Accurate, low-power remote detection concept

The remote detection examples shown here have the characteristics of high reliability, easy connectivity and ultra-low power consumption. These circuits are mainly for industrial environments that require stable communication and limited battery maintenance. This solution combines the research progress of low power consumption and high-precision amplification in recent years, and has the same low power consumption and high reliability wireless Mesh network function. Supporting these solutions are the zero-drift, low-input bias amplifiers LTC2063 and LTP5901-IPM. The former runs at 2 ?A and the latter consumes less than 1.5 ?A in sleep mode. The power consumption of these devices is low enough to be powered by a battery composed of copper and zinc electrodes (four square inches each) and an electrolyte formed by the inner substance of a lemon.
Wireless Mesh Network
Measurements performed and retrieved through wireless networks in an industrial environment rarely require high speed, but they usually require high reliability and safety, in addition to low-power operation, in order to extend the operating time of the battery to the limit. LTP5901-IPM forms a node or a SmartMesh? IP Mote in the 802.15.4e wireless network. LTP5901-IPM integrates a 10-bit, 0 V to 1.8 V ADC, and a built-in ARM? Cortex?-M3 32-bit microprocessor, which can be tested by simple programming. This terminal is used to achieve safety, reliability, low power consumption, flexibility and programmability.
Four detection applications
In general, the following circuit designs do not require advanced rocket knowledge. However, they are clean, efficient, and customized for specific applications. These designs do not need to be complicated. In fact, complicated designs will only increase cost and reliability risks.
The input of each circuit contains a sensor, and the output voltage is generated by processing the sensor output. Using the LTP5901-IPM 10-bit ADC as the input, each circuit attempts to map the input, covering most of the range between 0 V and 1.8 V.
Basic battery voltage detection

Figure 1. Simple battery voltage detection.
Figure 1 shows a typical non-inverting overall gain negative feedback op amp configuration that can detect partial pressure. The ADC range of the LTP5901 input is 0 V to 1.8 V. R1 and R2 reduce the battery voltage with the quiescent current to extend the battery life. The input bias current of LTC2063 is very low, even these high resistance values will not affect the accuracy of the final 10-bit ADC. The supply current consumed by the LTC2063 provides the advantage of zero drift over time and temperature.
  Current Detection

Figure 2. Current detection circuit.
The outstanding feature of battery-powered and isolated electronic equipment is that it can be grounded at any position. In a convenient circuit topology, we can detect current without losing versatility, and at the same time place the terminal in any position related to the local ground. For unipolar currents, such as 4 mA to 20 mA industrial loops, one can use traditional low-side topologies to safely detect currents related to local grounding. Figure 2 shows that the current flows through a very small resistor R2, which generates a detection voltage. This input voltage may be very small because of the amplifier's zero-drift, extremely low offset voltage performance and other reasons. The circuit shows that the gain of the input generated by the 501 mΩ sense resistor is increased by 101 V/V. At 20 mA, VOUT is 1.012 V. You can choose other values to use the ADC's 1.8 V range.
Resistance R4 is relatively low, which is a low impedance shunt for LTC2063 input capacitance. Therefore, the interaction between the larger R1 feedback resistance and the input capacitance will not stabilize.
After the circuit is optimized, it is used to test the mapping range of 0 mA to 35 mA current and 0 V to 1.8 V ADC.
irradiometer

Figure 3. Short-circuit irradiance measurement using solar cells.
The circuit shown in Figure 2 can also be used to measure the short-circuit current of a solar cell. In the short-circuit current mode, the current of silicon and other solar cells has a highly linear relationship with irradiance. The short-circuit current is the current of the 0 V solar cell. The circuit in Figure 3 does not guarantee that the solar cell will accurately reach 0 V when the current is current; however, even if it is 20 mA in full sunlight, the voltage is only 10 mV. The 10 mV level on the solar cell is actually a short circuit on its I-V curve.
We can use transimpedance amplifier (TIA) as an alternative. TIA can force the solar cell to reach 0 V and measure the current. The problem with this circuit is that in the entire irradiance range, the operational amplifier provides current to the solar cell. If it is important to reduce power consumption for the remote detection circuit, it is not feasible to provide 20 mA to the battery by the operational amplifier.
Considering the need to maintain close to 0 V, a small sense resistor should be used. The detection of a remote, battery-powered small voltage once again shows the need to use a high-precision, low-power power amplifier, such as LTC2063.
This type of physical layout is required for solar installations, that is, a wireless Mesh network that needs to implement zero temperature drift measurement. Fortunately, under short-circuit conditions, silicon photodiodes are relatively stable with temperature changes. For large installation sites where the ambient temperature is constantly changing, using LTC2063 and LTP5901-IPM, coupled with silicon solar cells, a simple and reliable design is an ideal solution.
Use thermocouple to measure temperature

Figure 4. Thermocouple detection circuit.
The thermocouple voltage can be positive or negative. The circuit shown in Figure 4 uses a micropower reference voltage source and a micropower amplifier to detect extremely small positive and negative voltages. Fortunately, if the thermocouple is electrically isolated from the device under test (DUT), it can be placed in any convenient voltage domain. The example in Figure 4 uses the LT6656-1.25, biasing the thermocouple at 1.25 V. The circuit output is a high-gain version of a small thermocouple voltage based on a 1.25 V reference voltage source. For this configuration, the ADC range of 0 V to 1.8 V is quite reasonable. If a zero-drift, low-offset amplifier is not used, extremely high gains of around 2000 V/V cannot be achieved.
  in conclusion
Very low power consumption, accurate remote detection is feasible. The examples in this article show that it is quite simple to combine low-power, high-precision amplifiers with programmable system-on-chip wireless Mesh nodes.