ADI AD7793热电偶测量系统解决方案
发布时间：2011-10-27 22:57
发布者：Liming
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ADI公司的 AD7792/3是高精度测量系统的低功耗低噪音模拟前端(AFE),包括三个差分模拟输出的低噪音16/24位Delta-Sigma ADC,仪表放大器能直接连接到ADC,增益设定为64,4.17Hz的噪音为40nV,工作电压2.7-5.25V, 主要用在热电偶测量,RTD测量,气体分析,工业过程控制,手持仪表,血液分析以及6位DVM等.本文介绍了AD7793主要特性,方框图, RTD和热电偶测量电路图以及采用AD7793 24位Sigma-Delta ADC完整的热电偶测量系统电路图和材料厂清单. The AD7792/AD7793 are low power, low noise, complete analog front ends for high precision measurement applications. The AD7792/AD7793 contain a low noise 16-/24-bit Σ-Δ ADC with three differential analog inputs. The on-chip, low noise instrumentation amplifier means that signals of small amplitude can be interfaced directly to the ADC. With a gain setting of 64, the rms noise is 40 nV when the update rate equals 4.17 Hz. The devices contain a precision low noise, low drift internal band gap reference and can accept an external differential reference. Other on-chip features include programmable excitation current sources, burnout currents, and a bias voltage generator. The bias voltage generator sets the common-mode voltage of a channel to AVDD/2. The devices can be operated with either the internal clock or an external clock. The output data rate from the parts is software-programmable and can be varied from 4.17 Hz to 470 Hz. The parts operate with a power supply from 2.7 V to 5.25 V. They consume a current of 400 μA typical and are housed in a 16-lead TSSOP package. AD7793主要特性: Up to 23 bits effective resolution RMS noise 40 nV @ 4.17 Hz 85 nV @ 16.7 Hz Current: 400 μA typical Power-down: 1 μA maximum Low noise programmable gain instrumentation amp Band gap reference with 4 ppm/°C drift typical Update rate: 4.17 Hz to 470 Hz 3 differential inputs Internal clock oscillator Simultaneous 50 Hz/60 Hz rejection Programmable current sources On-chip bias voltage generator Burnout currents Power supply: 2.7 V to 5.25 V –40°C to +105°C temperature range Independent interface power supply 16-lead TSSOP package Interface 3-wire serial SPI®, QSPI™, MICROWIRE™, and DSP compatible Schmitt trigger on SCLK AD7793应用: Thermocouple measurements RTD measurements Thermistor measurements Gas analysis Industrial process control Instrumentation Portable instrumentation Blood analysis Smart transmitters Liquid/gas chromatography 6-digit DVM 
图1.AD7793方框图 
图2.采用AD7792/3的RTD应用电路图 
图3.采用AD7792/3的热电偶测量电路图 采用AD7793 24位Sigma-Delta ADC完整的热电偶测量系统 Complete Thermocouple Measurement System Using the AD7793 24-Bit Sigma-Delta ADC The circuit, shown in Figure 4, is a complete thermocouple system based on the AD7793 24-bit sigma-delta ADC. The AD7793 is a low power, low noise, complete analog front end for high precision measurement applications. The device includes a PGA, internal reference, internal clock, and excitation currents, thereby greatly simplifying the thermocouple system design. 
图4.带冷端补偿的热电偶测量系统电路图(简化电路图:所有的连接和去偶电容未标) 
图5. 热电偶测量系统外形图 
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