Short Answer
Both AC and DC LVDTs are contactless, inductive linear position sensors based on the same core transformer principle. The key difference is how the signal is handled:
- AC LVDTs output a raw AC signal and require external signal conditioning
- DC LVDTs include built-in electronics and provide a direct DC output
How Do Their Outputs Differ?
An AC LVDT produces a differential AC signal from its secondary coils. This signal:
- Requires an AC excitation source
- Must be demodulated and conditioned using an AC LVDT Signal Conditioner to produce a usable DC output
A DC LVDT performs these steps internally. It:
- Excites the sensor
- Demodulates the signal
- Outputs a scaled DC signal such as 0–5 V, 0–10 V, or 4–20 mA
From a system perspective, a DC LVDT behaves more like a standard analog sensor.
What About Signal Conditioning?
- AC LVDT:
- Requires an external AC LVDT signal conditioner
- Greater flexibility in tuning gain, filtering, and scaling
- More components in the measurement chain
- DC LVDT:
- Signal conditioning is integrated into the sensor
- No external electronics required
- Simplifies wiring and setup
How Do They Compare in Installation?
AC LVDTs require additional setup:
- Separate conditioner must be mounted and powered
- Additional wiring between sensor and electronics
- Configuration of excitation and output scaling
DC LVDTs are generally easier to install:
- Fewer components
- Direct connection to PLCs or DAQ systems
- Reduced wiring complexity
Are There Performance Differences?
Both types provide:
- High resolution and repeatability
- Frictionless, contactless operation
- Long service life
However:
- AC LVDTs allow for external optimization of signal conditioning, which can be beneficial in high-precision or specialized measurement systems
- DC LVDTs offer consistent, factory-calibrated performance with minimal setup
What About Environmental Considerations?
This is one of the most important differences.
- AC LVDTs:
- Can keep electronics remote from heat, vibration, or contamination by using a separate signal conditioner
- DC LVDTs:
- Contain electronics within the sensor body
- Must be used within the temperature and environmental limits of those electronics
When Should I Choose an AC LVDT?
An AC LVDT is often preferred when:
- The environment is too harsh for integrated electronics
- You need flexible or custom signal conditioning
- The system already includes external LVDT signal conditioning hardware
When Should I Choose a DC LVDT?
A DC LVDT is typically the better choice when you need:
- A plug-and-play solution
- A direct analog output for control systems
- Minimal wiring and fast installation
Bottom Line
Both AC and DC LVDTs use the same sensing principle, but differ in how the signal is delivered:
- AC LVDT → External conditioning required, more flexible, better for extreme environments
- DC LVDT → Integrated electronics, direct DC output, simpler integration
Choosing between them depends on your system design, environmental conditions, and how much flexibility or simplicity your application requires.