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

Bob Bownes bownes at gmail.com
Sun Jan 22 13:33:57 EST 2017

#5) Everyone likes blinkenlights. 

> On Jan 22, 2017, at 08:55, jimlux <jimlux at earthlink.net> wrote:
>> 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 reconfigure.
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