory instruments for users.
And where electronics are in play, so too is the importance of high permeability magnetic shielding to reduce electromagnetic interference from device to device / application to application. OEMs (Original Equipment Manufacturers) and their team of design engineers have a lot to consider when it comes to the design and execution of the magnetic shielding component of their tool, piece, part, and/or device – LVDT’s are a prime example of this. The benefit of utilizing the services of MuShield is that, magnetic shielding is exactly what we do and what we focus on. So, whether you have a blueprint in place, or need help working up the right solution (or simply just don’t want to take this piece of the process on yourself), our inhouse team of engineers are here to get the task at hand completed.
By and large, those in the business of designing and manufacturing transducer are actively doing their best to protect the transducer in play from outside electromagnetic (EMI) and radio-frequency (RMI) disturbances, and, to achieve this, certain design considerations can reduce or prevent effects of both. Don’t chalk it up to chance, get it right the first time… LVDT’s are a solid piece of “what we do”, day in, and day out.
The benefits of working with us, are, as we like to call it, the MuShield Advantage, which is one of experience, knowledge and customer-centric practices. Our extensive engineering experience allows us to contribute to the design process if required. Our process can help determine which materials and manufacturing methods will be most efficient and of highest quality. If you’ve got questions, we’ve got answers.