[time-nuts] purpose of time of day display units

jimlux jimlux at earthlink.net
Sun Jan 22 08:55:39 EST 2017

On 1/21/17 10:31 PM, Ruslan Nabioullin wrote:
> Hi, looking at pictures of various time metrology equipment setups for
> best practices and inspiration, I have commonly seen time of day display
> unit(s) installed in racks containing processing or time transfer
> equipment, e.g.,
> http://www.xyht.com/wp-content/uploads/2015/05/Powers_Master_Clock.jpg.
> All that these units do is merely display the time of day and sometimes
> the date, typically by means of seven segment LED displays, of the time
> code inputted to them (typically IRIG-B, I'm guessing).

There's a few reasons I can think of:
1) the display is also a distribution amplifier of some sort - one time 
source going into rack, distributed to things in the rack (or the next rack)

2) as phk commented, it lets you know that your time code isn't broken 
(i.e. someone got in behind the rack and disconnected the wrong cable)

3) It's a crude visual check - your eye/brain is pretty good at catching 
a change in the pattern of blinky lights.  IN this situation, you'd 
expect all the displays to change simultaneously.

4) the equipment configuration "just growed" from a collection of 
smaller ones, each with its own display.

We put displays like this in all of our ground support equipment (GSE) 
racks when doing spacecraft or subsystem tests, mostly for reason #2 and #4.

You might have a GSE rack or two in the lab when you're building up the 
subsystem.  Someone else's subsystem has their rack, also with a 
timecode display.   When you bring the two subsystems together for 
integration, you bring the racks with them, and it's not worth it to 

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