One of the great features, and subsequent benefits, of ultrasonic technology is that because the principle of operation is based on the time of flight of a sound pulse, nearly all ultrasonic sensors have the inherent ability to measure distance rather than give just a switched output. Only the connection circuitry determines the sensor’s output signal as analogue or a digital switch, meaning the cost of the measurement version is often not significantly higher than the switch point. This has led to the widespread adoption of analogue ultrasonic sensors in complex applications. The ability to offer measurement gives operators the flexibility to adjust their decision points (switch points) on the fly, or to use a range of measurements programmed in the PLC. But for simpler applications (particularly where the budget is limited) the cost of including an analogue input interface card in the controlling PLC can often be prohibitive and lead designers to revert back to the less flexible switch point control to save costs.
The new F77 miniature ultrasonic sensor range from Pepperl+Fuchs is designed to offer users a very low entry level price into ultrasonic technology. When looking at application areas the developers recognised that the use of a sensor for measurement applications might be restricted, not by the cost of the sensor itself, but by the cost of the interface card. To help overcome this, variants of the F77 has been designed with a frequency output instead. This frequency output allows machine builders to use their conventional PLC digital inputs because the sensor outputs a digital frequency proportional to the measured distance. A simple pluse/sec calculation in the PLC can then be used to derive the distance to the target. The F77 frequency output sensor is available in two sensing ranges 250mm and 400mm, for more information on the full range of products search "F77".