In principle, a pair of strain target flow meters are respectively installed on the rising pipe and the falling pipe according to the thermohydrodynamics, and the flow meter is installed on the hydrodynamics channel or the return pipe (the installation position of the flow meter is different, and the final measurement result is also different). The flow meter sends out the differential signal proportional to the total flow, and a pair of temperature sensors get the digital signal expressing the high and low temperature, The data signals from the total flow and temperature sensors are collected by the integrator, and the heat output of the heat exchanger system software is calculated by using the integration formula.

The principle of application of target flowmeter has always been a disadvantage. In North China, urban and rural residents generally charge for central heating according to the total area of housing rather than the specific amount of heating, which leads to poor users' concept of environmental protection and energy conservation, and leads to serious waste of resources. Obviously, the method of measurement and verification is not reasonable. In the early 1980s, the application of thermal meters in capitalist countries such as Bray America was very extensive. Thermal companies used thermal meters as the basis and method of billing and charging, with environmental protection and energy saving of 20% - 30%. As a basic countermeasure for energy-saving buildings, the Ministry of housing and urban rural development of the people's Republic of China has included the measurement and verification fees for heat generation into the Ninth Five Year Plan for building energy conservation and the 2010 plan: in the work of installing heat meters and related adjustment of machinery and equipment for industrial buildings with centralized heat supply within the scope of target flowmeter and verifying the fees according to the household measurement, the Ministry of housing and urban rural development of the people's Republic of China has achieved actual results according to the demonstration sites in 1999 and just started marketing and promotion, 2001 It was implemented in the residential quarters under construction in the most important cities in 2012. The water meter can be divided into two types according to the way of marking: large number e type and pointer c type, while large number e type: the marking situation composed of pointer and word wheel; pointer c type: the marking situation of pointer. The reading values of these two water meters are all carried out according to the following methods.

The way of big number e type is to find whether the base around the pointer close to the wheel is x0.1 or x0.01. What he expresses is the amount of water that each cell of the pointer means, so its upper position is 10 times of his, and the next cell of the pointer is 0.1 times of his. That is to say, all the numbers are 10 carry!

Pointer type C: for all water meters with pointer, see how many times the base mark around the pointer is, that is, the amount of water that the pointer does not go through a small file format is several times that of 1 cubic meter. Look for the pointer position of x1. If it goes through a small grid, it means 1 cubic meter, and then it is 0.1 times that of the pointer. If it goes forward, it means 10 times that of the pointer, the derivation will know.