where expertise comes together - since 1996 -

The Largest Open Access Portal of Nondestructive Testing (NDT)

Conference Proceedings, Articles, News, Exhibition, Forum, Network and more

where expertise comes together
- since 1996 -

870 views
Technical Discussions
elgazery
Consultant
National Institute for Standards, Egypt, Joined May 2003, 10

elgazery

Consultant
National Institute for Standards,
Egypt,
Joined May 2003
10
01:28 May-11-2001
Difference between dB and dBM

Please
there are any one can discuss me the difference between dB and dBM units for measurement attenuation.
Thank you in advance.
looking forward to recieve your valuable discussion.
elgazery@sit.nis.sci.eg


    
 
 
jean paul van Cuyck
Director
A2MS, Applied Acoustics, Materials and Systems, France, Joined Nov 1998, 13

jean paul van Cuyck

Director
A2MS, Applied Acoustics, Materials and Systems,
France,
Joined Nov 1998
13
04:16 May-11-2001
Re: Difference between dB and dBM
: Please
: there are any one can discuss me the difference between dB and dBM units for measurement attenuation.
: Thank you in advance.
: looking forward to recieve your valuable discussion.
: elgazery@sit.nis.sci.eg
.
dB or dBW relativ to 1W
dBm for dB relativ to 1 milliwatt. 0 dBm= 1 mW = -30dBW



    
 
 
Dr. Sotirios J. Vahaviolos
R & D, -
MISTRAS Group, Inc., USA, Joined Jan 2000, 15

Dr. Sotirios J. Vahaviolos

R & D, -
MISTRAS Group, Inc.,
USA,
Joined Jan 2000
15
05:43 May-11-2001
Re: Difference between dB and dBM
: : Please
: : there are any one can discuss me the difference between dB and dBM units for measurement attenuation.
: : Thank you in advance.
: : looking forward to recieve your valuable discussion.
: : elgazery@sit.nis.sci.eg
: .
: dB or dBW relativ to 1W
: dBm for dB relativ to 1 milliwatt. 0 dBm= 1 mW = -30dBW
.
Dear Mr.Elgazery
Its interesting,but these terms are used interchangeably at times, erroneously.The term dBm is used by
communications engineers and it is absolute.Most Power meters commercially available have this scale.
It is : dBm=10log(base 10)(P1/P2) at two different Power points.Power is read always across a 50 Ohm
resistor.IEEE has made this a standard and 1mW=0dBm(-40dBm is 100nW accross 50 Ohm and +20dBm is 100mW).
As far as I know dB(not DB)refers simly to gain(and loss/attenuation as -dB).It is different this time
as the equation is not Power but a simple ratio: dB=20log(base 10)(Gain or attenuation).One can have
a reference and above that reference he is talking in positive dBs(Gain) and below in negative dBs(loss
or attenuation).Such scales can then be modified as we have done for Acoustic Emission where we talk in
dBae and our refence is the "perfect" sensor giving us ONLY 1microVolt(!) Peak output noise.Anyway a
good goal.So for 40dBae a sensor/Amplifier(40dB Gain)output across a 50 Ohm resistor is 10mV.
Sotirios



    
 
 

Product Spotlight

EKOSCAN Phased Array

In order to always fit your needs, EKOSCAN can manufacture any type of UT transducer, either convent
...
ional or Phased Array. As an ISO 9001: 2015 certified company, EKOSCAN is extremely careful as far a material selection and manufacturing processes are concerned. Our probes guarantee our customers the benefits of latest innovations regarding piezo-composite, backing, impedance adaptation layer, etc. Specific probes for hostile environment: high temperature, high pressure, corrosive environment,etc. Specific probes designed to fit your specific application: optimization of every parameter to guarantee you the best detection.
>

Alpha Pro Digital Radiography System

The Alpha Pro digital X-ray system is the ideal system for your NDT \r\nneeds, as it offers amazin
...
g 16 bit images which enable the highest \r\nlevel of detection and identification of hairline cracks. While weighing only 3kg (6.6lbs), this panel has the largest imaging area: 35 X 43 cm (14X17 in).
>

iProbe - USB Phased Array Probe

Turn your PC, Laptop or Tablet into a powerful 32:64 Phased Array system with our USB powered Phas
...
ed Array iProbe and inspection software package. Perform affordable weld inspection and corrosion mapping inspections with this powerful but small system. The probe has a 100V pulser, 8K PRF, dual axis encoder input and achieves outstanding signal quality.
>

Conformable wedge transducer

The conformability is obtained with a flexible membrane filled with water between the transducer and
...
the inspected component. The coupling between the membrane and the component requires a small quantity of water or couplant. The conformable wedge combines the acoustic performance of immersion technique with good coupling and low attenuation.
>

Share...
We use technical and analytics cookies to ensure that we will give you the best experience of our website - More Info
Accept
top
this is debug window