Drift in winding resistance readings can confuse diagnosis — here are the most common causes and how to check each.
📖 Understanding why drift occurs starts with understanding how a winding resistance meter works — particularly the 4-wire Kelvin measurement method and stabilisation time. Our Complete Guide covers both in detail.
Temperature Variation
Resistance of copper changes with temperature. Even small ambient or winding temperature differences can produce noticeable drift unless readings are corrected to a reference temperature.
Poor Kelvin Connections
Dirty, loose or corroded Kelvin clamps introduce variable contact resistance. Always clean contact surfaces and ensure firm mechanical pressure.
Lead Heating & Measurement Current
Using excessive test current or leaving current applied for long periods can heat leads and windings, causing drift as temperatures rise.
Residual Magnetism / Core Effects
Residual magnetism in the core can cause slow settling and small DC offsets — demagnetize if required and allow sufficient stabilization time.
Instrument Stability & Calibration
An uncalibrated or faulty meter may show drift. Verify the meter against a known reference and ensure batteries/supplies are stable.
Loose Tap Changer Contacts
Intermittent tap contacts create fluctuating resistance as the contact resistance changes with small movements or temperature.
How to Diagnose Drift (Quick Checklist)
- Check and clean Kelvin contacts.
- Measure ambient and winding temperature and apply correction.
- Use a stable, recommended DC test current and wait for stabilization.
- Repeat reading after a short rest and compare results.
- Use a second meter as cross-check if needed.
Addressing these root causes will typically eliminate drift and result in repeatable, trustworthy measurements.