How does inductive position sensing work?

An inductive position sensor uses a series of coils to measure the position of a metallic target called an activator. The coil generates a magnetic field, the activator responds with its own opposing field, and the sensor compares that induced field across the coil series to calculate absolute position. Sensor and target never touch, so there is no wear and no mechanical life limit.

The three-step cycle

The measurement is not continuous excitation. It is a repeating cycle of three steps, and understanding it explains most of the advantages.

• Generate. The coil generates a magnetic field which penetrates the activator, causing the activator to produce its own opposing field.
• Respond. The coil stops generating, and measures the field the activator has induced.
• Compare. That measurement is compared across the series of coils, which gives an absolute position for the activator rather than a relative one.

Absolute matters. The sensor knows where the activator is at power-on, with no homing move and no reference run, which is what lets it be used on something that cannot safely be moved to find its own datum.

The activator is your part, not ours

The moving half of the system is a metallic target, typically mild steel, mounted to or machined into the moving part of the application. It carries no electronics, no magnet and no wiring.

For an OEM that is the useful bit. The activator can be an existing part of the assembly, machined into it at manufacture, or a separate component profiled to shape the output curve. Standard activator designs are published in the Blade technical manual for the 25 mm and 60 mm linear sensors and for the rotary.

What the principle buys

• Non-contact, so long-term reliability in harsh environments, with no mechanical linkage to wear.
• Fully sealed designs for temporary immersion (1 m for 30 min), IP67 across the range.
• No output drift with temperature change.
• Linear, angular, rotary and non-uniform measurement, from around 20 mm to 100 mm and beyond.
• Unaffected by permanent magnets or the Earth’s magnetic field.
• Wide operating temperature range, with the signal processing electronics not required to sit at the sensing point.
• A constant air gap between sensor and activator, so nothing deteriorates through use.

The range, and configuring it

Configuration runs through the BladeCom tool: minimum and maximum travel set points, open and closed switch points, top and bottom output limits, dropout level, write protection and a live graph. The 25 mm and 60 mm sensors connect over RS232 and the rotary over RS485.

The sensors report their own health: sensor fault, whether the activator is in range, approximate temperature and environmental health. That turns the position sensor into a condition-monitoring point for the installation around it, which is worth wiring into the host system rather than ignoring.