Emerson Rosemount OCX8800A - Page 200

Priority
number
Priority description
1 An alarm condition with a priority of 1 is recognized by the system, but
is not reported to the operator.
2 An alarm condition with a priority of 2 is reported to the operator, but
does not require operator attention (such as diagnostics and system
alerts).
3-7 Alarm conditions of priority 3 through 7 are advisory alarms of
increasing priority.
8-15 Alarm conditions of priority 8 to 15 are critical alarms of increasing
priority.
8.10.4 Block execution
The arithmetic function block provides range extension and compensation
through nine arithmetic types.
There are two inputs (IN and IN_LO) used in calculating PV. PV is then combined
with up to three inputs (IN_1, IN_2, and IN_3) through the user selected
compensation function (ARITH_TYPE) to calculate the value of func. A gain is
applied to func., and then a bias is added to get the value PRE_OUT. In AUTO,
PRE_OUT is used for OUT.
Range extension and calculation of PV
When both IN and IN_LO are usable, the following formula is applied to calculate
range extension for PV:
PV = G * IN + (1-G) * IN_LO
(G has a range from 0 to 1, for IN from RANGE_LO to RANGE_HI.)
8.10.5
Compensation input calculations
For each of the inputs IN_1, IN_3, and IN_4, there is a gain and a bias. The
compensation terms (t) are calculated as follows:
• When IN_(k) is usable: t(k) = GAIN_IN(k) * (BIAS_IN(k) + IN_(k))
• When IN_(k) is not usable, then t(k) gets the value of the last t(k) computed with
a usable input.
Status handling
• IN_x Use Bad
• IN_x Use Uncertain
• IN_LO Use Uncertain
• IN Use Uncertain
F
OUNDATION
™
Fieldbus Manual
December 2022 00809-0500-4880
200 Emerson.com/Rosemount