I have a question for the experts of this forum:

Can someone explain with examples in detail what is IRIG Time code? Where & how is it/can be used? I have already checked wiki where it explains the IRIG time code but not the applications.

Thanks in advance,
Ritika

 

IRIG time codes are often used by radio clocks to set/synchronize the date and time on other devices. It predates standards such as the 1 PPS output from many GPS receivers. It is common to achieve accuracies as close as one micro-second with systems such as IRIG-B.

A radio clock might be used to set the time and date at an RTU, to maintain synchronization across wide areas, and so on.

In general, wherever isochronous time is required, it is common to see radio/atomic clocks with IRIG-B outputs.

 

Ritika ... IRIG refers to the Inter-range Instrumentation Group. Specifically, IRIG publishes documents, and the one your interested in is IRIG-200, last updated in 2004 ... and is thus 'formally' called IRIG-200-04 (if you Google IRIG-200, you'll find lots of places to DL the document).

The 'formats' of IRIG time codes are many, but the 3 most common formats are IRIG-B (a 1 KHz signal with 95% of the market), IRIG-A (1 10 KHz signal with 4% of the market), and IRIG-G (a 100 KHz signal with about 1% of the market).

These signals come in two variants, a sin-wave signal with AM modulation and a pulse variant with pulse width modulation. The sin-wave variant is the MOST common, with the pulse width variant used for strip-chart applications.

All data is encoded as Binary Coded Decimal (BCD) and the "frames" of data are 1 second long for IRIG-B, 100 ms long for IRIG-A, and 10 ms long for IRIG-G.

All variants are continuous and contiguous ... no gaps or 'packeting'.

The most common place IRIG time codes are used are in instrumentation applications such as telemetry and engine test stand environments. They use it because you can get nanosecond clarity on 'events' and in telemetry and instrumentation, it's imperative to be able to analyze data between two (or more) asynchronous environments.

Vendors who are big into IRIG time codes include Brandywine and Symetricom (I have no financial interests in either). My knowledge comes from 30 years in telemetry ... I work in telemetry and as a part-time job, teach it (see ttiedu dot com, course 171 ... that's me).

If this does not answer your question adequately, you can drop me a line at tim dot 737 at gmail dot com.

cheers
tpg

 

Hi,

I would like to know if the IRIG-B time code transmission path is unidirectional? Is there any way to affect a higher-hierarchy time server via an IRIG connection? I have looked for articles regarding this but to no avail.

Thanks.
CYT

 

Hi,

IRIG-B is Unidirectional. Some GPS Clocks can act as a slave and be synchronized using IRIG-B. For instance the TCG 01 GPS Clock can be synchronized using TTL DC IRIG-B with IEEE1344 Extensions. It is also able to be ordered with NTP/ SNTP time server outputs.

BR,
MG

 

So, IRIG is basically used to sync time continuous between multiple wired devices?

Why not have a internal clock in each device and check the clock periodically.

 

SKS,

Take any combination of watches--they can even be the same model from the same manufacturer, set them all to exactly the same time, and carry/wear them around for a few days and then compare the time shown on each watch. You don't even have to carry/wear them around--just leave them in the same place for a few days.

Write back and tell us the results of your test.

You may have found a very inexpensive solution for a very universal problem. If so, we'd all be very grateful for the new information.

Thanks! We look forward to hearing back from you!!!

 

Why did the U.S. military never think of this? Why have a standard that makes every clock the same when you could just radio out to every remote installation in the entire world and ask them to synchronize their clock with your central clock?

> So, IRIG is basically used to sync time continuous between multiple wired devices?

> Why not have a internal clock in each device and check the clock periodically.

 

Pie,

Why not just have a single system that broadcasts a single time signal that is available to any receiver that wishes to synchronize their clock(s) with a universal clock?

Why have to send a request to have every remote installation to synchronize their clocks with a central clock? When you can just make the central clock's time available to anyone whenever they want to synchronize their clock--or to keep their clock synchronized to the central clock at all times?

 

You'll have to excuse my poor internet sarcasm. I work in power transmission and am well-aware of the advantages of using IRIG.