WAGO I/O System 750
Process Image 29
750-482/000-001 2AI 4-20mA HART NAMUR NE43
Manual
Version 1.0.2
4
Process Image
Mapping of process data in the process image of fieldbus systems
The representation of the I/O modules’ process data in the process image
depends on the fieldbus coupler/controller used. Please take this information as
well as the particular design of the respective control/status bytes from the
section “Fieldbus Specific Design of the Process Data” included in the description
concerning the process image of the fieldbus coupler/controller used.
Evaluation of Status Byte
Some fieldbus systems can process status information of process value by
means of a status byte.
This status byte can be displayed via the commissioning tool
WAGO-I/O-
CHECK
.
However, processing via the fieldbus coupler/controller is optional, which means
that accessing or parsing the status information depends on the fieldbus system.
The HART I/O module provides the fieldbus coupler/controller with a different
amount of process data depending on the operating mode set.
For pure 3.6 mA … 21 mA analog values the HART module transmits 16-bit
measured values and optionally 8 status bits on each channel.
The digitalized measured value is transmitted to the process image of the
coupler/controller in a data word (16 bits) as an input byte 0 (low) and input byte
1 (high).
This value is mapped with a resolution of 13 bits on Bit B2 ... B14.
Status information, which can be evaluated in the event of a fault, is contained in
the two least significant bits (B0 and B1). If the measurement is above the
measuring range, Bit B0 is set = 1, and if the measurement is below the
measuring range or if a wire breaks, Bit B0 and B1 are set = 1.
The input voltage range for the measured values of 3.6 mA to 21 mA is scaled to
the numerical range from 0xFCFF to 0x7FFD.
