Retrofit or software for already designed machine:
If the input signals and the output signals are already defined, then the inputs are assigned to function groups. The function groups for a system are defined in the SELMO structure.
System as a whole: All inputs that are relevant for the entire system are assigned here. The operating modes and the monitoring of plant-relevant parts take place at this level. As an example, this usually means "system on/off, emergency off active, main fuses, power supply", etc. These signals are assigned to the system part. A matrix of bits, used for display and evaluation in the logic, is assigned. If no bit is set in this matrix, the system part is OK.
The system also consists of one or more hardware areas.
The hardware area is an area that divides the system into sub-areas. For example, the protected areas, access guarding, area-related voltage supplies, etc. are assigned to this area. These signals are assigned to the hardware area. A matrix of bits, which is used for display and evaluation in logic, is assigned. If no bit is set in this matrix, the hardware area is in order and the area can be operated according to the operating mode.
The hardware area consists of one or more stations.
Stations are units that are basically controlled logically by a step chain. The station has a matrix of bits that is assigned to station-related signals. There are two types of bits. Those that are monitored step-independently and those that are monitored step-related. The step-independent bits are, for example, circuit breaker signals or air monitoring. These are set directly in the matrix and shown in the step chain on the display. The step-related bits are set and displayed depending on the step and manual operation.
In this way, all real inputs in the system are assigned to the corresponding functional areas. Each function area has a clear function and reacts to the bits that are set in the matrix.
If no bit is set in the matrix of the unit, this stands for "everything is ok". Only then can the subordinate unit function. If a bit is set, it is displayed in plain text and the user interface informs the operator to the exact bit.
If no bit is set in the hardware area, then the subordinate stations can function at all. If a bit is set, it is displayed in plain text and the user interface informs the operator to the exact bit.
If no bit is set in the station, the operating window is displayed in blue and it is possible to switch to automatic mode. If a bit is set by a step-independent bit, then no manual movement or action can be carried out and it is not possible to switch to automatic mode. If a step-related bit is set, then a suitable step can be searched for via the step increment function - or the necessary signals are set via manual actions. The station processes the real signals that are necessary for the logical sequence.
At this level, SELMO uses zones to connect the bits that are bit-oriented from assemblies such as cylinders, keys, etc. with the defined steps. If modules are required that react to HMI inputs or are present as analogue values, then these are discretised by driver functions. This ensures that each signal is defined as a bit of a zone. A cylinder, for example, has two signals. These are additionally checked as a pair check, because the two signals must never be switched at the same time. A simple bit such as a button is always checked for the status 0 and 1 - exactly when it should be 1 and when it should be 0.