ABB AC 31, Technical Manual

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Annexes
Annexes - Page 12
ABB Control - AC 31
1SBC 260400 R1001-b 06.99
4. Historical values
Historical values are central unit specific internal variables which enable memorizing a
functions intermediate results required for numerous cycles.
In fact, certain functions require the results obtained during cycle N-1 so that cycle N will
execute correctly (for example: the PI and PIDT1 controllers).
The total number of available historical values, in the 40 and 50 series central units, is 256.
The functions and the number of historical values which they use are given in the following
table:
Timer functions
ASV 1 (supplementary memory for the timers limited to 42 variables)
ESV 1 (supplementary memory for the timers limited to 42 variables)
MOA 1 (supplementary memory for the timers limited to 42 variables)
MOK 1 (supplementary memory for the timers limited to 42 variables)
PDM 1 (supplementary memory for the timers limited to 42 variables)
TOF 1 (supplementary memory for the timers limited to 42 variables)
TON 1 (supplementary memory for the timers limited to 42 variables)
TP 1 (supplementary memory for the timers limited to 42 variables)
Counter functions
CTU 2
CTUH 2
VRZ 3