During a lift, the Master controller is simply the first control box switched on. It scans the frequencies to determine it's the first, then asks the operator to input the number of columns that will be used. This lets the master calculate how many time slots or listening cycles to include after its own. It then starts broadcasting, with slaves broadcasting into empty slots they find when they are switched on. When control boxes are not sending data, they listen to the other units, so data is transmitted and received by all columns without wires or cables.

But dedicated inground lifts take up space, even when not in use, and leaking fluids can pollute the surrounding ground. Mobile lifts free up space, but the tangle of cords and cables creates hazards for technicians, makes it difficult to roll equipment under lifted vehicles, and causes excessive cable wear. An alternative, WPLS-160 Mobile Column Lifts made by Gray Professional Service Equipment, St. Joseph, Mo. (www.grayusa.com), uses wireless technology and dc power to eliminate cords and simplify the process.

Each lift can raise 8-ton loads 67 in., with one lift needed for each wheel on the vehicle, up to a total of six. Each lift weighs 1,360 lb and raises loads at 50 ipm. They are equipped with casters for mobility and a 12-V deep-cycle battery which powers a hydraulic system that actually does the lifting and lowering. A built-in battery charger plugs into any 110-V outlet.

To ensure the lifts work in unison and vehicles remain level at all times, Gray engineers used a wireless, signalpolling technique that keeps all lifts updated on what each is doing. If lifts are at different heights, for example, the system detects when that difference exceeds user-defined limits, stops the process, and alerts the operator. The system also monitors energy-level variations from battery to battery and load-distribution variations from wheel to wheel. The lifts can use any of 16 discrete channels within the frequency band for the clearest channel.

By getting rid of the cabling, Gray's Column Lifts simplify setup, eliminate any special electrical needs at the site, free the application from being tethered to an outlet, and give technicians open and safe access to the underside of a vehicle.