A manufacturer of mobile cranes uses inductive sensors to detect the position of stabilizer legs as part of the vehicle safety system. Before the system will allow the driver to drive the vehicle away, sensors confirm that stabilizer legs have been retracted.
- No readjustment over time
- No wear and tear
- Relatively tamper proof
- Long term reliability
- No maintenance
- Easy adjustment/setup
- Local annunciation (LED)
Mobile cranes, bucket trucks, ladder trucks and the like are equipped with extendable stabilizer legs that prevent the vehicle from tipping over during stationary operation with an overhanging load. These stabilizer legs (or jacks) are mechanical extensions of the chassis that essentially widen the base of the vehicle to ensure its stability in all operating situations. However, when the time comes to move the vehicle, there must be verification that these stabilizers are retracted. Either an indicator in the driver’s cab or a method of disabling engagement of the vehicle’s transmission is utilized to promote 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. A non-contact solution is therefore sought.
A normally closed, two-wire inductive sensor from the Classics family (Special range) is suitable for this application. Multiple sensors (one for each stabilizer 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 a non-contact, non-mechanical approach to providing feedback for the warning or inhibiting mechanism of the vehicle.