# A Fast Calibration Method for Sensors of Atmospheric Detection System
## 4 Evaluation
### VPSSD Method and Temperature Calibration Time Evaluation  
The temperature sensor used in the atmospheric detection system is a negative temperature coefficient thermistor. With glass encapsulation, the thermal conductivity is fast and the conditioning time is negligible relative to the calibration system. After a practical calibration test, the sensor resistance \(R_{0}=15.60\) K\(\Omega\) at 25 \({}^{\circ}\)C has a \(B\) value of 3718 and the relationship between resistance change and ambient temperature can be expressed as  
\[R_{NTC}=15.60\times\exp\left\{3718\left(\frac{1}{T}-\frac{1}{298.15}\right) \right\}. \tag{19}\]  
The hardware composition of the atmospheric sounding system temperature detection circuit is the same as that shown in Figure 4. The AD7/14 is used as the digital-to-analog converter chip with 24-bit detection accuracy, where \(R_{1}=200\) K\(\Omega\), \(R_{2}=100\) K\(\Omega\), \(V_{REF}=V_{CC}=2\) V, and \(C=0.01\)\(\mu\)F.  
During the calibration of the thermistor, the expected temperature calibration accuracy is \(\Delta T_{exp}=0.05\)\({}^{\circ}\)C. Record a set of data at intervals of 10 \({}^{\circ}\)C in the \(-80\)\({}^{\circ}\)C to 50 \({}^{\circ}\)C temperature range. The minimum temperature variation in the external environment that the ADC detection circuit can distinguish is between \(-80\)\({}^{\circ}\)C and 50 \({}^{\circ}\)C, as shown in Figure 10a. In the temperature range \(-70\)\({}^{\circ}\)C to 0 \({}^{\circ}\)C, the temperature resolution accuracy of the detection circuit is higher than \(\Delta T_{exp}\). The steady-state temperature error during calibration can be set according to \(\Delta T_{error}=\Delta T_{exp}\). In the temperature range \(-80\)\({}^{\circ}\)C, 10 \({}^{\circ}\)C to 50 \({}^{\circ}\)C, the temperature resolution accuracy of the detection circuit is lower than \(\Delta T_{exp}\). The steady-state temperature error during calibration can be set according to \(\Delta T_{error}=\Delta T_{ADC}\). The abscissa of the curve in Figure 10b is the calibration time, and the ordinate is the logarithmic steady-state error of the currently recorded resistance value of group \(q=30\). The \(\Delta T_{error}\) corresponds to each point in the curve, the steady-state error of the first 30 points of the point is less than \(\Delta T_{error}\). The steady-state error of the current control loop at different temperature points can be found in Figure 10b by matching the final steady-state error calibration required for the current system to the coordinate point in Figure 10a. The adjustment time of each control method for different steady-state errors is shown in Table 1. Combined with the \(\Delta T\) at each temperature point in Figure 10a, the \(\Delta T\) corresponding to \(-70\)-\(0\)\({}^{\circ}\)C is the smallest; so, the steady-state time is the longest. The \(\Delta T\) corresponding to 30 \({}^{\circ}\)C, 40 \({}^{\circ}\)C is smaller than 50 \({}^{\circ}\)C and bigger than \(-70\)-\(0\)\({}^{\circ}\)C; so, the steady-state time is  
Figure 10: (**a**) Detection accuracy of the ADC circuit at different temperatures. (**b**) Stabilization time of starting calibration at different calibration temperature points. longer than 50 \({}^{\circ}\)C but less than \(-\)70\(-\)0 \({}^{\circ}\)C. In general, the smaller the \(\Delta T\), the longer the steady-state time. Do not use the VPSSD method, calibrate every 10 \({}^{\circ}\)C in the range of \(-\)80-50 \({}^{\circ}\)C according to \(\Delta T_{exp}=0.05\)\({}^{\circ}\)C. The adjustment time of each control method at different temperature points is shown in Table 1. For TFB and Fuzzy PID control methods, their controller signal output cannot meet the requirements. Therefore, their steady-state time has no practical application value and is no longer analyzed.