Spring-Loaded AC Linear Variable Differential Transformer for Industrial Position Monitoring

The GH-750 Series AC Spring-Loaded LVDT Position Sensor from Macro Sensors, distributed by Harold G. Schaevitz Industries (HGSI), provides highly accurate and repeatable linear position measurement in a rugged, industrial-grade package. Designed for both laboratory and factory environments, this Linear Variable Differential Transformer (LVDT) utilizes a non-contact electromagnetic sensing principle combined with a precision spring-loaded probe to deliver reliable displacement measurement across a wide range of applications.

The GH-750 Series is constructed entirely of stainless steel and features hermetically sealed internal components with coil sealing to IEC IP68 standards, ensuring protection against dust, moisture, and other environmental contaminants.

Available in measurement ranges from ±0.050 inches to ±2.00 inches, the GH-750 Series provides flexibility for both high-resolution measurement and larger displacement monitoring applications.

Spring-Loaded Probe Design

The GH-750 Series incorporates a spring-loaded probe shaft guided by precision sleeve bearings. This design ensures consistent contact with the measured surface while maintaining smooth and repeatable motion of the LVDT core.

Key advantages of the spring-loaded design include:

• Consistent contact force across the measurement range

• Simplified installation without external linkages

• Ability to accommodate minor misalignment or surface variation

• Reliable performance in both static and dynamic measurement conditions

The guided armature design ensures stable motion and contributes directly to the sensor’s excellent repeatability performance.

AC LVDT Operating Principle

The GH-750 operates as a traditional AC LVDT, requiring external signal conditioning to generate excitation and process the output signal.

Typical operating characteristics include:

• Excitation voltage: 3.0 Vrms nominal

• Excitation frequency: 400 Hz to 10 kHz

When AC excitation is applied to the primary winding, a magnetic field is generated that induces voltages in two secondary windings. These secondary windings are connected in opposition, producing a differential output that varies proportionally with the position of the movable core.

The external signal conditioner demodulates this signal and converts it into a usable DC output that represents both position magnitude and direction.

Non-Contact Measurement Advantages

A defining characteristic of LVDT technology is its non-contact measurement principle. There is no electrical contact between moving and stationary components within the sensor.

This provides several important benefits:

• Virtually unlimited mechanical life

• No wear-related signal degradation

• Stable performance over millions of cycles

• Minimal maintenance requirements

While the probe tip contacts the measured surface, the internal sensing mechanism remains completely non-contact, combining the advantages of physical tracking with long-term electromagnetic reliability.

Accuracy, Linearity, and Repeatability

The GH-750 Series delivers excellent measurement performance:

• Linearity: ±0.15% typical, ±0.25% maximum of full scale output

• Repeatability: 0.01% of full scale

• Hysteresis: 0.01% of full scale

Repeatability is particularly critical in position monitoring and dimensional measurement applications. The GH-750’s non-contact sensing and precision bearing design ensure that repeated measurements of the same position produce consistent and reliable results.

Environmental Durability and Construction

The GH-750 Series is engineered for operation in demanding environments:

• Stainless steel housing

• Hermetically sealed internal construction

• IP68 environmental sealing

The sensor is resistant to:

• Dust and particulate contamination

• Moisture and humidity

• Shock and vibration

• Wide temperature variations

Operating temperature ranges include:

• Standard: –65°F to +275°F (–54°C to +135°C)

• High-temperature option: up to +400°F (204°C)

This makes the GH-750 suitable for both industrial and laboratory environments.

Optional Air-Extend Configuration

While the standard GH-750 Series uses a spring-loaded probe, certain variants (GHRA models) offer an optional air-extend / spring-retract configuration.

In this configuration:

• Low-pressure air (10–30 psi) extends the probe

• An internal spring retracts the probe when air is removed

This option is useful for automated measurement systems where probe engagement must be precisely controlled. However, it is important to note that pneumatic actuation is optional and not present in standard GH-750 models.

Signal Conditioning and Output Options

Because the GH-750 is an AC LVDT, it requires an external signal conditioner to operate. The signal conditioner performs:

• AC excitation generation

• Signal amplification and demodulation

• Output scaling

Common output formats include:

• ±10 VDC

• 0–10 VDC

• 4–20 mA current loop

The choice of output depends on system requirements, including noise environment, cable length, and compatibility with control or data acquisition systems.

Measurement Performance Considerations

Repeatability

Repeatability is the most critical performance characteristic in many position measurement systems. It defines how consistently the sensor reproduces the same output for identical inputs.

Because the GH-750 uses non-contact sensing and precision mechanical guidance, it maintains repeatability across millions of cycles without degradation.

Resolution

The GH-750 offers effectively infinite resolution as an analog sensor. Practical resolution is limited only by signal conditioning electronics and system noise, not by the sensor itself.

Linearity

The high linearity of the GH-750 simplifies calibration and ensures predictable output across the full measurement range.

Typical Applications

The GH-750 Series is widely used in:

• Industrial machinery position monitoring

• Automated inspection and gauging systems

• Materials testing equipment

• Laboratory R&D applications

• Factory automation and motion control

Its combination of durability, accuracy, and flexibility makes it suitable for both continuous monitoring and precision measurement tasks.

Installation Considerations

Proper installation is important to achieve optimal performance:

• Align the sensor with the direction of motion

• Use shielded cable for electrical connections

• Avoid routing cables near noise sources

• Position the sensor so the nominal measurement falls near mid-stroke

The spring-loaded design helps compensate for minor alignment variations, simplifying installation compared to rigid measurement systems.

Summary

The GH-750 Series AC Spring-Loaded LVDT provides a reliable, high-performance solution for linear position measurement in industrial and laboratory applications. With its non-contact sensing technology, hermetically sealed construction, and excellent repeatability, it delivers consistent and accurate results even in demanding environments.

The availability of multiple measurement ranges, optional high-temperature versions, and configurable output options makes the GH-750 Series a versatile choice for engineers and system designers seeking dependable position feedback.