Mobile cranes trust Contrinex inductive sensors to ensure they’ve tucked their legs in

A manufacturer of mobile cranes uses Contrinex 2-wire inductive sensors, available from PLUS Automation, to detect the position of stabiliser legs as part of the vehicle safety system. Before the system will allow the driver to drive the vehicle away, sensors confirm that stabiliser legs have been retracted.

Mobile cranes, telescopic handlers and the like are equipped with extendable stabiliser legs to prevent them from tipping over when lifting. These stabiliser legs (or jacks) are mechanical extensions of the chassis which widen the base of the vehicle’s chassis to ensure its stability in all operating situations. However, when the time comes to move the vehicle, there must be verification that these stabilisers are fully retracted. Either an indicator in the driver’s cab or a method of disabling engagement of the vehicle’s transmission is used to ensure safety and prevent drive-away accidents and damage.

The customer’s existing verification system relies on mechanical contacts. However, the costs of maintenance and replacements over the long lifetime of such vehicles are relatively high and hence a non-contact solution was sought.

A normally closed, two-wire inductive sensor from Contrinex’s Classic 600 Series was ideal for this application. Multiple sensors (one for each stabiliser cylinder) are installed and connected in a way that requires each sensor to be satisfied that a target is either present or absent, thus completing a logic circuit.

Initially, the simplest approach would seem to be to wire this group of devices in series, as would be the case with mechanical contacts. However, when using sensors, series wiring presents the challenge of voltage drops. The customer overcomes this by selecting 2-wire sensors with a ‘normally closed’ output, then wiring them in parallel to create a logical NAND situation.

This wiring solution resolves the issue and permits an easy to implement, non-contact, non-mechanical approach to providing feedback for the warning or inhibiting mechanism of the vehicle.