Glossary · Automation fundamentals, platforms and components
Operand
German: Operand
In programming, an operand is the value, variable or address on which an instruction or operator acts, for example the input I 0.1 in an AND instruction or the variable Speed in the expression Speed * 2.
- Automation components
In one sentence
An operand is the value, variable or address an instruction or operator acts on, such as an input bit in an AND instruction.
Example
In the instruction list line AND I 1.3, AND is the operator and I 1.3 is the operand.
How it applies
- Engineering: Operands can be constants, variables, inputs, outputs or memory addresses. Their data type must match the operation.
- Maintenance: Cross-reference lists show where each operand is used, which helps find the cause of unexpected states.
- Documentation: Use symbolic operand names with comments in programs, and keep them consistent with I/O lists and circuit diagrams. Documentation that refers to program operands should use the same names.
- Commissioning: Monitoring operand values online shows why a condition is not fulfilled.
Operand vs. operator
The operator is the operation (AND, ADD, compare); the operand is what it operates on. In PLC terminology, "operand" is also used loosely for addressable memory areas such as inputs, outputs and markers.