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- since 1996 -

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Technical Discussions
Douglas Mendes
NDT Inspector, R & D
Imetrix Inc., USA, Joined Oct 1999, 7

Douglas Mendes

NDT Inspector, R & D
Imetrix Inc.,
USA,
Joined Oct 1999
7
04:19 Oct-20-1999
long UT cabling dB loss

I'm looking for a signal amplifier positioned at the equipment side of the cable to compensate for dB attenuation loss from 1000ft of RG-179 cable using a 5Mhz spherically focused immersion transducer.


    
 
 
Wieslaw Bicz
Wieslaw Bicz
05:00 Oct-20-1999
Re: long UT cabling dB loss
: I'm looking for a signal amplifier positioned at the equipment side of the cable to compensate for dB attenuation loss from 1000ft of RG-179 cable using a 5Mhz spherically focused immersion transducer.

Does your transducer work only as receiver or is it sending too.

Wieslaw Bicz



    
 
 
Douglas Mendes
NDT Inspector, R & D
Imetrix Inc., USA, Joined Oct 1999, 7

Douglas Mendes

NDT Inspector, R & D
Imetrix Inc.,
USA,
Joined Oct 1999
7
05:25 Oct-20-1999
Re: long UT cabling dB loss
: I'm operating my transducer in the pulse-echo mode and it will be housed inside a submerged ROV. I am not limited to this type of transducer and have started looking at others.A 2.25Mhz focused seem to work somewhat o.k.
: : I'm looking for a signal amplifier positioned at the equipment side of the cable to compensate for dB attenuation loss from 1000ft of RG-179 cable using a 5Mhz spherically focused immersion transducer.

: Does your transducer work only as receiver or is it sending too.

: Wieslaw Bicz




    
 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 519

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
519
05:43 Oct-20-1999
Re: long UT cabling dB loss
: I'm looking for a signal amplifier positioned at the equipment side of the cable to compensate for dB attenuation loss from 1000ft of RG-179 cable using a 5Mhz spherically focused immersion transducer.

You wont get much improvement from a preamplifier at the equipment side, since it can't do much that the flaw detector shouldn't be able to. It might be worth trying a High voltage High gain flaw detctor which is optimised for deep penetration applications. (I'd obviously suggest the Sonatest Powerscan 400!!)

However you should get much better results if you can mount a remote pulser/preamplifier down on the ROV - (we dont make these, so I can be objective) They arn't big, so in principle it should be possible. You'll obviously need more wires (Transmit, receive and power) but I'd reckon that the results should be a lot more sucessful. If you work with ROV's you presumably understand all the issues about cables, connectors, waterproofing etc, or at least know someone who does.

Good luck

Joe





    
 
 
Wieslaw Bicz
Wieslaw Bicz
06:46 Oct-20-1999
Re: long UT cabling dB loss

: : I'm operating my transducer in the pulse-echo mode and it will be housed inside a submerged ROV. I am not limited to this type of transducer and have started looking at others.A 2.25Mhz focused seem to work somewhat o.k.
: : : I'm looking for a signal amplifier positioned at the equipment side of the cable to compensate for dB attenuation loss from 1000ft of RG-179 cable using a 5Mhz spherically focused immersion transducer.

: : Does your transducer work only as receiver or is it sending too.

: : Wieslaw Bicz

n this case is the problem larger, because you need to transmit the pulse from
the sender.

Our PC-ultrasonic testing card is made with the separate pulser@receiver
(matchbox size), that can be used with long cable (see please the info:
http://www.optel.com.pl/manual/english/osc2.htm .

The only problem can be: we havent tested it with a 1000ft long cable and we are
using 2 cables (it is necessary to transmit more signals and to supply power for
the device - and we haven't fund a single cable suitable for this purpose).

It could be possible to use our pulser with other devices.



    
 
 
Rainer Meier
R & D
retired from intelligeNDT Systems & Services, Germany, Joined Nov 1998, 15

Rainer Meier

R & D
retired from intelligeNDT Systems & Services,
Germany,
Joined Nov 1998
15
09:01 Oct-20-1999
Re: long UT cabling dB loss
RG 179 is a standard cable with an impedance of 75 Ohm and is used in
many kind of applications. I don't have experience with RG 179, but with
RG 174 (50 Ohm), which is also a widely used standard cable. My
experience was, that it showed a quite high damping and the shielding
against electromagnetic fields was not so good, as it could. You might
get trouble using long cables in a "noisy enviroment". You have a cable
with a length of appr. 300 m and your caple is like an antenna for
electromagnetic waves. Isn't your UT-signal disturbed?
We also use UT-cables with a length of up to 300 m.Some years ago we
exchanged all of our RG 174-cables with Raychem EPD 62499 (3-fold
shielded) and we are free of trouble since this time. The shielding of
Raychem 62499 for example is more than 40 x better as RG 174 and the
signal losses are also much lower!!

But if your equipment has an input-impedance of 75 Ohm, the above
mentioned cable wouldn't suit you, because you could get trouble
due to reflection of the electrical signal on the input. But I'm
shure, that there is also an optimized 75 Ohm cable available, which
is suitable for you.


: : I'm operating my transducer in the pulse-echo mode and it will be housed inside a submerged ROV. I am not limited to this type of transducer and have started looking at others.A 2.25Mhz focused seem to work somewhat o.k.
: : : I'm looking for a signal amplifier positioned at the equipment side of the cable to compensate for dB attenuation loss from 1000ft of RG-179 cable using a 5Mhz spherically focused immersion transducer.

: : Does your transducer work only as receiver or is it sending too.

: : Wieslaw Bicz




    
 
 

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