Cpu Load Calculation; Table 6-9. Execution Times - ABB Advant Controller 450 Product Manual

Advant Controller 450 Product Guide
Chapter 6 Technical Data and Performance

6.9 CPU Load Calculation

6-10
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.
examples of system load. The loads calculated are based on the execution times in
Type
(1)
DI 1 DB element DI
2 PC elements (AND gate w. 4 inputs)
DO 1 DB element DO, 2 PC elements AND(4)
AI 1 DB element for normal AI input, a Pt100 or
thermoc. input (incl limit check)
AO 1 DB element for a normal AO output
(incl. limit check)

Table 6-9. Execution times

Description
Table 6-10 provides some
Table 6-9.
Execution time
(ms)
0.005 (interrupt)
0.02 (cyclic)
0.02
0.25
0.2
3BSE 015 953R201 Rev B