Posted by: SATYASRINIVAS | January 19, 2015

Instrumentation: Detailed Engineering Question: IRIG-B(AM) or IRIG-B (TTL).

IRIG refers to the Inter-range Instrumentation Group.

The ‘formats’ of IRIG time codes are many, but the 3 most common formats are IRIG-B ( with significant share of the market), IRIG-A (Minimal market share), and IRIG-G (very little marker share).

IRIG time code signals may be:
(a) Unmodulated (DC level shift, no carrier signal)
(b) Modulated (amplitude-modulated, sine wave carrier).
(c) Modified Manchester (amplitude-modulated, square wave carrier).

The above with reference to IRIG-B application

(a) IRIG-B (TTL/DCLS): It is more common with New IED’s. It offers better resolution than IRIG-B AM But but cannot be used in runs of more than 100m (unless you use repeaters or optical outputs)

(b) IRIG-B AM: It is more common with older IED’s. Comapred with TTL case It is less accurate, But it can be run further than above. AM IRIG-B signals generally use coaxial cables, and most commonly BNC connectors. However, use of BNC connectors does not guarantee that it is an AM IRIG-B signal being used

IRIG-B AM is generally used in a larger power plant with master and slave clock system. With slave clock’s and BOP/Off-site PLC’s typically located more than 100m from DCS Room.

(c) Rarely used. Hence not discussed.

In summary “IRIG-B” alone does not adequately define protocol or electrical requirements. Specify AM IRIG-B or DCLS IRIG-B (or the full IRIG-B code) to be more specific. To be helpful, also specify the electrical requirements (desired voltage level) of the IED and to be really helpful, specify the connector type at the IED (BNC, screw terminal, DB9 etc).

For Detailed Information on IRIG-B kindly go to the refer this Technical Note.

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