September 1997, Issue 86

PC/104 Quarter:
Motion Control with PC/104

MONITORING THE ENVIRONMENT

If you can see it, you can control it. So, sensing devices lie at the heart of any system. They must work in the most extreme environments--vibration, dust, dirt, oil, grease, temperature, and electrical noise--and yet they're often ignored until they fail.

To ensure full sensor compatibility and system integrity, it's crucial to know the application's specifications for voltage, current sink or source operations, propagation delays, hysteresis, as well as any need of solid state or hard contact, before a sensor is selected.

Know the sensor real-time capabilities--the operational speed from the time the action is sensed until the signal reaches the controller--before selecting it. Know all the environments it will have to operate in.

Endurance requirements, environmental temperature, NEMA housing style, noise, solid state versus mechanical, and many other characteristics are critical to sensor selection. Power source requirements (e.g., voltage, current and acceptable leakage current levels, and AC or DC system operation) play a significant role.

Also, think about the properties of the item to be sensed. Is it sensitive to light or heat? Can it be touched?

These factors, along with accuracy and repeatabilty requirements, are important in choosing the appropriate sensor. But, it's the specific task to be accomplished that defines the initial sensor requirement.