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Models 5843, 5844, 5843S and 5844S
RS-232 or TTL
3.3
NUMBER OF REPEATS
In a loop configuration, the number of units that can be used as repeaters must be determined. A
repeater is any unit that uses the repeat function of the Link/Repeater. All Slaves in a Master/Slave
loop are considered repeaters. Three factors must be considered in calculating the maximum
number of repeaters possible in a loop; the data rate (bits per second), the minimum required width
of the original pulse echoed back to the Master, and the peak operating temperature.
N u m b e r o f R e p e a ts in a L o o p C o n fig u ra tio n *
1 00 0
10 0
1 0
1
1
3.3.1
Effects of Data Rate
The number of repeaters is an inverse linear function to the data rate (more repeats at
lower data rates). The data rate, or bits per second rate, determines what the original pulse
width of each bit will be. The higher the data rate, the smaller the pulse width of each bit.
As the signal passes through a repeater, any distortion effect on the data signal is greater at
higher data rates due to smaller pulse widths then lower data rates.
3.3.2
Pulse Width Distortion
As the data signal is passed from repeater to repeater, there is a small change to the pulse
width defined as pulse width distortion. The amount of change that is tolerable corresponds
to the percentage of original pulse width required by a particular communication system
design. Typically, a communication system requires the data word, or bit stream, that each
Slave IED receives, match the signal originally generated by the Master, within some
tolerance of pulse width distortion.
distortion, therefore, more repeats are tolerated. Conversely, low tolerance systems allow
fewer repeats in the loop.
10
D a ta R a te s (k b p s )
FIGURE 10. Number of Repeats
High tolerance systems allow more pulse width
3-3
10 0
10 00
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