Rockwell Automation 1753-DNSI DeviceNet Safety Scanner for GuardPLC Controllers - Manual (Page 117)

1 Publication 1753-UM002A-EN-P - July 2005
Appendix
D
Calculate Safety Connection Bandwidth
This appendix provides equations for calculating the amount of
system bandwidth consumed by an individual safety input or output
connection.
In the equations below,
• RPI is in milliseconds
• data sizes are in bytes
• Baud_Rate is in bits per second
The bit_stuffing_factor is the percentage of bandwidth estimated to be
used by bit stuffing. We used 15% for our calculations.
Single-cast Inputs 1 to 2 Bytes
In the equation below:
A = 1
÷ Data_RPI ÷ 0.001
B = Safety_Data_Size + 6
C = (B x 8 x bit_stuffing_factor) rounded to the nearest whole number
D = 1
÷ (Data_RPI x 100) ÷ 0.001
%Bandwidth = 100 x {[A x (57 + B x 8 + C) + (D x 115)]
÷ Baud_Rate}
3 to 250 Bytes
In the equation below:
A = 1
÷ Data_RPI ÷ 0.001
B = (2 x Safety_Data_Size) + 8
C = (B
÷ 8) rounded to the nearest whole number
D = 1
÷ (Data_RPI x 100) ÷ 0.001
E = (B x 8 x bit_stuffing_factor) rounded to the nearest whole number
%Bandwidth =
100 x
( {A x [(57 x C) + (B x 8) + E] + (D x 115)}
÷ Baud_Rate )