Measurements are all about change, detecting change in an application and providing the new information to an operator or control system. However, analyzing the requirements of a specific application and applying the latest technology can change the accepted approach for the measurement. This can occur to satisfy end product trends for cost reduction, higher performance, smaller form factor, increased ruggedness and/or increased functionality. These trends in turn become the trends for the sensors.
One example of the combination of new technology and a changing environment involves pick-and-place equipment for semiconductor manufacturing. A pressure sensor is the measurement of choice and could use a Microelectromechanical system (MEMS) or other sensing technologies to determine proper operation of the equipment. Smaller semiconductor packages require smaller nozzle diameters and shorter tact times in pick-and-place applications, says Donna Sandfox, product manager, MEMs Sensors, Omron Electronic Components LLC. As a result, detecting the flow through the nozzle can provide a higher sensitivity and faster response than sensing pressure.
Sensing an opportunity, Omron engineers utilized MEMS technology to create a thermopile element that converts thermal energy into electrical energy. The D6F-03 unidirectional MEMS mass flow sensor measures mass airflow up to 3l/min with a ±5 percent full-scale repeatable accuracy. To be as close as possible to the measurement point, a small 16.8- Χ 8- Χ 36.6-mm package was developed.
Changing the Playing Field
Another alternate sensing approach involves detecting excessive vibration in rotating equipment to shutdown the equipment at a critical point and minimize damage or prevent failure. An obvious and frequently used methodology involves an accelerometer, a power switch such as a triac and additional electronics. Pursuing a lower cost solution, the IMI Sensors Div. of PCB Piezotronics chose magnetic technology for a simple integrated switch. The design uses a spring-loaded, magnetically coupled sensor with external mechanical adjustments for higher or lower sensitivity. The Model 685A07 mechanical vibration switch requires no power to operate and targets cooling towers, fans, small motors or pumps or any installation that requires immediate shutdown when increased vibration levels occur.
Sensor trends covered in more detail in this section include those in photoelectric sensors, vision sensors and motion feedback devices (encoders).