LVDT & RVDT amplifiers

Measuring amplifiers for LVDT and RVDT sensors

LVDT and RVDT measuring amplifiers are used to excite and evaluate inductive displacement and rotary position sensors. LVDT sensors (Linear Variable Differential Transformer) measure linear movements and positions, while RVDT sensors (Rotary Variable Differential Transformer) are used for non-contact measurement of angular positions.

Both sensor types operate according to the inductive differential transformer principle and require an AC voltage for excitation. The measuring amplifier generates this excitation voltage, evaluates the AC signal returned by the sensor and converts it into a standardised analogue signal for further processing.

Depending on the version, Althen LVDT and RVDT amplifiers are available with 0–10 V, ±10 V, ±5 V or 4–20 mA outputs. Zero point and gain can be adjusted to the sensor and measuring range. Various models also allow multiple amplifiers to be synchronised to prevent mutual interference in multi-channel applications.

For different installation requirements, compact DIN rail modules, rugged amplifiers in EMC aluminium housings with protection ratings up to IP66, and single- and dual-channel 19-inch rack modules are available.

Precise signal conditioning for displacement and angular position measurements

Althen LVDT and RVDT measuring amplifiers combine stable sensor excitation with precise signal evaluation and flexible standard outputs. This allows inductive position sensors to be easily integrated into industrial control and measurement systems.

What to consider when selecting an LVDT or RVDT measuring amplifier

1. Determine whether an LVDT or RVDT is used
First, the sensor type must be determined. LVDTs measure linear displacement or travel, while RVDTs measure angular displacement or rotary position.

Depending on the version, Althen measuring amplifiers can be used with both sensor types.

2. Consider excitation voltage and oscillator frequency
LVDT and RVDT sensors require an AC voltage at a specific frequency. The measuring amplifier and sensor must therefore be matched in terms of excitation voltage and frequency.

Various Althen amplifiers, for example, are available with oscillator frequencies of 4.8 kHz or 10 kHz. Other versions operate at 3.5 kHz. Customer-specific frequencies are also possible depending on the device.

3. Consider sensor sensitivity and gain
The output signal of an LVDT or RVDT depends, among other factors, on the sensor sensitivity and measuring range. The amplifier must therefore be adjustable accordingly.

On various devices, coarse gain can be set using DIP switches. Zero point and full-scale value can also be adjusted using potentiometers.

4. Select the appropriate output signal
The output signal should match the downstream evaluation electronics.

Typical options include:

• 0–10 V
• ±10 V
• ±5 V
• 4–20 mA

A bipolar output signal such as ±10 V is particularly suitable when movements in both directions around an electrical zero point need to be represented.

5. Determine single- or multi-channel operation
Compact single-channel amplifiers are available for individual displacement or angular measurement points. If several sensors are used, dual- or multi-channel solutions or several synchronised amplifiers can be used.

For 19-inch systems, single- and dual-channel rack modules are available, for example. Rugged dual-channel devices for industrial applications are also available.

6. Consider synchronisation of multiple amplifiers
If several LVDT or RVDT measuring amplifiers are operated in close proximity, different oscillator frequencies can cause mutual interference.

With suitable devices, the oscillator signals can therefore be synchronised between master and slave amplifiers. This is particularly important in multi-channel measurement systems.

7. Check galvanic isolation
In industrial measurement systems, potential differences and ground loops can affect signal quality. Galvanic isolation between the power supply and analogue output or sensor excitation can reduce these sources of interference.

Various Althen amplifiers in DIN rail and IP-rated housings provide corresponding galvanic isolation.

8. Select the design and protection rating
The installation location largely determines the required design.

Compact DIN rail amplifiers are suitable for installation in control cabinets. For harsh industrial environments, amplifiers in protected aluminium housings with IP65 or IP66 ratings are available. For test benches and larger measurement systems, 19-inch plug-in modules can be used.

9. Consider dynamic performance requirements
For rapid position changes, the bandwidth of the measuring amplifier must be sufficiently high. The cut-off frequency depends, among other factors, on the oscillator frequency used.

Static positioning tasks therefore have different requirements than dynamic displacement or angular measurements in test benches and machines.

10. Plan the calibration of sensor and amplifier
The sensor and measuring amplifier together form a measurement chain. For precise results, zero point and gain should be adjusted to the sensor used and the actual measuring range.

Depending on the application, factory calibration of the complete measurement chain may be beneficial.

Our technical expert team will be happy to support you in matching the LVDT or RVDT sensor, excitation frequency, amplifier, output signal and installation situation. Contact our sales team

Typical applications for LVDT and RVDT measuring amplifiers

LVDT and RVDT measuring amplifiers are used wherever linear positions or angular displacements need to be measured precisely with inductive sensors and further processed as a standardised signal.

Typical applications include:

• Industrial displacement and position measurement
• Angular and position measurement
• Machine and plant engineering
• Automation technology
• Process monitoring
• Test benches and test systems
• Component and material testing
• Quality control
• Machine tools
• Valve and damper position measurement
• Actuator monitoring
• Hydraulic and pneumatic systems
• Measurement of deformation and displacement
• Laboratory and testing applications
• Research and development
• Automotive engineering
• Aerospace
• Shipbuilding
• Railway technology

Thanks to different channel configurations, output signals, designs and protection ratings, the amplifiers can be used both for individual measuring points and industrial multi-channel measurement systems.