Automatic meteorological station MS&E-3RD
Design, development and test of AMC MS&E-3RD is in the period from 1994 to 1995, It is based upon a version MS&E-3R, developed during years 1992-1994 on the basis of MS&E-2. This is the third generation of AMC formed by companies in the composition of the Consortium "MS&E". The reason for its creation was the need to automatically determine the class of stability of the atmosphere in Pasquill, a parameter required for the operation of several diffusion models.
I.    Block diagram and working principle of AMC MS&E-3R
AMC MS&E-3R is composed of unit - electronics, sensors, power supplies, FM radio station and antenna. In the electronics block there are three separate modules: Analog module, Microprocessor controller module and Digital VHF communication.
The analog module converts with a very small mistake analog signals from sensors into digital signals. The original self-test system of Consortium "MS&E" used in MS&E-3R ensure reliable operation and maintenance of uncertainty in measurements for ambient temperature of -25°C to +60°C.
Microprocessor controller controls the analog module and modules for telecommunications. System software implemented in this module follows the recommended by the World Meteorological Organization (WMO) algorithms for measurements of AMC and primary data control.
Digital VHF communication module provides data transfer and remote control of AMC.
To be determined Class of stability of the atmosphere in Pasquill, it should be added additional sensors or based on existing to use a suitable algorithm for its determination.
Block diagram of MS&E-3R
II.     Method of determining the class of Pasquill.
The chosen method is known in literature as "Sigma-theta method". Unlike conventional methods, based on different empirical relationships between wind speed and intensity of solar radiation at the earth surface and atmospheric dispersion coefficients, at Sigma-theta method directly is measured the fluctuation of wind direction. Then is calculated the dispersion of such fluctuation.
Advantages of the method are:
- Using sensors that do not require frequent maintenance (instrument measuring solar radiation require daily cleaning of the receiving surface);
- More correct from a physical point of view (measuring value which is directly characterizing the atmospheric turbulence).
Disadvantages of the method are:
- Need for "quick" microprocessors to enable in real-time to calculate the statistical moments of the first and second order of the wind direction;
- At the time of application, the method mentioned by the International Atomic Energy Agency (IAEA), as one possible theory. This requires its protection in the first check missions of NPP "Kozloduy".
III. Realization of the method - AMC Model MS&E-3RD
By processing of the system software of AMC MS&E-3R is achieved realization of the method Sigma-theta. The algorithm is implemented so that it has reached calculation of  the statistical characteristics of wind direction in real-time. The data on the dispersion of wind direction is added to the generated output of AMC MS&E-3RD and recorded in the database of meteorological computer.
Subsequent checks on ASMM of NPP, built by AMC model MS&E-3RD by IAEA experts and discussions, led to the fact that in recent documents of the IAEA, concerning the meteorological providings of NPP, method Sigma-theta is recommended as the most appropriate ( Safety Standards Series No NS-G-3.2, IAEA, 2002) to determine the class of Pasquill.