Imagine a paper X builds a new sensor, and then uses the new sensor to detect protein Z. When citing paper X, I might want to point out that they've build a new sensor. EG:
"New sensors have been recently proposed that explore effect A[cite paper X]."
Then later, I want to talk about protein Z. I should probably cite paper X again, since they did important work on protein Z...
"Protein Z has been studied using similar techniques [cite paper X, cite paperY]"
Essentially, paperX did two distinct things that are pertinent to my article. I'd like to refer to both of them, so is it ok to cite paper X twice? While it will only appear in the bibliography once, there will be two references to it in the inwork citation. Is this generally acceptable?