How to choice cobalt EM strips?
There are some questions should be clearly know first:
1. What kind of strip feature is used for the burglarproof system?
This strip is made from non-crystal material which is composed by some high temperature molten metal that was spouted out from the quartz nozzle in a very short time with a high speed to form solid strip. Present cobalt and iron strips are made from non-crystal material. This kind of non-crystal has a high permeability with rational components and scientific process. So its high permeability is used for alarming.
2. Since iron strip and cobalt strip are both made from non-crystal material, should both of them have high permeability for burglarproof strips for books?
Theoretically, the answer is YES. But the magnetization of cobalt strips is different from iron strips actually because of many factors. Their permeability stress is different from each other. Iron strips will be influenced more than cobalt strips. Some users might find that the new strips worked normally, but after being set inside the books and the gumwater was dry, they could not alarm in the detecting channels or there was a large blind area. That was because of the stress. When the gumwater is dry, the paper will have a shrinking stress which will cut the permeability down, so the detectors could find weak signal only or no signal at all, that reduces the sensibility. Some iron strips will lose their sensibility at all. But this kind of stress has less influence on cobalt strips.
3. Could cobalt strips make it safe perfectly?
Not always. But cobalt ones are much better than iron ones. Cobalt strips will never lose their sensibility. (Generally, the sensitivity of normal stress cobalt strips becomes 40%~70% of its original sensitivity after being set inside the books and the sensitivity of negative cobalt strips won¡¯t change.) But why the systems in some libraries still have low sensitivity with cobalt strips? The high quality cobalt strip has certain proportion of cobalt (60%~70%) with rational producing processes. There are many manufactories producing EM strips presently with different material proportion and cobalt proportion. The producing processes are relative to the operators¡¯ working experience closely. So cobalt strips are not always the high qualified EM strips.