SM-Universal Encoder Plus User Guide
69
Issue Number: 6
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The transmission delay is a factor of the cable used. The following table gives examples
of m/s transmission characteristics of three different cable types.
The following table give the maximum delay for each baud rate as well as the
approximate maximum cable length for cables with specific metre per second
transmission characteristics (neglecting data set-up delay):
Clock output - line attenuation
Assuming a model for a basic performance screened cable of 60m
Ω
and 250pF per/m
and the minimum generator and receiver specifications (for one to one installations
using RS485), the approximate maximum frequency (baud rate) per cable length is
given below:
A standard cable would allow improved performance.
Cable
Transmission
m/s
A
2.78 x 10
8
B
1.78 x 10
8
C
1.33 x 10
8
Frequency
(Baud rate)
Maximum
delay
Approximate maximum cable lengths
A
B
C
100 kHz
5
µ
s
694 m
445 m
331 m
200 kHz
2.5
µ
s
347 m
222 m
165 m
300 kHz
1.66
µ
s
231 m
148 m
110 m
400 kHz
1.25
µ
s
173 m
111 m
82 m
500 kHz
1
µ
s
138 m
89 m
66 m
1 MHz
500 ns
69 m
44 m
33 m
1.5 MHz
333 ns
46 m
29 m
22 m
2 MHz
250 ns
34 m
22 m
16 m
Length
Time constant
Maximum frequency (Baud rate)
10
2.97 x 10
-9
150 MHz
50
7.14 x 10
-8
6 MHz
100
2.73 x 10
-7
1.5 MHz
150
5.87 x 10
-7
651 kHz
200
1.00 x 10
-6
363 kHz
250
1.50 x 10
-6
230 kHz
300
2.08 x 10
-6
158 kHz
350
2.72 x 10
-6
115 kHz
400
3.43 x 10
-6
87 kHz
450
4.19 x 10
-6
68 kHz
500
5.00 x 10
-6
54 kHz