Test circuit

Typical measurement setup for SECO ultrasonic transducers | Electroacoustic parameters

To measure our ultrasonic transducers, we use a proven test circuit internally at SECO. This forms the basis for the technical data in our product data sheets. This circuit can be reproduced for the initial installation of our products. Of course, our ultrasonic transducers can also be operated with a wide variety of customer-specific test circuits. For tips and tricks, please contact our ultrasonic experts! We look forward to hearing from you.

Measurement setup & test circuit

Pulse-echo mode

Electronic accessories

Driving electronics / DAC:

Excitation of the ultrasonic transducer
Generation of pulse or sinus burst signal and frequency control

Antiparallel diodes z.B. BAV20:

Smoothing of the signal, protection of sensitive electronic components from voltage peaks

Reflector at defined distance:

only in pulse-echo mode
at least 100 x 100 mm, flat surface
longitudinal axis vertical to the transducer

amplifier:

if oscilloscope / ADC has no integrated amplification unit
especially for high-frequency transducers with low echo voltages
Increased signal-to-noise ratio, bandpass to suppress interfering frequencies

Oszilloscope /ADC:

Digitization and evaluation of the received signal
Signal visualization with regard to signal shape
Amplitude and frequency in real time, frequency analysis

BNC connection cable (recommended):

Better signal quality, minimized signal distortion, especially at high frequencies
Maximum freedom from interference, connection stability

Transducer-specific settings of the test circuit

We basically distinguish between three types of transducer, which we have optimized for their different strengths in terms of their electro-acoustic functionality and design.

Product group	SC007	SC010	SC021	SC029	SC031	SC042	SC049	SC508	SC517	SC520	SC524
Excitation voltage at the transducer [Vpp]	10	10	10	10	10	10	10	10	10	10	10
Excitation type	Sinus	Sinus	Sinus	Sinus	Sinus	Sinus	Sinus	Sinus	Sinus	Sinus	Sinus
Burst cycles	40	40	12	12	12	12	12	40	12	12	12
distance transducer-reflector [mm]	460	288	100	60	60	60	60	432	100	100	100
Data sheet	DB007	DB010	DB021	DB029	DB031	DB042	DB049	DB508	DB517	DB520	DB524

Size of the reflector at least 100 x 100 mm, longitudinal axis of the transducer vertical to the reflector

Product group	SC008	SC012	SC020	SC030	SC040	SC041	SC050
Excitation voltage at the transducer [Vpp]	10	10	10	10	10	10	10
Excitation type	Sinus	Sinus	Sinus	Sinus	Sinus	Sinus	Sinus
Number of burst cycles (Sinus)	80	80	80	80	80	80	80
distance transducer-reflector [mm]	647	432	259	120	130	130	120
Data sheet	DB008	DB012	DB020	DB030	DB040	DB041	DB050

Size of the reflector at least 100 x 100 mm, longitudinal axis of the transducer vertical to the reflector

Product group	SC108	SC112	SC116	SC125.2	SC125.21	SC135	SC150
Excitation voltage at the transducer [Vpp]	200	200	200	200	200	200	30
Excitation type	Pulse	Pulse	Pulse	Pulse	Pulse	Pulse	Sinus
distance transducer-reflector [mm]	130	100	100	60	60	60	60
Data sheet	DB108	DB112	DB116	DB125.2	DB125.21	DB135	DB150

Size of the reflector at least 100 x 100 mm, longitudinal axis of the transducer vertical to the reflector

Electroacoustic parameters

Measured with our SECO-specific test circuit, the following electro-acoustic parameters result for our product groups:

Product group	SC007	SC010	SC021	SC029	SC031	SC042	SC049	SC508	SC517	SC520	SC524
Echo voltage (unamplified) [mVpp]	> 5	> 4	> 10	> 3,3	> 8,2	> 6,4	> 0,6	> 6	> 12	> 11,2	> 10
typ. echo voltage (unamplified) [mVpp]	6…11	5…11	~ 13	~ 4,5	~ 11	~ 8,5	~ 0,8	7…12	~ 16	~ 15	~ 13
ringdown voltage [mVpp]	10	10	10	10	10	10	10	10	10	10	10
ringdown time @ ringdown voltage [µs]	< 1500	< 1000	< 350	< 150	< 175	< 140	< 80	< 1600	< 330	< 290	< 270
Data sheet	DB007	DB010	DB021	DB029	DB031	DB042	DB049	DB508	DB517	DB520	DB524

