changes in different situations. The variables investigated were flow rate inside a submerged helical coil and agitation of the bath. To investigate the change in heat transfer coefficient in different situations, a simple experiment was set up. It consisted of a rectangular isolated tank, which was filled with water, submerged steel coil and an agitator. A rotameter was used to measure the flow rate, and a pump was used to force the water through the coil. A thermocouple was placed at each end of the coil to measure the inlet and outlet temperatures and another thermometer used to measure the overall temperature of the water inside the bath. Two different approaches were taken, one of them was investigating heat change coefficient in steady state and the other was studying it in an unsteady state. In steady state, a constant flow rate and agitation was applied until temperatures stayed constant, then were the readings taken
RTD resistance is specified at 0°C. A typical platinum RTD with 100 W resis- tance at 0°C would have a resistance of 100.39 W at 1°C and a resistance of 119.4 W at 50°C. The tolerance of RTDs is better than thermistors. Typical tol- erance for RTDs looks like this: Platinum: .01% to .03% Copper: .2% Nickel and nickel/iron: .5% Aside from better tolerance and overall lower resistance, the interface to an RTD is similar to that for a thermistor. Thermocouples A thermocouple is made by joining two dissimilar metals. Thomas Seebeck discovered in 1821 that when such a junction is heated, it generates a tiny voltage. The amount of voltage is dependent on which two metals are joined. Three common thermocouple combinations are Iron-Constantan (Type J), Copper-Constantan (Type T), and Chromel-Alumel (Type K). The voltage produced by a thermocouple junction is very small, typically only a few millivolts. A type K thermocouple changes only about 40 mv per °C
order to discharge any static built-up. Not doing so may result in malfunction or damage. • Do not touch the Expansion I/O Unit Connecting Cable while the power is be- ing supplied in order to prevent any malfunction due to static electricity. • When using a thermocouple-input type Temperature Sensor Unit, observe the following precautions: • Do not remove the cold junction compensator attached at the time of deliv- ery. If the cold junction compensator is removed the Unit will not be able to measure temperatures correctly. • Each of the input circuits is calibrated with the cold junction compensator
annaabi.ee 
