On 11/8/21 8:24 PM, Matt Huszagh wrote:
I'm still trying to understand how heavy pieces of equipment are
supposed to be supported within a 19" rack. Here's what I understand so
far. There seem to be basically three options, the first two being more
"official" than the third.
The first option is that support rails are fastened to the rack in holes
oriented 90 degrees relative to the normal front and back mounting
holes. I've attached a photo that shows this, stolen from
. I'm
not endorsing the non-metal screws here, but this is the best picture I
could find that illustrates the concept.
These are called "rails". The module is placed on these rails. Then,
flanges attached to the front of the instrument are fastened to the
holes on the front of the rack. The rails support most of the weight
instead of the front flanges. From the front it only looks like the
instrument is attached to the rack from the flanges; the rails are not
visible. These rails additionally do not take up any "rack unit" space,
so that one instrument can be placed immediately below or above another.
The second option is that the instrument is somehow fastened to "slides"
that are capable of supporting the instrument weight. These seem nice
but are more expensive. I won't discuss this further since I don't know
much about it yet.
The third option is to use a shelf that attaches to all 4 posts of the
rack on the front and back facing fastening holes. Then, the equipment
simply sits on this shelf (these shelves sometimes support being pulled
out). When using sufficiently heavy-duty shelves (e.g., the black box
RM399 that Dave mentioned), multiple instruments can be stacked on top
of each other, all supported by the same shelf. This seems like the
somewhat less "official" solution but nonetheless works. One difficulty
with it is that you can only remove the top-most instrument of a shelf.
Is this a correct assessment?
More or less. First, there's nothing more or less "official" here; these are all perfectly valid and common approaches. And there's also cantilevered mount, which is when the rack mount ears of the mounted device support the entire weight of the device.
I like option 1 (well option 2 as well, but that seems a bit more
complicated and probably quite a bit more expensive). My difficulty with
this is that I'm having trouble finding suitable rails (to use the above
terminology). NavePoint sells these server rack rails:
But, the problem with them seems to be that they mount to the front and
back of the rack. The instrument flange (or "ears") would then need to
mount over these. So, when you unfasten the flanges to remove the
instrument you lose the rail support. One way around this would be to
simply rest the instrument on the rails and not fasten the
flanges. That's probably ok.
This is a very common approach for stationary applications, not fastening the ears if the unit is otherwise supported.
Rack slides are less common for test equipment than for computer equipment. Rack slides typically cost hundreds of dollars, and must be specifically supported by (i.e., designed for use with) a given piece of equipment. Rack slides usually come in two pieces: the part that is screwed to the unit, an the part that's screwed into the rack. Sometimes there's a third "floating" piece in the middle, but that's not as common as it used to be. There are many variations, some of which work well, and some, not so much.
Modern server-class computer equipment manufacturers, in particular, seem to take great delight in making their rack slides incompatible with those of their competitors, and even with their own, from model to model and from generation to generation. It is a racket. (heh, get it? ;))
The terminology is very flexible, mainly because these things are so damn common, and have been for so many years, across so many different industries. People come up with their own unofficial terms ("ears") and they stick, and some eventually become a part of the vernacular.
Slides, rails, shelves, and ears are the terms that you will likely hear the most often in this context. Sometimes people use "rails" and "slides" interchangeably.
There are also variations, like shelves that mount on slides. There are also other neat accessories, like drawers (actual drawers, like for tools, cables, or...well, underwear) that are rack-mounted.
In the context of test equipment, I suggest that you not get your heart set on slides. They're less common in that world than in some others, they're difficult to find, and they're very expensive. One reason they're difficult to find is that warehouse grunts pull instruments (or computers) out of racks and leave the rack-side parts of the slides in the racks, and auction off the unit with half of the slides still screwed to the unit.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
Dave McGuire