I may need some more information regarding this operational machine, of its kind or character, and of how this slide may work within the machine structure.

I looked into some major search engine to find no results where 作動閉 is shown in an actual use. Hence, this answer is based only on my guess, please be notified of that.

I think 作動 could have a literal meaning of 'operation' or 'function', i.e. how the machine or its parts could work for a particular purpose, 閉 is the difficult term here, but I interpreted it as the 'point of close' for the operation of the machine or the slide in this case. As obvious in the first line you put in your question, this limit switch works to determine the upper and lower limits of the slide, where they need two such switches for each of the points of limitation. And the below sentence describes the case where one of the swicthes ceases to operate, which tells us that the importance of the dual exisitence of the switches for the slides for normalization.

e.g. This limit switch is to be regarded as the a point of the close of operation.

Again, this is just my guess, but I may regard it positive if it's a literal translation, at least.

It's been a few years, so I've forgotten what "作動閉a" is supposed to be and what the English equivalent is, but the context does a fairly good job of explaining what is required: a series connection.

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Note added at 2002-09-09 09:28:18 (GMT)
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For what it¥'s worth, my copy of MSIE was set to Shift-JIS when I wrote the above. It¥'s back at 自動 now.

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Note added at 2002-09-10 05:12:21 (GMT) Post-grading
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Make that ¥"normally open (NO).¥" (Thanks to gytabit¥'s URL for Tyco Electronics.)