EGE-Elektronik Spezial-Sensoren GmbH - Special-Sensors for Automation

Ultrasonic sensors - Technology and application

Basics
Ultrasonic sensors are transmitting and receiving ultrasonic signals. These signals have a frequency range from 65 kHz up to 300 kHz. Ultrasonic sensors can be used for several different applications, for example:

diameter detection
looptension
height detection
level measuring
counting

Application notes

Non-contact detection of:

distances
presence
level
diameter
position

Independent of:

material
coloure
light
smoke
dust

Cycle period

A pulse is transmitted at the time 0, reflected by an objekt, received by the transducer and again reflected. The next pulse can be transmitted when all energy of the first pulse is absorbed. This time period is called TCycle (cycle period). (Fig. 1)

cycle period
Sensors with
long sensing ranges have long cycle periods
and slow reaction time
short sensing ranges have short cycle periods
and fast reaction times

Angle of beam

The energy of the ultrasonic pulse is transmitted in form of a cone along the sensor axis. The highest intensity is on the axis and decreases with rising angles. The angle of beam is defined by the angle through which the energy of the ultrasonic pulse is reduced of 33% of its maximum value.

The best detection is given by an object that stands vertical to the transducer axis. To give a save detection, the object should not have an greater angle than half of the angle of beam (alpha /2). (Fig. 2) If the object is canted at a greater angle, there is no reflection of the ultrasonic pulses. An object with a flat surface and canted at an angle of 45° to the transducer axis refracts the ultrasonic pulse in an angle of 90°.

Angle of beam    

Voltage amplitude

During the transmission the voltage amplitude of the ultrasonic pulse is approximate 80V PP.
The pulse period of the ultrasonic pulse depends on the period of the transmission pulse and on the ringing time of the transducer.
The voltage amplitude of the received echo is in the range of V.  (Fig. 3)

Voltage amplitude

Blind zone

It is not possible to receive an echo during the transmission of the ultrasonic pulse (0 up to tpulse). This time period defines the range of the Blindzone (0 up to XD). In this Blindzone it is not possible to measure a distance. (Fig. 4)

Blind zone

Approval for safety applications
Sensors for personal security must have a qualifification approval according to EN 954-1 and must be labeled accordingly. Sensors that are not labeled must not be used for applications of this kind.

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