ABB Advant Controller 450 Product Guide

Advant Controller 450 Product Guide
Chapter 6 Technical Data and Performance
6-10 3BSE 015 953R201 Rev B
6.9 CPU Load Calculation
To estimate the CPU load in Advant Controller 450, the following should be considered:
• About 4% of the total capacity of Advant Controller 450 should normally be reserved for
cyclically executed basic system functions; priority handling, system supervision etc.
• About 20% of the total capacity should be reserved for event controlled functions,
AdvaCommand functions, communication etc.
• The remaining 76% capacity is then available for cyclically executed functions,
AMPL programs, process I/O, logs and data set communication.
The formula for calculating the CPU load for several identical functions is:
CPU load in% = (N x T / Tc) x 100 where
N = number of functions (for example, control loops), T = function execution time (ms)
and Tc = function cycle time (ms).
When calculating the CPU load, the system has duties other than merely executing PC
programs. For example, the processing of analog signals involves the following operations:
• Conversion of analog input signals from transducer signals to process related units.
• Linearization of input value.
• Checking of input value against limit values.
• Handling of error conditions.
• Conversion of analog output signals from a process quantity to an actuator signal and
checking of limits.
Table 6-9 provides some typical values of execution times, to be used for load estimates.
They are primarily intended to check if a system will be close to the maximum load or not.
The examples chosen represent functions of normal complexity. Table 6-10 provides some
examples of system load. The loads calculated are based on the execution times in Table 6-9.
Table 6-9. Execution times
Type Description
Execution time
(ms)
DI
(1)
1 DB element DI
2 PC elements (AND gate w. 4 inputs)
0.005 (interrupt)
0.02 (cyclic)
DO 1 DB element DO, 2 PC elements AND(4) 0.02
AI 1 DB element for normal AI input, a Pt100 or
thermoc. input (incl limit check)
0.25
AO 1 DB element for a normal AO output
(incl. limit check)
0.2

ABB Advant Controller 450 Specifications

General

Brand	ABB
Model	Advant Controller 450
Category	Controller
Language	English