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- since 1996 -

Matec Instrument Companies, Inc.
Ultrasonic test instrumentation and systems for scientific research, quality control inspection and production testing applications.
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Technical Discussions
Kris Van de Rostyne
Kris Van de Rostyne
06:30 Mar-28-2003
line driver

Hello,
Some piezoelectric ultrasonic sensors seem to include a so-called 'line-drive transformer'. Can anybody inform me about the function or usefulness of this component, or where I could find more information?
Thanks in advance,
Kris



 
 Reply 
 
Paul Meyer
R & D,
GE Inspection Technologies, USA, Joined Nov 1998, 47

Paul Meyer

R & D,
GE Inspection Technologies,
USA,
Joined Nov 1998
47
03:09 Mar-28-2003
Re: line driver
Hi Kris,
A piezoelectric transducer generates an electric charge when it receives an acoustic signal. If the transducer is connected to a long coax cable, the charge is distributed over the cable capacitance, reducing the signal amplitude. The "line driver" that I know is an amplifier with a high ipedance input that is able to generate a much larger signal so that the amplitude is sufficient at the far end of the cable. These are normally used when the cable between the transducer and the instrument is very long (10s of meters)
Also, a transformer may be used to match the impedance of the transducer to that of the cable or instrument but I believe you refer to the device described above.
Paul

: Hello,
: Some piezoelectric ultrasonic sensors seem to include a so-called 'line-drive transformer'. Can anybody inform me about the function or usefulness of this component, or where I could find more information?
: Thanks in advance,
: Kris
.



 
 Reply 
 
Uli Mletzko
R & D, Retired
Germany, Joined Nov 1998, 89

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
05:56 Mar-30-2003
Re: line driver
: Hello,
: Some piezoelectric ultrasonic sensors seem to include a so-called 'line-drive transformer'. Can anybody inform me about the function or usefulness of this component, or where I could find more information?
: Thanks in advance,
: Kris

Hallo Kris,

a transformer, which is integrated into the housing of a piezoelectric sensor, is acting as a matching network.
It is matching the 'wave resistance' Z of the coaxial cable (e.g. Z = 50 Ohm for cable RG 58) to the complex input impedance (impuls) respective output impedance (echo).
Unfortunately, these two impedances (for input resp. output) might be different, so one has to make a compromise for the matching network.

For details, google for 'high frequency transmission lines', 'impedance matching', 'wave restistance', 'standing wave ratio'. Most of this is related to radio or tv engineering or to rf measuring techniques.

Regards Uli Mletzko
MPA NDT Group,
University of Stuttgart,
Germany


 
 Reply 
 
Joerg Schulze-Clewing
Joerg Schulze-Clewing
04:53 Apr-03-2003
Re: line driver
Hi Kris,

A transformer is one option but when it comes to
maintaining the best possible signal-to-noise ratio it
is better to place some of the electronics near the
transducer. In a pulsed application this would be a
pre-amplifier, a T/R switch and maybe even the pulser.

Reason for this is that while a transformer can match
impedances it cannot prevent losses due to the non-
resistive nature of the transducer, at least not in
a short-pulse (wideband) application.

Greetings (groetjes),

Joerg.

: Hello,
: Some piezoelectric ultrasonic sensors seem to include a so-called 'line-drive transformer'. Can anybody inform me about the function or usefulness of this component, or where I could find more information?
: Thanks in advance,
: Kris
.



 
 Reply 
 
jayaraman
jayaraman
09:13 Oct-08-2003
Re: impedance transformation in hf radio frequency lines
: : Hello,
Will somebody enlighten me on exponential transformation of impedance in rf feeder lines especially in the context of short wave line transmission?
jayaraman
: Hallo Kris,
.
: a transformer, which is integrated into the housing of a piezoelectric sensor, is acting as a matching network.
: It is matching the 'wave resistance' Z of the coaxial cable (e.g. Z = 50 Ohm for cable RG 58) to the complex input impedance (impuls) respective output impedance (echo).
: Unfortunately, these two impedances (for input resp. output) might be different, so one has to make a compromise for the matching network.
.
: For details, google for 'high frequency transmission lines', 'impedance matching', 'wave restistance', 'standing wave ratio'. Most of this is related to radio or tv engineering or to rf measuring techniques.
.
: Regards Uli Mletzko
: MPA NDT Group,
: University of Stuttgart,
: Germany
.



 
 Reply 
 

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