LVDT Sensors
The LVDT sensors They are inductive transducers used to measure linear displacement and position They are used continuously, accurately, and repeatably in industrial machinery, test benches, automation, actuators and valves, metrology, hydraulic systems, structural monitoring, and numerous position control applications.
At GUEMISA we have different LVDT configurations depending on the travel, geometry, electronics and signal required: Amplified LVDTs with industrial output, AC or unamplified LVDTs, half-bridge LVDTs, angle transducers, and signal conditioners.
Quick selection by sensor type:
- amplified LVDTs: models with integrated electronics and industrial signals such as 4-20 mA, 0-10 V or ±10 V depending on the series.
- Unamplified LVDT / AC: transducers that require external excitation and conditioning electronics.
- LVDT angles: inductive solutions for measuring position or angular displacement.
- LVDT Conditioners and Converters: electronics to power, demodulate and convert the sensor signal into formats usable by PLCs, acquisition systems or controllers.
How to choose an LVDT sensor
To select the correct LVDT, it is not enough to define the stroke. The electrical architecture, core type, required signal, available space, temperature, pressure, environmental protection, and the system to which the sensor will be connected must also be considered.
The following sections summarize the main technical criteria. For exact wiring, power supply, pinout, or compatibility information for each part, please refer to the corresponding product datasheet and FAQs.
What is an LVDT sensor and how does it work?
LVDT comes from Linear Variable Differential Transformer or linear variable differential transformer. It is an inductive transducer in which the movement of a ferromagnetic core modifies the magnetic coupling of the coils and allows obtaining an electrical signal related to position.
In a classic differential LVDT, there is an excitation and a differential signal that varies in amplitude and phase depending on the core's position. When passing through the electrical zero position or null, The relationship between the signals changes sign and allows us to determine both the magnitude and the direction of the displacement.
Within industrial LVDT transducers, there are different electrical architectures. In addition to full-bridge differential configurations, there are inductive half-bridge LVDT. In these models the coil configuration and conditioning electronics are different, so a conditioner compatible with the sensor must be used.
Several families from Schreiber Messtechnik, For example, they use half-bridge LVDT technology.
If you would like to learn more about the electromagnetic principle, please consult our technical guide. What is an LVDT sensor and how does it work?.
Types of LVDTs: amplified, unamplified, AC, DC, and half-bridge
One of the most important decisions is determining where the signal conditioning will be performed.
| Configuration | Electronics | Usual signal | When to use it |
|---|---|---|---|
| LVDT AC / unamplified | External | AC signal from the transducer | When it is desired to separate the electronics from the point of measurement, reduce size, or work under demanding conditions. |
| Amplified LVDT / DC | Integrated | 4-20 mA, 0-10 V, ±10 V or others depending on the model | When you are looking for easy integration with PLC, data acquisition or control systems. |
| half-bridge LVDT | Typically compatible external conditioner or specific electronics | Arousal and conditioner dependent | Industrial applications where compact inductive transducers and dedicated electronics are used. |
| angular LVDT | Integrated or external depending on the series | Analog or inductive signal | Continuous measurement of position or angular displacement. |
You can consult the amplified LVDTs and the Unamplified LVDT.
Criteria for correctly selecting an LVDT
- Route or race: It must cover the entire movement of the application while remaining within the useful and linear range specified by the manufacturer.
- Linearity and precision: They should be chosen based on the acceptable uncertainty of the entire system, not just the nominal resolution of the sensor.
- Signal type: Consider whether you need an AC LVDT, a sensor with integrated electronics, or an industrial output such as 4-20 mA or 0-10 V.
- Electrical architecture: Check if it is a full bridge, half bridge, or other configuration and use compatible conditioning electronics.
- Mechanical configuration: free core, guided core, stem, spring-loaded probe, or other geometry depending on how the movement occurs.
- Environmental conditions: temperature, humidity, dust, immersion, pressure, vibration, chemicals and degree of protection required.
- Integration: available space, diameter, total length, fixings, threads, cable exit, connector and distance to the acquisition system.
If the LVDT replaces an existing sensor, its sensors should also be checked. mechanical dimensions, sensitivity, excitation frequency, travel, and current electronics before considering an equivalence.
Free core, guided core, or spring-loaded probe
The way in which the core moves relative to the sensor body determines the assembly and the mechanical life of the unit.
- Free nucleus: The core is attached directly to the moving element and travels without contact with the coils. This is appropriate when the machine itself ensures good alignment.
- Guided core: The movement is carried out by means of a rod or guided mechanism incorporated into the transducer, simplifying the mechanical installation.
