West Control Solutions KS98-1 - Manual (Page 143)

III-7.10 2OF3 ( 2-out-of-3 selection with mean value formation (No. 38))
Function 2OF3 forms the arithmetic mean value of input variables x1, x2 and x3.
The difference of x1, x2 and x3 is formed and compared with parameter Diff. Inputs the value of which exceeds
this limit value are not used for mean value formation. With 1 applied to fail1...fail3 (e.g. the fail signals of
AINP), faulty inputs are not taken into account either for mean value formation. err1 = 1 indicates that 1 input failed
and was not used for mean value formation. If at least 2 inputs do not participate in mean value formation, output
err2 is set to 1. With input off set to 1 or if output err2 = 1 the x1 value is output at y1.
With more than 3 input variables, function 2OF3 can be cascaded.
Output Casc indicates the number of values used for mean value formation. This is important with 2OF3 function
cascading.
With unwired factor inputs ( x1mult...x3mult) factor 1 is used automatically. If one of inputs x1...x3 is not
used, the relevant x-mult must be set to 0.
The x-mult input of the following function block is wired with factor output Casc of the previous function block.
Example of cascading
Selecting and storage 9499-040-82711
III-143 2OF3 ( 2-out-of-3 selection with mean value formation (No. 38))
]
err1
err2
Diff fail1
fail2
fail3
off
X1
X1mult
X2
X2mult
X3
X3mult
Y1
Casc
Fig. 8 Cascading example