<Appendix 3.
Arithmetic (Ar) Block>
256
IM 01E21A02-03EN
A3.2 Input Section
Thereareveinputs:INandIN_LOmaininputsandIN_1,IN_2,andIN_3auxiliaryinputs.
INandIN_LOareintendedtoconnectdeviceswithdierentmeasurementrangesandallow
the use of switching a measurement range by selecting the measuring device. However,
becausethereareslightdierencesbetweenINandIN_LOvaluesevenwhenthesameitem
is measured, instantaneous switching causes abrupt changes in the output. To prevent this
phenomenon, the Arithmetic block uses a function known as range extension to compensate
the IN and IN_LO values between RANGE_HI and RANGE_LO. This enables the input to be
switched smoothly. The result of the range extension function is substituted into PV to be used for
calculations.
A3.2.1 Main Inputs
The range extension function determines the PV value in the following order:
1. IfIN≥RANGE_HI => PV=IN
2. IfIN≤RANGE_LO => PV=IN_LO
3. IfRANGE_HI>IN>RANGE_LO=>PV=gxIN+(1-g)xIN_LO
g=(IN-RANGE_LO)/(RANGE_HI-RANGE_LO)
RANGE_HI and RANGE_LO are threshold values for switching two main inputs bumplessly.
RANGE_LO
PV = IN_LO PV=g 3 IN+(1-g) 3 IN_LO PV =IN
RANGE_HI
IN
Formula based on
(1) and (2)
(2): Range for IN
(1): Range for IN_LO
PVisaparameterwithstatusinformation,andPVstatusisdeterminedwiththevalueof“g”.
If“g”<0.5=>ThestatusofIN_LOisused
If“g”≥0.5=>ThestatusofINisused
The determination of the status is made with a hysteresis of 10% provided for 0.5.
IfRANGE_LO>RANGE_HI,thestatusesofPVandOUTare“Bad.CongurationError”.Then,
“CongurationError”.isoutputtoBLOCK_ERR.
Ifthemaininputisoneinput,theinputisreectedasis,RANGE_HIandRANGE_LOarenot
taken into account.
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