- Spring-loaded probe: The tip remains in contact with the surface by means of a return spring. It is commonly used in metrology, dimensional control, and test benches.
There is no universally best configuration: the choice depends on the actual movement, available alignment, speed, and allowable forces on the measured part.
Industrial applications of LVDT sensors
LVDT technology is used when it is necessary to obtain a continuous measurement of displacement or position with good repeatability and a long service life.
- Position control in industrial machinery and automation.
- Presses, testing machines and test benches.
- Control of actuators and valves.
- Positioning in hydraulic and pneumatic systems.
- Displacement control in turbines and energy equipment.
- Metrology, inspection and dimensional control.
- Measurement of deformations and displacements in materials testing.
- Structural monitoring and civil works.
- Research and development teams.
- OEM systems integrated into machinery and measuring equipment.
The working environment is crucial: a model suitable for a test bench may not be appropriate for a steam valve, a hydraulic cylinder, or an outdoor installation.
LVDT miniature, IP68, high pressure and high temperature
In addition to standard industrial models, there are LVDTs developed for specific mounting conditions and restrictions.
- LVDT thumbnail: They reduce the diameter and mass of the assembly for installations with very little available space.
- LVDT IP67/IP68 or submersible: intended for humidity, weathering, immersion or other environments where watertightness is critical.
- LVDT for high pressure: used in hydraulic systems, cylinders, actuators and other assemblies where the transducer may be exposed to pressurized fluids.
- LVDT for high temperature: They frequently separate the sensor element from the electronics to keep the electronic components away from the hot zone.
- LVDT for vibration or severe environments: They require a mechanical construction, wiring and fastening system suitable for the actual operating conditions.
These designations do not replace checking the technical data sheet: the actual limits of temperature, pressure, immersion, shock or vibration depend on each series and reference.
Advantages of LVDT compared to other displacement technologies
One of the main advantages of the LVDT is that the measurement is obtained using an inductive principle. In free-core configurations, there is no electrical contact between the moving element and the windings, which allows for a long service life and good repeatability.
Facing a linear potentiometer, An LVDT prevents electrical contact with a resistive track and is particularly useful when many operating cycles are expected.
The magnetostrictive sensors, Laser, potentiometric, and other displacement technologies may be more appropriate for certain applications. The choice should be made based on stroke, accuracy, speed, environment, space, cost, and signal type, not solely on the sensor technology.
Frequently asked questions about LVDT sensors
What is the difference between an amplified and an unamplified LVDT?
An unamplified LVDT requires external electronics to provide excitation and signal conditioning. An amplified LVDT incorporates this electronics into the transducer or assembly itself and can directly deliver industrial signals such as 4-20 mA or 0-10 V, depending on the model.
Can an LVDT be connected directly to a PLC?
It depends on the model. An AC or passive LVDT typically requires a signal conditioner. A model with integrated electronics and a compatible output, such as 4-20 mA or 0-10 V, can be connected to the corresponding analog input of the PLC. The exact wiring should be checked on the datasheet for each model.
What is a half-bridge LVDT?
It is an inductive configuration in which the transducer uses a half-bridge architecture and requires compatible electronics for its excitation, demodulation, and conditioning. It should not be assumed that any LVDT conditioner is compatible with any half-bridge sensor.
Does an LVDT have infinite resolution?
The inductive principle provides a continuous signal and is not limited by discrete measurement steps. In a real-world installation, the achievable resolution is conditioned by the signal conditioner, electrical noise, data acquisition, mechanical stability, and the rest of the measurement system.
What information do I need to replace an old or discontinued LVDT?
Whenever possible, it's advisable to have the manufacturer and part number, technical data sheet, or a photograph of the label. Also important are the stroke, body dimensions, core type, mechanical connection, number of wires, power supply or excitation frequency, sensitivity, output signal, and environmental conditions.
What information does Guemisa need to recommend an LVDT?
At a minimum, you will need to provide: the distance to be measured, the available space, the type of mounting, the desired signal, the system to which the sensor will be connected, and the environmental conditions. If it's a replacement, a photograph and the part number of the existing sensor usually speed up the search for an alternative considerably.
Selection, equivalencies and replacement of LVDT sensors
GUEMISA can help in the Selection of LVDT sensors, signal conditioners, and replacement of existing references. When a model is discontinued or has a long delivery time, we can study alternatives based on their electrical and mechanical characteristics.
To study an application or equivalency, send us the Existing brand and reference, technical data sheet or photograph of the sensor, along with the race, starting signal, dimensions and available operating conditions.