# Classification of Systems and Maintenance Models
## 7 Results  
Radar systems emit electromagnetic waves, also known as radio waves. The waves are reflected by most objects, enabling the radar system to detect them. To achieve the best possible outcome, it is imperative to ensure that the radar transmitter generates a signal with precisely the right amount of power and specific characteristics. The radar transmitter power supply plays a critical role in its performance. To ensure that the radar system meets the necessary performance standards, it is vital to maintain a stable power supply.  
Let us define a subgroup of systems to which the power supply of the radar transmitter belongs. The power supply unit can be repaired, indicating a system maintainability sign of \(i=1\). The power supply is in continuous operation, displaying a temporary system use mode with the sign \(l=1\). Failures in the power supply, scheduled maintenance, and unscheduled repairs can all result in downtime. Therefore, the sign of failure's consequences is \(j=3\). And, finally, it is not possible to make an economic evaluation of the failure's consequences (\(k=1\)). Thus, we can associate the radar power supply with subgroup \(I_{1311}\), as presented in Table 1. According to this table, the achieved availability is the maintenance effectiveness metric.  
In the next step, we need to identify a specific subgroup of maintenance models, which is essential for determining the achieved availability. If a power supply failure is detected, it is turned off and shipped for repair. Instead, a spare power supply is connected resulting in a value of the classification sign \(a=1\). According to regulations, CBM with regular inspections must be conducted, resulting in a value of the classification sign \(b=2\). During the repair process, the power supply unit will be fully restored in a repair shop, resulting in a value of the classification sign \(c=1\). Determining power supply failure requires an instrumental inspection, which leads to the value of the sign being \(d=1\). Thus, the maintenance model falls under subgroup \(M_{1211}\).  
The output voltage of the power supply for the radar transmitter represents the system state parameter [97]. If the output voltage is less than 25 kV, the power supply is operable, that is \(FT=25\) kV. The parameters of the random process (125) are as follows: \(a_{0}=19.92\) kV, \(m_{A1}=0.01\) kV/h, \(\sigma_{A1}=0.0043\) kV/h, and \(\mu=0.9\). Assume that the random measurement error of the system state parameter has a normal distribution with a standard deviation of \(\sigma_{y}=0.5\) kV and a zero mathematical expectation.  
The following data were used to calculate the achieved availability: \(T=\)1000 h, \(t_{ins}=3\) h, \(t_{PR}=5\) h, and \(t_{CR}=10\) h.  
Consider the case of a periodic inspection schedule with an optimal threshold \(RT^{opt}\) for all inspection instants. In this case, the optimization criterion corresponds to (124).  
When calculating mean times (65)-(69), we set \(t_{n}=n\tau\), \(t_{k}=k\tau\), \(t_{j}=j\tau\), and \(t_{N}=N\tau\).  
Figure 4 shows the dependence of the achieved availability on the number of inspections in the interval (0, 7). By solving the problem (124), we obtain the following solution: \(RT^{opt}=23.5\) kV, \(\tau_{opt}=200\) h, \(N_{opt}=4\), and \(A_{a}^{r}\big{(}\tau_{opt},\ RT^{opt}\big{)}=0.976\).  
For CM inspections, that is, at \(RT=FT=25\) kV, the following solution is optimal: \(N_{opt}=9\), \(\tau_{opt}=100\) h, and \(A_{a}^{r}\big{(}\tau_{opt},\ FT\big{)}=0.94\). Thus, the use of the optimal replacement threshold \(RT^{opt}<FT\) substantially increases the achieved availability and reduces the number of inspections by more than half. It should be noted that the unavailability when using CBM inspections is 2.5-fold less than when using CM inspections.  
A further increase in the achieved availability is possible using criterion (120), which assumes a sequential schedule of inspections with an optimal replacement threshold value for each inspection moment.