State-Zone Modelling (SZM)

<< Click to Display Table of Contents >>

Navigation:  Welcome to SELMO  > Method > The control example > Formal specifications >

State-Zone Modelling (SZM)

 

 

The automation table is extended by some symbols in the SZM so that the display on the HMI can also be modelled. The entire input vectors are not considered, but the individual input signals. The signals E1 and E2 result in a pair of signals because they describe an actuator and thus can only ever occur mutually. A signal pair can also be generated from signal E3. An additional zone is generated by setting signal E3 to 0. This ensures in the sequence that the transition is only carried out when the E3 key is released.

 

In the table, the diagnostic behaviour is assigned to the input signals according to the states. The states are listed in the row and the zones in the columns. This is where the term state-zone modelling comes from. Each input signal is assigned a matrix bit Mx and, if necessary, a pair check bit Px. The system is extended by the outputs Zx, Mx and Px, as these are used for status indication on the HMI. The outputs Zx are to provide the operator with information about the current state, about the following states and the states already passed through.

 

As described under point 4, this is a sequence control. From the control section, the input signals are fed to the control unit via sensors and, together with the state of the control unit, resulting in the outputs through the corresponding switching of the states. The sequence is exactly predefined, i.e. from Z1 is changed to Z2 by fulfilling the defined transition conditions and so on.

 

In the table, the input E1, as well as the two inputs E2 and E3 generate the zones. According to the state of the control device, the target state of the input is determined by:

 

2 Here the corresponding output is controlled so that a signal change takes place and at the interface, to the operator, the corresponding matrix bit is set to 1 so that it is indicated which input signal is expected.

1 Here, the input signal must be set to 1, otherwise, an error will be diagnosed in the control path.

0 The "don't care" rule applies here.

 

 

 

 

Diagnostic behaviour (S,I,0) for instantaneous input signals, matrix bit, pair check bit

Instantaneous state, instantaneous output y(k)

E1, M1,P1

E2, M2,P2

E3, M3

NeuesElement230, M4

Z1 „Wait button“

1

0

2

0

Z2 „Cylinder in front, A1

0

2

0

2

Z3 „Wait button“

0

1

2

0

Z4 „Cylinder back“, A2

2

0

0

2

Table 7-4 State-Zone Model Table

 

The inputs E1 and E2 sit on the cylinder and are therefore to be treated as belonging together. The cylinder is always in one of the positions. Only during movement (defined as S) is none of these positions occupied. If both inputs E1 and E2 occur at the same time, an error condition occurs in the control section. Such a unit (such as the cylinder) is checked for "pair check" and thus leads to an error condition. This error is output to the HMI by means of the Px at the interface to the operator.

 

The E3 button is also viewed in two contiguous zones. In this way, a defined state of the key is achieved in the Zx states. The pair check can be neglected because in physical reality a signal can't be 0 and 1 at the same time.

 

 

 

NeuesElement264

 

 

 

The view of the operator or user of the control system must also take into account the outputs to the user via the human-machine interface, as shown in Figure 1-1. In this way, the outputs of the system are extended and should always give the user the best possible information about the current state of the system. In case of an error, the user must be informed about the cause of the error. This can only be guaranteed if the informal and formal specification is extended to include the user's point of view.