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IRIG-B Primer
C.2
Connecting the IRIG-B Output
The Model 1133A comes equipped with one, high drive, IRIG-B output connector using screw
terminals. Terminal connectors are compatible with twisted pair cabling. If using a coaxial cable,
you can easily transition from the two wires (coming from the back of the 1133A) to a BNC
connector using a BNC Breakout.
NOTE: If using a shielded, twisted-pair cable (e.g. Belden 8760), connect the cable shield to
the clock ground lug.
C.2.1
Screw Terminals
Prepare the twisted pair cable by stripping back at least 1/4 inch of the insulation and any shielding;
NO NOT tin the bare wire with solder. Tighten the screws down on the wire.
C.2.2
How Far Can I Run IRIG-B Cabling?
Some important considerations for transmitting IRIG-B over long distances are: (1) resistive
losses in cabling, (2) electromagnetic interference, (3) propagation delays and (4) installation and
maintenance costs.
Additional Information on Using IRIG-B
1. For details on distributing IRIG-B signals over long distances, see application note, AN101,
Distributing Timing Signals in a High-EMI Environment. Download the file:
appnote101.pdf
2. For important considerations about IRIG-B connections, distribution of signals and accuracy,
download the file:
IRIG-B accuracy and connection requirements.pdf
C.2.3
Synchronizing Multiple IED’s From One Masterclock Output
In many installations, master clock signals (e.g. from the 1133A) are “fanned out” to a number
of devices. This method makes more efficient use of the clock synchronizing capability since the
clock drivers are designed to handle multiple loads. The exact number of possible loads must be
determined from the input impedance of each connected IED. For example, if the input impedance
of the IED is 5 kilohms, determine the device current (I) drawn as derived in Calculation C.1.
(C.1)
I
=
V
÷
Z
= 5
V olts
÷
5000
Ohms
= 0
.
001
Amps
(1
mA
)
If you were to connect ten of the same IED’s to the same output, then the total current drawn
would be 10 x 0.001 A = 0.01 A (10 mA).
1
Model 4969 and 4970, Pomona Electronics, 9028 Evergreen Way, Everett, WA 98204, 800-490-2361,
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