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To do this you need a differential amplifier, but there are two problems will occur when connecting this amplifier to the output of the bridge: the loading effect and changing the gain. The output of the previous circuit is calculated by subtracting Vb+ and Vb- and then amplifying the result to be readable. The values of Wheatstone resistors had chosen to limit current flow and to increase linearity of the output. To solve this issue you can use a Wheatstone Bridge, an electrical circuit used to measure an unknown electrical resistance by balancing two legs of a bridge circuit, to get rid of the DC offset and to increase output sensitivity. This operation can be done using a voltage divider, but for a specific range of 80 to 150 ohms (-51.85 to 129.87 degrees C) the divider has a DC offset which will decrease the sensitivity when amplifying this voltage. The first part of the circuit is about converting the resistance change of PT100 to a voltage change so the Arduino can read it. This instructable shows a full guide of how to use a RTD with Arduino, it uses a two wire PT100 RTD, an Arduino, 3 LM741 operational amplifiers, and resistors. The RTD wire is a pure material, typically platinum, nickel, or copper. A RTD consists of a length of fine wire wrapped around a ceramic or glass core. It has a slow response time but provides accurate values. Resistance thermometer, which also known as Resistance Temperature Detector (RTD), is a device used to measure temperature by changing its resistance depending on the surrounding temperature. These types differ in response speed, temperature ranges, accuracy, and other factors. There are many types of temperature sensors, such as LM35, thermistors, and resistance thermometers. Most of hardware developers have used a temperature sensor in one or more of theirs projects.
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