WE PROVIDE CUSTOM BUILT SOLUTIONS TO SATISFY OUR CUSTOMERS.
MINIATURE LVDT:
- Measuring ranges from ±0.25mm to ±75mm
- Small size
- mV/V output
- Core only, core + extension & sprung loaded options
- Environmentally Sealed to IP40
STANDARD LVDT:
- Measuring ranges from ±0.5mm to ±550mm
- Low cost, ideal for OEM applications
- Conditioned outputs available; 4-20mA, 0-5V, 0-10V, ±2.5V
- Core only, core + extension (plain or guided) & sprung loaded options
- Environmentally Sealed to IP54
INDUSTRIAL LVDT:
- Measuring ranges from ±0.5mm to ±550mm
- Heavy, rugged construction for demanding environments
- Conditioned outputs available; 4-20mA, 0-5V, 0-10V, ±2.5V
- Core + extension, sprung loaded & guided core with rod end bearing options
- Sealed to IP65 as standard, IP68 submersible version available
Pressurized, Custom Design & Systems
- Pressurized versions for hydraulic cylinder applications
- Materials suitable for sea-water & marine service
- Dimensions to suit specific application requirements
- Multi-channel, rack amplifier based systems
SELECTING YOUR REQUIRED LDVT:
1. Ease Of Installation
Our range of LVDT displacement transducers
are available with a variety of body fittings and core
assemblies. These include:-
a) Axial or radial cable exit
b) Core only
c) Plain core with extension rod
d) Guided core with extension rod
e) Sprung loaded core with extension rod
f) Guided core with extension and rod end bearings
2. Material
Most of our LVDT displacement transducers are
constructed in stainless steel. For special applications, other materials can be used on request.
3. Sealing
Some models offer standard sealing to IP65, but other ratings are available up to IP68 for full submersible use. Our custom-design service allows variations in the sealing of all models. Please consult our Sales Office.
4. Robust Construction
We offer different levels of construction to suit the application. The industrial series give a high level of protection for harsh industrial conditions, however, for projects which involve possible extreme mistreatment, we recommend use of the heavy industrial series.
5. Electrical Connection
The choice of standard connections include:-
Flying cable (standard length is 2 metres - longer lengths to order.) Types available - PVC, PTFE, Polyurethane and armoured cables. Connectors. Types available - Hirschmann, Military.
6. Measuring Range
Each series of model types offers a wide choice of measuring ranges. The range can be applied as a bidirectional measurement about the zero point i.e. ±5.0mm, as a unidirectional measurement i.e. a ±5.0mm becomes 0-10mm, or for improved linearity performance part of the full range may be used.
7. Linearity
Our definition of linearity is that the output curve over the quoted linear range will not deviate from a theoretical straight line drawn through zero by more than 0.5% of full stroke. Linearity can be improved by using a smaller part of the total measuring range.
8. Outputs
The standard LVDT displacement transducer provides an
A.C. output and need a supporting electronic unit to energise and condition the signal. Some models are available with internal electronic circuitry to give a DC in - DC out performance. A suitable DC supply is needed and the choice of outputs available are D.C. bipolar, 0-5V, 0-10V and 4-20mA.
9. Other Specifications To Be Considered:-
a). Temperature range. Standards are -30°C to +85°C and -30°C to 150°C For higher temperature ranges, please consult our Sales Office.
b). Frequency response. This is determined by the mechanical arrangement used, the frequency of the energising supply and the filtering characteristics of the conditioning system.
c). Weight. The mass of transducer, in particular the core assembly, can be important.
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HOW LVDT OPERATES:
The LVDT, Linear Variable Differential Transformer is a well established transducer design which has been used throughout many decades for the accurate measurement of displacement and within closed loops for the control of positioning. In its simplest form, the design consists of a cylindrical array of a primary and secondary windings with a separate cylindrical core which passes through the centre. (Fig A)
The primary windings (P) are energised with a constant amplitude A.C. supply at a frequency of 1 to 10 kHz. This produces an alternating magnetic field in the centre of the transducer which induces a signal into the secondary windings (S & S ) depending on the position of the core.
Movement of the core within this area causes the secondary signal to change (Fig B). As the two secondary windings are positioned and connected in a set arrangement (push-pull mode), when the core is positioned at the centre, a zero signal is derived.
Movement of the core from this point in either direction causes the signal to increase (Fig C). As the windings are wound in a particular precise manner, the signal output has a linear relationship with the actual mechanical movement of the core.
The secondary output signal is then processed by a phase-sensitive demodulator which is switched at the same frequency as the primary energizing supply. This results in a final output which, after rectification and filtering, gives D.C. or 4-20mA output proportional to the core movement and also indicates its direction, positive or negative from the central zero point (Fig D).
The distinct advantage of using an LVDT displacement transducer is that the moving core does not make
contact with other electrical components of the assembly, as with resistive types, as so offers high reliability and long life. Further, the core can be so aligned that an air gap exists around it, ideal for applications where minimum mechanical friction is required.
The LVDT design lends itself for easy modification to fulfill a whole range of different applications in both research and industry.
Some typical variations include:-
- Complete sealing for part or full submersion in liquids
and gases
- Heavy construction build for tough industrial areas
- Miniature and low cost models for price-conscious OEM usage
- Internal electronic circuitry eliminating the need for additional instrumentation
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