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Spring Loaded LVDT position sensors – also known as gauging probes – are serving as integral components in control systems that ensure the accurate landing of lift cars at building floors.

As passengers travel in lifts at speeds upwards of 2,000ft/min, electromechanical control systems rely on sensors to provide the necessary feedback for proper alignment of lift cars at building floors upon arrival.

To ensure a smooth and comfortable ride, the cars are suspended by springs within an outer frame that provide cushioning against the effects of acceleration/deceleration and the initial starting and stopping jerks caused by inertia.

To ensure that cars and building floors properly align upon arrival, Macro Sensors’ Spring Loaded LVDT position sensors are used to measure the difference between the frame and car position.

Specifically, the sensors are measuring ‘spring deflection’ as a result of the passenger load.

Depending upon the elevator manufacturer, sensors are mounted either under or above the elevator car.

When measurement is made from above, the probe of the spring-loaded LVDT position is normally compressed and extends as the load increases.

When sensors are installed below the elevator platform, the probe is normally extended and compresses as load increases.

Output is fed into a control system that uses the displacement information to adjust the travel of the frame, so that, when the elevator car doors open, the car floor is level with the building floor on which passengers are exiting.

With available stroke ranges of +/-0.05 to +/-2in (+/-1.25 to +/-50mm) in both AC and DC input/output configurations, Macro Sensors’ hermetically sealed sensors (IEC IP-68) are rugged and robust, enabling them to survive heavy shocks as well as the effects of dirt, water, steam and other corrosive elements without affecting performance.

Internal construction consists of a spring-loaded shaft running in a precision sleeve bearing connected to the core of an LVDT.

The probe shaft of the position sensors is fully extended by a spring exerting a nominal force of 6 to 20oz, depending on total range.

The contact tip supplied is an AGD standard number 9 made from black-oxide-hardened tool steel.

It is fully interchangeable with other 4-48 threaded AGD contact tips.

While Macro Sensors offers its Spring Loaded LVDT Position Sensors in AC- or DC-operated versions, DC-operated units incorporate integrated electronics that provide a 4-20mA, single-ended or bipolar DC output compatible with most standard PLCs, digital indicators and data-acquisition systems.

Macro Sensors also offers metric calibration options for all Spring-Loaded LVDT Position Sensors.

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