Rockwell Automation T8019 Trusted Process Control Algorithm Software Package - Manual (Page 12)

Trusted
TM
Process Control Algorithms T8019
Issue 8 Sep 07 PD-T8019 12
2. Function Blocks
2.1. Analogue Scaling
SCALE
PV
OUT
IP
MAX
IP
MIN
OUT
MAX
OUT
MIN
LIMIT
The scale function linearly scales the input value (PV) according to the low input (IP
MIN
), high input
(IP
MAX
), low output (OUT
MIN
) and high output (OUT
MAX
) values. The input value is clamped to the range
IP
MIN
to IP
MAX
. I.e. a PV value less than IP
MIN
results in the IP
MIN
value being used, similarly a value
greater than IP
MAX
results in the IP
MAX
value being used). The output (OUT) value varies linearly
between OUT
MIN
and OUT
MAX
as the input (PV) varies between IP
min
and IP
MAX
. The LIMIT output is to
indicate that the input value (PV) is out of range, i.e LIMIT = IP
MIN
>PV>IP
MAX
, LIMIT is set TRUE if PV
is out of range.
IP
MAX
, IP
MIN
, OUT
MAX
and OUT
MIN
are typically constants but may, in practise, use any analogue or
register value.
( ) ( )
( )
MIN MIN MAX
MIN MAX
MIN MAX MIN OUT OUT OUT
IP - IP
IP IP , IP PV, Max Min
OUT + × =
Note: PV, IP
MAX
, IP
MIN
, OUT
MAX
and OUT
MIN
have to be of type REAL, the result (OUT) is returned as
type REAL and LIMIT is of type BOOLEAN.
If IP
MAX
< IP
MIN
, the function is to assume that the values have been reversed and “swap” the values.
Similarly, if OUT
MAX
< OUT
MIN
the two values are to be swapped. In both cases, the “reversed” error
counter is to be incremented each time the function has to swap the parameters. All range parameters
(IP
MAX
, IP
MIN
, OUT
MAX
, OUT
MIN
) must be finite, i.e. not ±infinities or NaNs. Behaviour is not defined for
any other values.
If IP
MAX
= IP
MIN
, the function is to set OUT to OUT
MIN
, LIMIT to FALSE and increment the “Zero Divide”
error counter to indicate that a divide by zero error would have occurred.
If PV is a NaN, the function is to set OUT to OUT
MIN
, LIMIT to FALSE and increment the “Param” error
counter. If PV is not a NaN and overflow or underflow conditions occur during the execution of the
function, the function is to set OUT to OUT
MAX
or OUT
MIN
respectively, LIMIT to FALSE and increment
the corresponding error counter. If both overflow and underflow conditions occur, the function is to set
OUT to OUT
MIN
, LIMIT to FALSE and increment both corresponding error counters.