Table 5.1: Pin Definitions
Pin
1
2
3
4
6
5, 9
Name
Description
+5
*
IRIGIN HI
Positive IRIGB input.
IRIGIN LOW
Negative IRIGB input.
+12
*
-12
*
GND
Ground for ground wires and shields.
* Consult the factory before using these power supply outputs.
The current drive for an IRIG-B
"
one
"
is 10 to 20 mA. The input circuit consists of a 56-
ohm resistor in series with the photodiode input of an optical isolator. The photodiode has a
forward voltage drop of about 1.8 volts. The input may be driven directly by the output of a
TTL-level driver with sufficient current capability. Inputs may also be driven in a current
loop from a higher-voltage driver.
The IRIG-B serial format consists of a one second long, 100 pulse code divided into fields.
The SEL-267D relay decodes the second, minute, hour and day fields.
When IRIG-B data acquisition is activated either manually (with the IRIG command) or
automatically, two consecutive frames are taken. The older frame is updated by one second
and the two frames are compared. If they do not agree, the data are considered erroneous
and discarded.
Automatic execution is invoked about once every five minutes, except near midnight on New
Year’s Eve. At this time IRIG-B data acquisition is halted so the system clock may imple-
ment the year change without interference from the IRIG-B clock.
This port accepts the demodulated version of the IRIG-B time code. An IRIG-B demodulator
(SEL-IDM) is available from SEL to convert a modulated IRIG-B into eleven sources of
demodulated IRIG-B.
Date Code 920326
Installation
SEL-267D Instruction Manual
5-5
Summary of Contents for SEL-167D
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