Reference: see explanation

Reference information:
it sounds as if Rezeptbetrieb is something similar to a semi-automatic process.

To me this Rezept sounds like a process description of some kind - probably a "how-to-mix-this-makeup" sort of recipe.
And at some point in this recipe, the automator needs to do something (add an ingredient, ...) manually and is therefore called to the machine.
This call is also part of the recipe. The rest before and after this call is done automatically according to the process steps.

(In cooking it would read something like "...then let it steam for a while. As soon as your see this and that happen, you need to add more butter" or whatever.)

Is that understandable?

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Note added at 43 Min. (2009-10-27 12:08:30 GMT)
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Die Sirene ertönt nur im Rezeptbetrieb sobald vom Rezept der Bediener zur Anlage für einen manuellen Eingriff gerufen wird.

Okay, I just pointed this out in a comment to jtgoaler's answer. If you are very picky about the German, there are two ways to interpret the "nur":
1. the sirene only sounds when the Rezeptbetrieb is used and the operator needs to do something
2. the sirene sounds in any operation mode when the operator needs to do something.
Doesn't sound like much of a difference?
Well, as I said, you need to be picky.