Honeywell Switches and Sensors manual Ultrasonic Distance Sensors

ULTRASONIC DISTANCE SENSORS

Ultrasonic Distance Sensors

Ultrasonic sensing systems offer no-touch distance measurements to an accuracy of 1 mm through dust, smoke and vapour, in areas of high noise level, and with all types of target materials, shapes and colours, with sensing ranges from 100 mm up to 6000 mm.

High performance no-touch position sensing

Increased reliability, no contamination. Honeywell ultrasonic sensors operate by exciting an acoustic transducer with voltage pulses, causing the transducer to vibrate ultrasonically. These oscillations are directed at a target and by measuring the time for the echo to return to the transducer, the distance may be calculated. This measurement technique in no way interferes with the object - it does not contaminate the target, nor does it affect the position. And being no-touch, there are no mechanical linkages to wear out.

Ultrasonic

Factory noise does not affect operation because the operating frequency is well above the frequency of ambient sound. And because sound is used, air pressure, humidity and airborne contamination have little effect on accuracy; target shape, material and colour are also not critical.

Working method

The sensors work with an ultrasonic transducer used for both transmitting and receiving. In each cycle, ultrasonic pulses will be transmitted. The pulses are then reflected back from the target, and received by the sensor. By means of the temperature compensated measurement of the elapsed time of the acoustic signal, the target distance is determined, with a high degree of accuracy. The resulting measurement can be output either as an analogue or a digital signal.

Target object distance
		Time
0	T/2	T
		Time
Voltage

Figure 1 shows the elapsed time of the acoustic pulse. The diagram shows how the pulse travels from the transducer to the target, is reflected at time T/2, and reaches the transducer at time T. Below is a diagram of the voltage at the ultrasonic transducer. Elapsed time T is directly proportional to object distance a. a = cT/2, where c is the velocity of sound.

Application criteria

The maximum sensing range depends on a number of factors such as target shape, surface, inclination to the beam axis, surface composition and environmental influences. The range values included in this catalogue are based on a target made of flat, sound-reflecting material at 25°C and still air, placed vertical to the beam axis.

Reflective properties

Almost all materials and targets reflect sound, and can therefore be detected. Only sound-absorbing materials such as cotton wool, or foam rubber are either difficult or impossible to detect. Certain materials, such as textiles, weaken the ultrasonic signals, as a result of which the maximum sensing distance is less than half of the nominal value.

Target shape and surface

All object shapes and surfaces can be measured using ultrasonic sensors, up to the maximum distance at which a sufficient echo reaches the sensor. Cylindrical, conical and small objects reduce the measuring range.

Inclination to beam angle

If a smooth, flat target is inclined at more than half of the nominal beam angle to the normal beam axis (e.g. 5°), the echo is deflected so far that, under certain conditions, no signal is received by the sensor (see Figure 2 overleaf). At shorter target distances, the target can be inclined up to the beam (e.g. 10°) from the beam axis. In the case of targets with a rough surface, the acoustic beam is reflected diffusely. The angle of inclination to the beam may, under certain circumstances, be up to 50°, but the maximum sensing distance is reduced.

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