Rockwell Automation Allen-Bradley ControlLogix B Series User Manual

30 Rockwell Automation Publication 1756-UM542A-EN-P - September 2014
Chapter 4 Time Synchronization
1756HP-TIME Module as an IRIG-B Slave
The 1756HP-TIME module can synchronize to an external IRIG-B source using
coaxial cable. The source needs to output IRIG-B 122 format time.
You can also use the 1756HP-TIME module to output 1588 PTP and NTP
w
hile receiving time from an IRIG-B source.
CST and UTC Time Conversion
This process is not needed for RSLogix 5000 software version 18.00.00 or later.
The 1756HP-TIME module can also be used to convert CST or UTC time
fo
rmats to Gregorian time (year, day, month, and so on). The GPS module
accurately tracks the local CST and UTC time to the current Gregorian time.
Therefore, the different drifting rates of the CST are also compensated for.
In a sequence-of-events (SOE) solution, the SOE module (for example, the
1756-I
B16ISOE module) reports the event time in either CST or UTC time
formats.
These values are passed to the 1756HP-TIME module (by using unconnected
messa
ge blocks) and converted to Gregorian time. The 1756HP-TIME module
tracks the last 12 hours of CST, UTC, and Gregorian time formats. If an event
has occurred, you have up to 12 hours to convert the event time. See
CST/UTC
Conversion Message Blocks on page 37 for these message formats.
The CST offset can also be used to adjust the wallclock by using a set system
v
alues (SSV) instruction to pass the CST offset.
IMPORTANT
The current year for the IRIG-B format is not supported by the 1756HP-TIME
module. Therefore, you need to supply the current year in the output image of
the module in RSLogix 5000 software. A simple rung of ladder logic increases
the year without your intervention.
IMPORTANT
If using PTP as an output, you must also supply the UTC offset in the output
image. The current value is 35, but this changes periodically. To keep up to
date, this page lists the current value.
http://en.wikipedia.org/wiki/Leap_second.
IMPORTANT
If the 1756HP-TIME module has an IRIG-B time source that is accurate to 1 ms,
then the synchronization accuracy when using 1588 PTP is also limited to 1ms.
IMPORTANT
One CST master clock must be present for a sequence-of-events solution.
Verify that there is no duplicate CST master clock. This is indicated in 1756HP-
TIME module and the Logix controller.

Rockwell Automation Allen-Bradley ControlLogix B Series Specifications

General

Brand	Rockwell Automation
Model	Allen-Bradley ControlLogix B Series
Category	Control Unit
Language	English