Contrinex's 2-wire inductive sensors enhance safety on mobile crane stabiliser systems

The sensors ensure that stabiliser legs are fully retracted before the vehicle can be driven, preventing accidental drive‑away incidents and protecting both operators and equipment.

Application overview

Mobile cranes, telescopic handlers and similar lifting vehicles rely on extendable stabiliser legs to maintain stability during lifting operations. These hydraulic jacks widen the vehicle’s footprint, preventing tipping when handling heavy loads.

Before the vehicle can be moved, however, it is essential to verify that all stabilisers have been fully retracted. Manufacturers typically achieve this through:

• Cab indicators that alert the operator, or
• Interlocks that prevent the transmission from engaging until the system confirms safe retraction.

The customer’s original system used mechanical limit switches. Although functional, these devices introduced long‑term drawbacks:

• Wear and tear from repeated actuation
• Higher lifetime maintenance costs
• Susceptibility to contamination and environmental conditions

To improve reliability and reduce service requirements, the manufacturer sought a non‑contact sensing solution.

Sensor-based solution

Contrinex’s Classic 600 Series inductive sensors provided an ideal upgrade path. The customer selected normally closed, 2‑wire inductive sensors, installing one on each stabiliser cylinder to detect the presence or absence of a target at the fully retracted position.

Why not wire in series?

At first glance, wiring the sensors in series, mirroring the previous mechanical‑contact arrangement, seems logical. However, inductive sensors introduce a challenge: voltage drop across multiple devices in series can compromise performance.

Parallel wiring for logic control

To overcome this, the engineering team adopted a more robust approach:

• Each sensor is configured as normally closed
• All sensors are wired in parallel
• The resulting configuration creates a logical NAND condition

This means the system only confirms a safe to drive state when every sensor detects its target correctly. If even one stabiliser leg is not fully retracted, the circuit remains open and the vehicle cannot be moved.

Outcome

The switch to Contrinex inductive sensors delivers several operational advantages:

• Zero mechanical wear, thanks to non‑contact detection
• Improved long‑term reliability in harsh outdoor environments
• Reduced maintenance costs over the vehicle’s lifetime
• Enhanced safety, ensuring stabilisers are always verified before travel

For manufacturers of mobile lifting equipment, this approach offers a robust, modern alternative to mechanical limit switches. 

Click to download Contrinex’s Product Overview brochure to find out more.

www.plusautomation.co.uk