Emerson ControlWave Instruction Manual page 30

ControlWave I/O Expansion Rack Instruction Manual
Calculating the
Maximum Current
Required
2-18
Figure 2-12. Wiring Field Power to the PSSM
Use the following formula to determine the maximum current required
for the +24 Vdc bulk power used with a particular ControlWave I/O
Expansion Rack:
Max Bulk +24 Vdc Supply Current = CPU
:
where
CPU
max_current
Σ
I/O Module
max_current
So, for example, if you have a ControlWave I/O rack with a 16AI
module, an 8AO module, and a 32DI module, the maximum current
draw is 1A for the CPU plus 2A for the 16AI module plus 1A for the
8AO module and 1A for the 32DI module, for a total of 5A.
This calculation covers current draw during normal operation
Note:
(steady state) as well as the current draw during power-up in-
rush when the unit is first powered on. Power up in-rush current
can last up to 100 milliseconds and is higher than the current
draw required during normal operation.
Refer to Table 2-2 for ControlWave steady state and loop current
requirements for bulk power supplies.
max_current
refers to the maximum current required by the CPU (with or
without an SCB), backplane and the PSSM. This is 1A.
refers to the sum of the maximum current required by each
and every I/O module installed in the unit. The amount per
I/O module varies as follows:
16 AI Module
8 AI Module
8 AO Module
16 DI Module
32 DI Module
16 DO Module
32 DO Module
6 UDI Module
4 RTD Module
6 LLAI Module
Installation
Σ
+ I/O Module
max_current
2A per module
1A per module
1A per module
1A per module
1A per module
See table (no surge current)
See table (no surge current)
See table (no surge current)
See table (no surge current)
See table (no surge current)
Revised Aug-2015