Safety Scanner for GuardPLC Controllers User Manual

1 Publication 1753-UM002A-EN-P - July 2005

Appendix

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)