Figure 7: Analog Input Block Schematic Diagram - Honeywell ST700 User Manual

Figure 7: Analog Input Block Schematic Diagram

The OUT_SCALE is normally the same as the transducer, but if L_TYPE is set to Indirect
or Ind Sqr Root, OUT_SCALE determines the conversion from FIELD_VAL to the
output. PV and OUT always have identical scaling. OUT_SCALE provides scaling for
PV. The block places the value in OUT if the mode is AUTO. If MAN mode is allowed,
write a value to the output. The status prevents any attempt at closed loop control using the
MAN value, by setting the Limit value to Constant.
The LOW_CUT parameter has a corresponding "Low cut-off" option in the IO_OPTS bit
string. If the option bit is set as True, any calculated output below the low cut-off value
changes to zero. This is only useful for zero based measurement devices, such as flow. The
PV filter, whose time constant is PV_FTIME, is applied to the PV, and not the
FIELD_VAL.
Equations
FIELD_VAL = 100*(channel value - EU@0%) / (EU@100% - EU@0%) [XD_SCALE]
Direct: PV = channel value
Indirect: PV = (FIELD_VAL/100) * (EU@100% - EU@0%) + EU@0% [OUT_SCALE]
Ind Sqr Root: PV = sqrt (FIELD_VAL/100) * (EU@100% - EU@0%) + EU@0%
[OUT_SCALE]
Revision 2.0 FOUNDATION Fieldbus ST 700 Pressure Transmitter User's Guide Page 47