Does a magnetic scale have power-off retention?

Whether a magnetic scale (magnetic encoder) retains its position after power loss depends on its type:

--Absolute magnetic scale: Yes, it retains position upon power loss. Each position corresponds to a unique code, so the system “remembers” the position even if powered off.

--Incremental magnetic scale: No, it does not retain position after power loss. It only outputs relative movement signals, so it loses its reference when power is cut and requires homing or re-zeroing on restart.

In short: Absolute = retains position; Incremental = does not retain position.

1. Basic Types and Working Principle of Magnetic Scales

A magnetic scale is a sensor used for precise displacement measurement, consisting of a magnetic ruler (scale) and a magnetic read head:

--Magnetic Ruler:A magnetic thin film is deposited on a non-ferromagnetic substrate, forming periodic magnetization signals (alternating magnetic poles).

--Magnetic Read Head:Contains sensing elements (Hall sensors or magnetoresistive elements) that detect changes in the magnetic field and convert them into electrical signals.

Working Principle:
When the read head moves relative to the magnetic ruler, the sensing elements detect the magnetic field variations. These changes are converted into electrical signals, which are then processed to calculate the displacement.

2. Incremental vs. Absolute Magnetic Scales: Power-Off Behavior Differences

1. Incremental Magnetic Scale: No Power-Off Retention

--Measures relative displacement via counting pulses; no absolute position encoding.

--After power loss: position information is lost; recalibration or homing is required for normal operation.

--On restart, the system “forgets” the previous position and must re-establish a reference point.

2. Absolute Magnetic Scale: Power-Off Retention

--Each position has a unique code (e.g., a 13-bit pseudo-random binary sequence).

--After power loss: the magnetization pattern on the scale remains intact; position information is retained.

--On restart, the system can directly read the absolute position without calibration.

3. Technical Principle Behind Power-Off Retention

The key to absolute magnetic scales retaining position lies in their coding method:

--Absolute Code Track: In addition to incremental tracks, the magnetic ruler has absolute code tracks, where each position has a unique magnetic field orientation.

--Power-On Recovery: Upon system restart, the absolute code track is read first to determine the current position, enabling calculation of the precise coordinate.

--Physical Basis: Magnetic signals rely on the remanence property of the magnetic material. High-quality magnetic scales can stably preserve signals for 10+ years.

4. Application Scenarios Comparison

Summary:

-- Incremental magnetic scales are cost-effective and suitable for systems with continuous power and reference homing.

-- Absolute magnetic scales are essential where position retention after power loss is critical, ensuring continuous operation and high reliability in high-end industrial applications.

5. Summary

Power-off retention in magnetic scales is not universal—it depends on the type:

-- Absolute Magnetic Scale: Retains position after power loss. Position information is preserved, making it suitable for precision applications requiring continuous position tracking.

-- Incremental Magnetic Scale: Does not retain position after power loss. Position is lost upon shutdown and requires recalibration, suitable for cost-sensitive applications where periodic homing is acceptable.

Selection Recommendation:

-- If your application requires accurate position knowledge after power loss (e.g., elevators, precision machining equipment), choose an absolute magnetic scale.

-- If cost is a priority and occasional recalibration on restart is acceptable, an incremental magnetic scale is more economical.