# Active Two-Wire Temperature Sensor Schematic Circuit Diagram

#### Innovative Measurement Technique: Amplifying Remote Sensor Signals

In typical scenarios where a physical quantity must be measured remotely, it’s usually essential to incorporate an amplifier with the sensor. However, this necessitates a separate power supply, leading to the requirement of an additional wire for the sensor. The circuit presented here cleverly addresses this challenge by utilizing the same two lines for both measurement and power supply. This is achieved by converting the measured current, buffered by IC1a, into an additional supply current drawn from the current source, IClb. Essentially, the input voltage level can be determined by observing the magnitude of the supply current. This current includes not only the opamp’s consumption but also, potentially, the sensor’s current draw.

#### Precision and Compensation: Managing Current Deviations

When employing the specified sensor and opamp, the current typically measures around 0.7 mA (0.65 mA with a 5 V supply, 0.7 mA at 10 V, and 0.77 mA at 15 V). Considering a full-scale deflection (FSD) of 10 mA, this represents a deviation of approximately 7%, a factor that can be conveniently compensated. Despite this deviation, the circuit offers an innovative and efficient method of amplifying remote sensor signals, enhancing the accuracy of measurements without requiring an additional power line.

#### Efficient Temperature Measurement: Current Variation Strategy

In this circuit configuration, the temperature sensor induces a change in supply current ranging from 0.7 mA to 10.7 mA, corresponding to a temperature shift from 0 °C to 100 °C. A moving coil ammeter incorporated into the supply line simplifies temperature readings significantly. The adjustment screw on the meter allows the nullification of the opamp’s supply current (0.7 mA), streamlining the temperature reading process.

#### Addressing Voltage Drop Challenges: Compensation and Power Supply

It is crucial to compensate for voltage drops across lengthy lines by employing a higher supply voltage. This measure ensures that IC1 and IC2 receive adequate power (at least 5 V) to prevent them from being underpowered. An ammeter, serving as a measuring instrument for electric current in a circuit, features low resistance and is connected in series with the load to gauge the electric current flowing through it.

#### Digital Ammeter Innovations: Shunt Resistor and Calibration

In digital ammeter designs, a shunt resistor is utilized to generate a calibrated voltage proportional to the current flow. This voltage is then measured by a digital voltmeter via an analog-to-digital converter (ADC). The digital display is meticulously calibrated to exhibit the current passing through the shunt, offering a precise and digital representation of the measured current.

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