<8. Detailed Description>
● Language Characteristics and Selection
• Characteristics of FBD and LD
In FBD and LD, data connections and inter-function-block connections are
represented as signal lines, which enables easy visualization of data flow, as well as
inter-block relationships. FBD and LD languages are thus ideal for programming
regulatory control of analog signals.
FBD and LD differ in that FBD handles all data as variables, while LD represents
BOOL-type data using contacts and coils embedded in ladder circuits.
Therefore, among the application examples described earlier, those not using
BOOL-type data, namely, “1. Example of Single-loop NPAS_PID“, “2. Example of
Single-loop NPAS_PID with CAS connection to NPAS_PG_L30_BP“, “3. Calculation
Example“ are identical in LD and FBD.
On the other hand, as can be seen from “3. Calculation Example”, “Conditional
Example 1” and “Conditional Example 2,” even simple calculations and conditionals
are not intuitively represented in FBD and LD. A conditional represented using Jump
function and Return jump looks complicated.
For all the above reasons, FBD and LD are not suitable for programming
calculations, and especially conditionals.
• Characteristics of ST
In ST, applications are coded as text so data connections and inter-function block
connections are represented using “:=”. As such, it does not allow easy visualization
of the data flow, as well as inter-block relationships.
However, as calculations and conditionals are coded as text, it allows intuitive
understanding of even complex calculations.
For the above reasons, ST is not suited for programming regulatory control of
analog signals but is well-suited for programming applications that involve
calculations and conditionals.
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