Product group	SC008	SC012	SC020	SC030	SC040	SC041	SC050
Echo voltage (unamplified) [mVpp]	> 30	> 25	> 17	> 12	> 4	> 4	> 2,8
typ. echo voltage (unamplified) [mVpp]	40…75	35…50	20…35	~ 15	5…9	5…9	3,5…4
ringdown voltage [mVpp]	10	10	10	10	10	10	10
ringdown time @ ringdown voltage [µs]	< 2800	< 1800	< 1000	< 570	< 420	< 420	< 300
Data sheet	DB008	DB012	DB020	DB030	DB040	DB041	DB050

Product group	SC108	SC112	SC116	SC125.2	SC125.21	SC135	SC150
Echo voltage (unamplified) [mVpp]	> 6,0	> 6,5	> 6,0	> 2,5	> 1,5	> 1,2	> 0,3
ringdown voltage [mVpp]	1,0	0,25	0,15	0,1	0,08	0,06	0,15
ringdown time @ ringdown voltage [µs]	< 700	< 450	< 390	< 320	< 320	< 192	< 55
Data sheet	DB108	DB112	DB116	DB125.2	DB125.21	DB135	DB150

General conditions for measuring the electroacoustic parameters:

Excitation type, burst cycles and distance between transducer and reflector see “Transducer-specific settings of the test circuit”
Size of the reflector at least 100 x 100 mm, longitudinal axis of the transducer vertical to the reflector
Medium air at room temperature and a relative humidity < 25 %

Signal diagram

Typical echo signal of an ultrasonic transducer after sinus excitation:

Schematischer Signalverlauf Ultraschallwandler

Details of the signal curve:

UA = ringdown voltage
UE = echo voltage
bc = number of burst cycles
rc = number of echo-ringdown cycles (UE to 1/2 UE)

Typical directivity plot

Directional characteristics and opening angle of the three transducer types

Focused transducer

Directional transducers are characterized (according to their name) by a very narrow sound beam and a small opening angle.

Typical values here are approx. 7…11° (@ -3dB). Comparatively large ranges are possible with them, which is why they are often used in distance measurement, level measurement, presence detection, etc.

Multi-use transducer

In contrast, our single transducers have a particularly wide sound beam and large opening angles of typically approx. 12…20° (@ -3dB).

These transducers are primarily used in areas where the sound beam is blown away (wind measurement in an anemometer, flow measurement).

A wide sound beam enables precise measurements even at very high flow velocities.

Pulsed transducer

The opening angle of our pulse transducers depends on the frequency due to the broadband characteristics of this transducer.

The directional diagram therefore shows two additional frequencies below and above the typical operating frequency.

Alternative operating principle: Transmitter-receiver mode

Customers typically use our ultrasonic transducers in transmitter/receiver mode for measurement tasks such as flow measurement, double sheet control, web edge control, label detection and presence control. The ultrasonic signal travels between two transducers (transmitter and receiver) and is then evaluated. The travel distance is therefore only half as long as in pulse-echo mode, where a single transducer emits sound against a reflector.

Ansteuerung Sender Empfänger Prüfschaltung

Background information on the test circuit

Ultrasonic transducers generate and receive sound waves in the ultrasonic range. Their functionality and performance are tested using a test circuit. This comprises several key components. First, a function generator or high-voltage generator is used to generate an electrical signal that drives the ultrasonic transducer. This signal is then passed through a power amplifier to ensure it is strong enough to activate the transducer.

The transducer itself converts the electrical signal into mechanical vibrations that are emitted as ultrasonic waves. These waves can then be detected by a receiver, often a second transducer. The receiver transducers the ultrasonic waves back into an electrical signal.

This signal is then amplified by a preamplifier and sent to an oscilloscope or spectrum analyzer. With these instruments, the user can analyze the frequency, amplitude and shape of the received signal. By comparing the output and input signals, the performance and accuracy of the ultrasonic transducer can be evaluated. These test circuits are essential to ensure that ultrasonic transducers perform accurately and reliably in medical, industrial and scientific applications