1、 外文资料与中文翻译 外文资料： Intelligent thermal energy meter controller Abstract A microcontroller based, thermal energy meter cum controller (TEMC) suitable for solar thermal systems has been developed. It monitors solar radiation, ambient temperature, fluid flow rate, and temperature of fluid at various loca
2、tions of the system and computes the energy transfer rate. It also controls the operation of the fluid-circulating pump depending on the temperature difference across the solar collector field. The accuracy of energy measurement is 1.5%. The instrument has been tested in a solar water heating system
3、. Its operation became automatic with savings in electrical energy consumption of pump by 30% on cloudy days. 1 Introduction Solar water heating systems find wide applications in industry to conserve fossil fuel like oil, coal etc. They employ motor driven pumps for circulating water with on-off con
4、trollers and calls for automatic operation. Reliability and performance of the system depend on the instrumentation and controls employed. Multi-channel temperature recorders, flow meters, thermal energy meters are the essential instruments for monitoring and evaluating the performance of these syst
5、ems. A differential temperature controller (DTC) is required in a solar water heating system for an automatic and efficient operation of the system. To meet all these requirements, a microcontroller based instrument was developed. Shoji Kusui and Tetsuo Nagai 1 developed an electronic heat meter for
6、 measuring thermal energy using thermistors as temperature sensors and turbine flow meter as flow sensor. 2 Instrument details 1 The block diagram of the microcontroller (Intel 80C31) based thermal energy meter cum controller is shown in Fig. 1. RTD (PT100, 4-wire) sensors are used for the temperatu
7、re measurement of water at the collector field inlet, outlet and in the tank with appropriate signal conditioners designed with low-drift operational amplifiers. A precision semiconductor temperature sensor (LM335) is used for ambient temperature measurement. A pyranometer, having an output voltage
8、of 8.33 mV/kW/m2, is used for measuring the incident solar radiation. To monitor the circulating fluid pressure, a sensor with 420 mA output is used. This output is converted into voltage using an I-V converter. All these output signals are fed to an 8-channel analog multiplexer (CD4051). Its output
9、 is fed to a dual-slope 12-bit A/D converter (ICL7109). It is controlled by the microcontroller through the Programmable Peripheral Interface (PPI-82C55). Fig. 1. Block diagram of thermal energy meter cum controller. A flow sensor (turbine type) is used with a signal conditioner to measure the flow
10、rate. Its output is fed to the counter input of the microcontroller. It is programmed to monitor all the multiplexed signals every minute, compute the temperature difference, energy transfer rate and integrated energy. A real-time clock with MM58167 is interfaced to the microcontroller to time-stamp
11、 the logged data. An analog output (02 V) is provided using D/A converter (DAC-08) to plot both the measured and computed parameters. A 44 matrix keyboard is interfaced to the microcontroller to enter the parameters like specific heat of liquid, data log rate etc. An alphanumeric LCD display (24-cha
12、racter) is also interfaced with the microcontroller to display the measured variables. The serial communication port of the microcontroller is fed to the serial line driver and receiver (MAX232). It enables the instrument to interface with the 2 computer for down-loading the logged data. A battery-b
13、acked static memory of 56K bytes is provided to store the measured parameters. Besides data logging, the instrument serves as a DTC. This has been achieved by interfacing a relay to the PPI. The system software is developed to accept the differential temperature set points (Ton and Toff) from the ke
14、yboard. An algorithm suitable for on-off control having two set-points is implemented to control the relays. 3 Instrument calibration The amount of energy transferred (Q) is : Where = mass flows rate of liquid kg/s ； V = volumetric flow rate (l/h) ； = density of water (kg/l) ； Cp = specific heat (kJ
15、/kgC)； and T = temperature difference between hot and cold (C). The accuracy in energy measurement depends on the measurement accuracy of individual parameters. Temperature measurement accuracy depends on the initial error in the sensor and the error introduced due to temperature drifts in the signa
16、l conditioners and the A/D converter. The temperature sensor is immersed in a constant temperature bath (HAAKE Bath-K, German), whose temperature can be varied in steps of 0.1C. A mercury glass thermometer (ARNO AMARELL, Germany) with a resolution of 0.05C is also placed along with PT100 sensor in t
17、he bath. This is compared with the instrument readings. The accuracy of the instrument in temperature measurement is 0.1C. Hence, the accuracy in differential temperature measurement is 0.2C. The flow sensor having a maximum flow rate of 1250 l/h is used for flow measurement. It is calibrated by fix
18、ing it in the upstream of a pipeline of length 8 m. The sensor output is connected to a digital frequency counter to monitor the number of pulses generated with different flow rates. Water collected at the sensor outlet over a period is used for estimating the flow rate. The K-factor of the sensor i
19、s 3975 pulses/l. The uncertainty in flow measurement is 0.25% at 675 l/h. Uncertainties in density and specific heat of water are 0.006 kg/l and 0.011 kJ/kgC respectively. Maximum amount of energy collection (Q) = 6750.984.18415/3600 = 11.53kW. Uncertainty in energy measurement q/Q = (v/V)2 + (/)2 + (cp/Cp)2+(t/T )21/2.
