Allen-Bradley 1747-SN - Page 158

Specifications A–5
Publication 17476.6 - July 1996
You need to calculate your T
dm–nbt
: the RIO throughput time from
when the input closes on the 1746-IN16 until the output on the
1746-OB16 is on.
1. Use the throughput formula to calculate the maximum
throughput.
T
dm–nbt
= 2T
ps
+ 2T
RIO
+ T
adp
+ T
SNo
+ T
SNi
+ T
id
+ T
od
T
ps
= 25.0 ms, which is from the APS reference manual (assume for
example)
T
RIO
= The total RIO scan time (ms)
T
SNo
= See value in the table on page A–13, T
SNo
without M0 File
Writes
(Normal Mode).
T
SNi
= 5.0 ms
T
id
= 10.0 ms, which is from I/O module instruction sheets
T
od
= 1.0 ms, which is from I/O module instruction sheets
T
dm–nbt
= 2(25.0) + 2T
RIO
+ 8.0 + T
SNo
+ 5.0 + 10.0 + 1.0
2. Calculate the total RIO scan time (T
RIO
). Locate the baud rate
(115.2K) and adapter size, which is found in the table on page
A–4. Multiply the RIO scan times listed under the 115.2K
heading by the number of each different type of rack that you
have. Add those numbers together:
T
RIO
= T
adapter 1
+ T
adapter 2
+ T
adapter 3
T
RIO
= 1(4.0 ms) + 2(5.5 ms) + 3(3.5 ms)
T
RIO
= 25.5 ms
3. Find T
SNo
on page A–13 in the table T
SNo
without M0 File
Writes (Normal Mode). For this example T
upd
> T
hold
, and there
are 4 logical racks configured. Therefore:
T
SNo
= 7.0 ms
4. Substitute all the values for variables in the throughput formula
and solve for throughput:
T
dm–nbt
= 2T
ps
+ 2T
RIO
+ 2T
bp
+ T
SNo
+ T
SNi
+ T
id
+ T
od
T
dm–nbt
= 2(25.0)+ 2(25.5) + 8.0 + 7.0 + 5.0 + 10.0 + 1.0
T
dm–nbt
= 132.0 ms = maximum throughput