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Precision And Low Power Remote Sensing Concept,Did You Understand That??

Auth:亿配芯城 Date:2019/11/18 Source:www.yibeiic.com Visit:25 Related Key Words: Low power consumption High precision Bias amplifier
This solution combines low power consumption in recent years、Research progress in high precision amplification,Equal low power consumption、High reliability wirelessMeshInternet function。Support for implementing these solutions is zero drift、Low input bias amplifierLTC2063withLTP5901-IPM,The former is the highest2μACurrent operation,The latter consumes less current in sleep mode1.5μA。The power consumption of these devices is low enough,Even a copper and zinc electrode can be used(Every four square inches),And a battery-powered combination of electrolytes formed from the internals of lemon。
 

01

wirelessMeshThe internet

 

Measurements implemented and retrieved over a wireless network in an industrial environment rarely require high speed,But they usually require high reliability and security,Also requires low power operation,To maximize battery run time。LTP5901-IPMin802.15.4eForming a node or a wireless networkSmartMesh®IP Mote。LTP5901-IPMIntegrated one10Bit、0Vto1.8V ADC,And a built-inARM®Cortex®-M3 32Bit microprocessor,Can be tested by simple programming。This terminal is used for security、reliability、Low power consumption、Flexibility and programmability。
 

02

Four detection applications

 

In general,The following circuit designs do not require deep rocket knowledge.。but,They are neat、Efficient,Is customized for specific applications。These designs don't need to be complicated;Actually,Complex design only increases cost and reliability risks。

 

One sensor per input in the circuit,Output voltage by processing sensor output。useLTP5901-IPM 10BitADCAs input,Each circuit tries to map the input,cover0Vto1.8VMost of the range。

 

03

Basic battery voltage detection

 

Figure1Demonstrates a typical in-phase overall gain negative feedback op amp configuration,Can detect partial pressure。LTP5901InputADCRange is0Vto1.8V。R1withR2Reduce battery voltage with minimal quiescent current,To extend battery life。LTC2063Input bias current is very low,Even if the above two resistance values ​​are high, it will not affect the final10BitADCAccuracy。LTC2063Minimizes supply current,Provides zero drift advantages over time and temperature。

 

Figure1:Simple battery voltage detection

 

04

Current Detection

 

The beauty of battery-powered and isolated electronics lies in:It can be grounded at any position。In the most convenient circuit topology,我们可以in不丧失通用性of情况下检测Current,Also place the terminal in any location related to local grounding。Unipolar current,E.g4mAto20mAIndustrial loop,One can use traditional low-side topologies to safely detect currents associated with local grounding。Figure2Shows that current flows through a very small resistorR2,Resulting in a detection voltage。Because of the zero drift of the amplifier、Very low offset voltage performance and other reasons,This input voltage can be very small。In the circuit shown in the figure,via501mΩThe gain of the input generated by the sense resistor is increased101 V/V。在20mATime,VOUTYes1.012V。You can choose other values ​​to get the most out of it.ADC的1.8Vrange。

 

Figure2:Current detection circuit

 

resistanceR4Relative resistance is relatively low,YesLTC2063Low-impedance shunt for input capacitor。therefore,Large resistanceR1The interaction between the feedback resistor and the input capacitor does not stabilize。

 

The constructed circuit is optimized,For testing0mAto35mA电流、0Vto1.8V ADCMapping range。
 

05

Irradiance meter

 

Figure3The circuit shown can be used to measure the short circuit current of a solar cell。In short circuit current mode,The current and irradiance of silicon and other solar cells are highly linear。Short circuit current is0VSolar cell current。Figure3The circuit in the circuit does not guarantee that the solar cell accurately reaches the maximum current.0V;but,Even in full sunlight, the current is20mA,The voltage is only10mV。On a solar cell10mVLevel in itI-VActually short circuit on the curve。

 

Figure3:Short-circuit irradiance measurement using solar cells

 

我们可以以互阻放大器(TIA)作为替代。TIA可以强制让太阳能电池达到0V,并测量电流。这种电路存在的问题在于,在整个辐照度范围内,都是由运算放大器为太阳能电池提供电流。如果对于远程检测电路,最重要的是最小化功耗,那么由运算放大器为电池提供20mA是不可行的。

 

考虑到太阳能电池需要保持接近0V,实际设计中应使用一个小型检测电阻。不过对位置遥远、由电池供电的小电压实施检测表明,电路中需要采用高精度、低功耗的功率放大器,例如LTC2063。

 

太阳能装置所需的就是这类物理布局,即需要实施零温度漂移测量的无线Mesh网络。幸运的是,在短路条件下,硅光电二极管随着温度的变化相对稳定。对于环境温度不断变化的大型安装场地而言,采用LTC2063和LTP5901-IPM,再加上硅太阳能电池,所构成的简单且可靠的设计是非常理想的解决方案。
 

06

采用热电偶测量温度

 

热电偶电压可以是正压也可以是负压。图4所示的电路融合采用微功率基准电压源和微功率放大器来检测极小的正负电压。幸运的是,如果热电偶与被测器件(DUT)电气隔离,则可以置于任何方便的电压域中。图4中的示例使用LT6656-1.25,在1.25V时偏置热电偶。电路输出是基于1.25V基准电压源的小热电偶电压的高增益版本。对于这种配置,0V至1.8V的ADC范围相当合理。如果不使用零漂移、低失调放大器,则无法实现2000 V/V左右的极高增益。

 

图4:热电偶检测电路
 

07

结论

 

极低功耗、精准的远程检测绝对是可行的。本文的示例显示,将低功耗、高精度放大器与可编程片上系统无线Mesh节点相结合是相当简单的。

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