If the penetrameter is placed on film side it is not susceptible to the same unsharpness variables that are present with the specimen itself (see geometric unsharpness in your code/standard). Some codes will allow this placement in certain cases if the penetrameter is marked correctly (with an F).
Manish, look at AWS D1.1 or ASME Sect V. They both have penetrameter charts based on the material thickness. When the penetrameter is placed Film-Side, a smaller one is mandated. Thus the requirement for the lead letter 'F' to be placed on the penetrameter. As TJ noted, a Film-Side penetrameter will be much clearer in the RT image, so a smaller one is required to prove the sensitivity of the image.
I have seen the posts in response to your request they have all provided the correct information but I think they have not answered your question.
1. Penetrameter what is the other name for this item? It is IQI or image quality indicator.
What is a radiographic image? It is an image of a part that has been exposed to radiation showing density variations. Therefore a penetrameter confirms the minimum resolvable density variation.
From this you should be able to determine why the IQI is on the source side or as Roger Duwe has said a smaller penetrameter is placed on the film side to prove sensitivity.
As per the code requirement the Penetrameter shall be kept at source side whenever practicable.
This is required for -
1. To check the Ug unsharpness is not exceeding the acceptable limit. If Ug exceeds then you will not able to see the required wire or hole for that Thickness.
2. It ensures that it will show the minimum discontinuity throughout the job thickness equivalent to wire dia. or hole dia. when you can see the particular wire or hole when the Penetrameter is kept on Source side.
3. Whenever you are keeping the Penetrameter on film side code asks to view smaller diameter wire /hole to compensate the absorption through the job thickness.
1. Just because Ug exceeds acceptable limits, this does not mean that you will not see the penetrameter holes.
2. I would not refer to the penetrameter holes as guidlines for minimum discontinuity or in any other way related to acceptance criteria. It is to determine sensitivity of the radiograph. This can confuse new technicians.
3. Compensating for absorption has nothing to do with film/source side placement. It is simply the geometric effects related to forming the image.