Resistance measurement three-wire bridge

For these thermometers, the electrical resistance of a metal or metal oxide changes with temperature. This resistance change can be measured by three-wire or four-wire null bridges (or Wheatstone... 

In most cases, three-wire RTDs are used in the industry, so these will be considered here. Mainly, bridge circuits using a modified Wheatstone bridge are used. In these circuits, measured output voltage is a function of the RTD resistance. Requirements for RTDs are similar to thermocouples. Use of a double-channel AC barrier with parameters discussed later will be a cost-effective solution. 

The thermal conductivity measurement of nanofluids was conducted with the fluid without any vibration. Each test was conducted at ambient condition, and the data were collected for 131 s. After repeated trials it was found that the variable resistor should be balanced slightly above the known resistance of the platinum wire. Once the bridge is properly balanced, the variation of voltage with time was measured and recorded. The measured thermal conductivity data was calibrated using three kinds of fluids. 

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