An AC excitation power supply is the invisible lifeline for LVDTs, resolvers, and many AC‑powered sensors. When that supply drifts, your position feedback drifts. When it distorts, your control loop hunts. Yet most engineers check the sensor first, not the power feeding it.
I have debugged positioning systems that jittered by half a millimeter, only to find the excitation voltage was 10% low. The sensor was fine; the supply was not. Fixing the root cause—a poorly regulated AC source—solved everything.
How Excitation Quality Affects Your Measurements
AC sensors work by comparing output voltage ratios to the excitation input. If the excitation amplitude changes, the output ratio stays the same, but many measurement systems assume a fixed excitation level. A 5% drop in excitation becomes a 5% error in reported position.
Amplitude stability is the first spec to check. A good AC excitation supply holds output voltage within ±0.5% over line, load, and temperature. Many low‑cost units drift 2–3% as they warm up, or sag 5% under full load. That sag directly translates into sensor error.
Total Harmonic Distortion (THD) is the second factor. An LVDT expects a clean sine wave. Harmonic content, especially third harmonic, shifts the zero crossing and changes the RMS value. A supply with 5% THD introduces position errors that vary with the sensor’s phase angle. For precision applications, THD should stay below 1%.
Frequency stability matters for sensor speed and phase response. A 5% frequency error changes the output voltage of an inductive sensor by roughly the same percentage. For a resolver used in a servo drive, that frequency shift also changes the phase relationship between the excitation and the output signals, potentially causing commutation faults.
Product Introduction: An Excitation Supply That Stays Stable
A purpose‑built AC excitation power supply is not the same as a general‑purpose function generator or a variable transformer. It needs specific features for industrial feedback sensors.
Output voltage range should cover common excitation levels: 2 V, 5 V, 7 V, and 10 V RMS, with fine adjustment via a multi‑turn potentiometer or digital command. The output should be isolated from ground to prevent ground loops in sensor wiring. Isolation voltage of 250 V or more protects the supply if a sensor lead shorts to a motor winding.
Frequency selection should include 400 Hz, 1 kHz, 3 kHz, and 5 kHz—the standard bands for LVDTs and resolvers. A switch or a remote command changes frequency without recalibrating the amplitude. Better units offer frequency tracking, where the supply locks its output to an external reference for multi‑axis systems that need synchronized excitation.
Load regulation matters because a single supply often powers multiple sensors. The supply must maintain voltage within spec from no load to full load. Look for a load regulation figure of 0.1% or better.
Protection features include short‑circuit and overcurrent shutdown, with automatic recovery after the fault clears. Thermal protection prevents damage if the supply runs at high ambient temperatures.
For automated test or production, remote control is essential. An analog input allows external programming of amplitude and frequency. A digital interface (RS‑232 or Ethernet) logs output voltage and current, and provides status flags for over‑temp, overload, and regulation failure.
When the excitation supply is stable, your sensors tell the truth. That stability is worth every dollar of the investment.
For more information, visit Jetronl’s website: https://www.jetronlinstrument.com/.