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- since 1996 -

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Technical Discussions
Craig
,
United Kingdom, Joined Oct 2018, 3

Craig

,
United Kingdom,
Joined Oct 2018
3
20:44 Oct-29-2018
RT - Changing film density

Good day,

I was wondering if there is a formula available to change graph density. I've seen charts made with "multipliers" but I haven't been able to find the formula behind this...

e.g. Film density of 1.00 , increase this to 2.00 - multiply exposure by 2.5
e.g. Film density of 1.00 , increase this to 3.00 - multiply exposure by 4.0

Are these 'multiplier' charts made from characteristic curve from film manufacturers?

Many thanks.

Srinivas
NDT Inspector,
kalva engineers pvt ltd, India, Joined Oct 2012, 35

Srinivas

NDT Inspector,
kalva engineers pvt ltd,
India,
Joined Oct 2012
35
08:57 Oct-30-2018
Re: RT - Changing film density
In Reply to Craig at 20:44 Oct-29-2018 (Opening).

Use characteristic curves pkz

Dr. Uwe Zscherpel
Director,
BAM Berlin, Germany, Joined Jan 2010, 89

Dr. Uwe Zscherpel

Director,
BAM Berlin,
Germany,
Joined Jan 2010
89
10:57 Nov-05-2018
Re: RT - Changing film density
In Reply to Srinivas at 08:57 Oct-30-2018 .

The characteristic curves for NDT films are just linear (+/- 10%), i.e. double of exposure will double the optical film density. But there is an offset of about 0.2 which is caused by fog and base density, which has to be subtrated first and added after density correction!

Angel
,
Poland, Joined May 2018, 5

Angel

,
Poland,
Joined May 2018
5
19:31 Nov-12-2018
Re: RT - Changing film density
In Reply to Dr. Uwe Zscherpel at 10:57 Nov-05-2018 .

In my opinion this formula is useless because of attenuation of developer. Old or weaker developer loses linear property

Dr .Uwe Zscherpel
Director,
BAM Berlin, Germany, Joined Jan 2010, 89

Dr .Uwe Zscherpel

Director,
BAM Berlin,
Germany,
Joined Jan 2010
89
21:20 Nov-12-2018
Re: RT - Changing film density
In Reply to Angel at 19:31 Nov-12-2018 .

Dear Angel,
of cause, if you use a non-propriate developer system you should expect problems and non-linearities. Therfore, ISO 11699-2 defines a method to check the status of your developing system using pro-exposed film test strps fro mthe film manufacturer. If the result of this test is acceptable, the NDT film is linear at least for optical densities up to 4.5 above fog and base.
At BAM we are doing film system certification of the major film manufacturers since decades and have therefore some experience...
Uwe Z.

Angel
,
Poland, Joined May 2018, 5

Angel

,
Poland,
Joined May 2018
5
22:29 Nov-12-2018
Re: RT - Changing film density
In Reply to Dr .Uwe Zscherpel at 21:20 Nov-12-2018 .

Dear Dr. Uwe Zscherpel
Of course, you right!!! Only way is keep proper developer system in manual develop
What system do you use, manual or auto?
If you use auto develop you don't need make test exposure? In my opinion old developer in pipe system is problem and disrupts linearity. If you work each day it's no problem. Worse when radiographic testing is make one day a week.
In sum:
In manual develop it works
In auto can appear a problem depend of frequency of RT

Dr. Uwe Zscherpel
Director,
BAM Berlin, Germany, Joined Jan 2010, 89

Dr. Uwe Zscherpel

Director,
BAM Berlin,
Germany,
Joined Jan 2010
89
14:18 Nov-19-2018
Re: RT - Changing film density
In Reply to Angel at 22:29 Nov-12-2018 .

Dear Angel.
which automatic film processor are you using? We use since decades AGFA processors and NO longer any manual developement. The processors have a mode which move the rolls once within a hour when not used and also pump some liquids through the pipes to avouid any degradation of the development. If you regularily check your machine using ISO 11699-2 PMC strips (morning and evening when developing), then the developing machine is in good condition for at least 3 months weekly work. Than the fresh developer in the storage tank becomes really brown and the ISO strips show deviations more than 10% from the certified reference values. It becomes time to exchange the complete chemistry and to clean the maschine. We as accredited testing lab have this as a quarterly service and are living very well with it.
Uwe Z.

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