Protect transducers from environmental hazards

A recent poll on the SpaceAge Control Web site asked visitors, "Which environmental hazard causes your position transducers the most problems?" Topping the list of responses were vibration (21%), shock (14%), low or high pressure (12%), and dust and debris (11%).

Vibration and shock can cause sensors to fail and yield bad results. Tom Anderson, application development manager for SpaceAge Controls (Palmdale, CA; www.spaceagecontrol.com), says vibration can fatigue mechanical parts, such as sensor mounts, causing them to break prematurely. Excessive shock can sometimes dislodge components from a sensor's internal electronics. Vibration can also overload a sensor's input, causing erroneous outputs, especially in high-resolution applications.

What can you do to avoid these problems? First, says Anderson, you should specify and purchase a position transducer designed for your test environment. Of course, this is not always possible, given budget, time, and other constraints.

If specifying the ideal transducer isn't possible, here are some ways you can mitigate the environmental hazards listed in the SpaceAge Controls poll:

Cushion the sensor to change its resonant frequency and protect it from the effects of vibration. Or, use mechanical fixtures to isolate the sensor from the vibration.

As with vibration, you can protect a sensor from shock by cushioning it to isolate it and change the resonant frequency. You can also change the position of the sensor to see if the shock axis contributes to the failure.

Provide passages that will allow pressures to equalize, thus reducing the pressure on the sensor.

To prevent dust and debris from entering the sensor cavity and damaging a sensor, apply positive air pressure to the cavity to force them out. Also, cover damage-sensitive areas with appropriate plates, screws, and other covers.

While it is often said "to err is human," one way to help protect sensors from humans is to train them in the proper use and care of sensors.

If high temperature is a problem, cool or insulate the sensor area or consider moving the sensor away from the heat source.

To keep sensors dry, put the sensor in an appropriate enclosure, apply suitable adhesive-lined shrink tubing or silicone to any opening that can admit moisture, or apply positive pressure to the sensor cavity to keep out moisture.

If you must operate a sensor in a low-temperature environment, consider insulating the sensor or heating the sensor cavity.

Coat the sensor with corrosion-inhibiting coatings or enclose the sensor in an appropriate enclosure and wash it periodically.

Try changing the position of the sensor to make it less susceptible to magnetic fields. Also, use fixtures to mechanically isolate the sensor from the magnetic field.