The overall solution meter is a kind of civilian product, and the performance price ratio determines its market share. This requires our designers to fully consider the impact of device selection on product cost. Here, our overall solution is to install a meter in each space unit (such as each room). These meters are connected into a network system, and the community service company is responsible for the service and management of the network. The host computer of the network system can control the work of the meter and collect the data of each meter, and the community service company can charge the user according to the data. The fan coil temperature controllers used in the past are independent of each other and do not require data transmission and memory, so there are many products using analog circuits. The fan coil temperature control and thermal meter are not, it must use microprocessor technology. Here, we use ATMEL's 89C52 as the system CPU to complete all the work of the meter.
Detection of temperature signal In this system, NTC thermistor is used as the temperature detecting element (labeled as Rt), and the voltage drop (labeled as Ut) of a constant current source (labeled as n) varies with Rt, Ut The value can be obtained by A/D conversion, so that we can find the value of Rt by the following formula. Rt two Ut/It solves the nonlinear problem because the value of Rt is not linear with the temperature value. The problem to be noted here is that in order to eliminate the interference and also to stabilize the display of the system temperature data, the system collects the temperature data multiple times and obtains the average value as the current temperature data. Due to the volume limitation of the instrument and the cost reduction, the meter does not use a dedicated real-time clock chip. Instead, it uses the internal resources of the 89C52 in software programming and uses its timer T2 as the clock of the system.
If you select a 1.0592MH: crystal oscillator, the time constant of T2 is IFOOH, so the timer spell is interrupted every 62.sms, and the number of interrupts is counted in the T2 interrupt service routine, then 16 interrupts are 1 second. It should be noted here that the priority of the T2 timer interrupt should be set to the highest level to avoid system clock error caused by interference from other interrupt sources. Fan coil temperature control and thermal energy meter development were damaged or lost. In this system, serial EEPROM is used as the power loss memory of important data. Since various EEPROMs have a write life problem, we use the principle of fuzzy control to control the number of writes to the EEPROM, so that the number of writes is minimized without causing data errors due to power loss that may occur at any time.
The data shows that the system uses a specially customized liquid crystal display, which displays a large amount of information. The development of computer technology has made it possible to connect these scattered meters together to form a network. Here, the electrical protocol is connected using the MAX485 interface chip. Each meter has one and only one address in the system, and the software uses a broadcast communication protocol. The management computer (host computer) can choose to communicate with a meter separately, for example, if a meter is required to transmit thermal energy data, or a command to stop the user due to arrears, then the meter needs to return a set of messages in response. You can also choose to communicate with all meters, such as the system clock calibration. In this case, the communication is unidirectional and the meter does not need to respond. Software constitutes a good product, not only must have reliable hardware quality assurance, but also have good software to make the contact with the user the easiest and clearest. For this we have done a lot of work in software design. Development prospects In order to save energy, with the development of China's market economy, community-based centralized heating supply, quality service, and paid use will be more and more, the controllers without the previous billing function will withdraw from the market, and will be replaced by Cost-effective fan coil temperature control and thermal meter. Its development prospects are very promising.
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