AI measured value transport
The following chapters describe the output of the Value PDO (measured value output of the analog input channel, Analog Input = AI). This analog channel supports the following PDOs:
Floating point output (Real32), default setting: "Floating Point (Real32)" (default setting of the channel)
During commissioning, the channel reports its analog measured value as a plain text-readable floating point value, both readable in the TwinCAT configuration
as well as in the PLC Online View:
The Real32 PDO can simply be linked to a REAL variable in PLC:
This type of transmission avoids scaling errors, as the channel itself takes into account the measuring range (including any changes to the measuring range); commissioning and troubleshooting are significantly simplified compared to INT16.
Even if no unit (V, A, Ω, ..) is formally transmitted, the SI unit corresponding to the measurement context must be used, i.e. [A] and not [mA] for a 20 mA input.
Integer output (fixed point, INT16 or SINT16): "Standard (INT16)"
The channel reports its measured value as a 16-bit fixed point value (default incl. sign, signed integer), related to FSV (full scale value).
The value range extends over -32767 ...0 ... 32768, knowledge of the measuring range is required for interpretation and transformation on the control side, e.g. 10V ~ x7FFF = 32767 in legacy representation.
If the channel is to be linked with existing PLC code, it can be converted to this INT16 format. Otherwise, the default setting "Real32" is recommended.
With this type, the channel provides the AI status, see the following section.
Integer output (fixed point, INT16 or SINT16): "Compact", without PDO status
Corresponds to the previous point, but without PDO AI status.
This option is supported for compatibility reasons and results in minimal data consumption in EtherCAT. However, operation without status makes diagnosis more difficult.