Rockwell Automation T8019 Trusted Process Control Algorithm Software Package - Manual (Page 8)

Trusted
TM
Process Control Algorithms T8019
Issue 8 Sep 07 PD-T8019 8
1.1. Functions
1.1.1. Square Root Extraction
SQRTX
PV
OUT IP
MAX
IP
MIN
The Process Variable (PV) is scaled to a value 0…1 according to maximum input value (IP
MAX
) and
minimum input value (IP
MIN
). Out of range values will result in the value being clamped to the range,
i.e. a value greater than maximum input will use the IP
MAX
value, similarly a value below the minimum
will use the IP
MIN
value. The square root of the resulting value is then taken and is returned as a
percentage.
i.e.
( ) ( )
100
IP - IP
IP IP , IP PV, Max Min
OUT
MIN MAX
MIN MAX MIN × =
Note: All inputs (PV, IP
MIN
and IP
MAX
) and the returned value OUT must be real.
If IP
MAX
< IP
MIN
, the function assumes that the values have been reversed and “swap” the values. The
“reversed” error counter is incremented each time the function has to swap the parameters.
If IP
MAX
= IP
MIN
, the function returns a value of zero and increments the “zero divide” error counter to
indicate that a divide by zero error would have occurred.
If PV is not a number (NaN), the function returns a value of zero and increments the “Param” error
counter.
All input range parameters (IP
MIN
and IP
MAX
) must be finite, i.e. not ±infinities or NaNs. Behaviour is not
defined for any other values.
If PV is not a NaN, and an overflow or underflow condition occurs the function returns zero and
increment the corresponding error counter.