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STEADY STATE PROPERTIES OF TEMPERATURE SENSORS 1. task RESISTIVE TEMPERATURE DETECTOR Pt 100 Tasks of measurement: 1. Measure static characteristic Rt = f(temperature) of resistive sensor Pt 100 in temperature range from 30 °C to 80°C. Make measurements by Data Acquisition Control Unit Agillent and by hand balancing a DC bridge. 2. Draw the measured characteristic and compare the measured data with a reference value from Pt100 calibration table according to DIN IEC 751. 3. Determine sensitivity of sensor (/°C) for 40°C and for 80°C. Table of measured values: t (°C) Rt () Agilent Rt () hand balanced Rt () DIN IEC 751 30 40 50 60 70 80 Wiring diagram: Measuring instruments: Data Acquisition Control Unit Agillent Thermowell with resistive temperature detector Pt 100 Note: Make all characteristics in this lab together by warming the water in a thermo controller. Steady state has to be reached before every reading. Schematic of a hand balanced DC bridge Three wire connection This is a most common connection. As the bridge is initially balanced and resistance changes of connection wires is connected to both bridge diagonals, the eventual change of connection wire resistance with temperature is compensated (provided that all wires are heated equally). In this every connection it is necessary to carefully choose the power supply voltage in order to limit the current going through the temperature sensor. Set the current with the variable resistor on the fixture to 2 mA. As we are measuring the total bridge current, when the bridge is balanced, the Pt100 current is the half of the total current, ie. 1 mA. Calculate sensor self heating, as P = R.I2 2. task THERMISTOR SENSOR Tasks of measurement: 1. Measure static characteristic R = f(temperature) of bead and disc thermistor sensors in temperature range 30°C to 80°C. Make measurements by Data Acquisition Control Unit Agillent and manually by a ohm meter. 2. Draw the measured characteristic for manual and automatic measurement. 3. Determine sensitivity of sensor (/°C) for 40°C and for 80°C Table of measured values: t (°C) Rt (k) bead therm. Rt (k) disc. therm. 30 40 50 60 70 80 Wiring diagram: Measuring instruments: Data Acquisition Control Unit Agillent Ohmmeter Thermistor sensor with bead thermistor Thermistor sensor with disc thermistor Note: Make all characteristics in this lab together by warming the water in a thermo controller. Steady state has to be reached before every reading. 3. task RESISTIVE SENSOR KTY 81 Tasks of measurement: 1. Measure static characteristic R = f(temperature) of resistive sensor KTY 81 in temperature range 30°C to 80°C. Make measurements by Data Acquisition Control Unit Agillent and manually by a ohm meter. 2. Draw the measured characteristic for both measurements and compare the measured data with a reference value from calibration table. 3. Determine sensitivity of sensor (/°C) for 40°C and for 80°C Table of measured values: t (°C) 30 Rt () Agillent Rt () ohm meter Rt () calibration table 40 50 60 70 80 Wiring diagram: Measuring instruments: Data Acquisition Control Unit Agillent Ohmmeter Semiconductive resistive temperature sensor KTY 81 Note: Make all characteristics in this lab together by warming the water in a thermo controller. Steady state has to be reached before every reading. 4. task THERMOCOUPLE TYPE J Tasks of measurement: 1. Measure static characteristic Ut = f(temperature) of thermocouple type J in temperature range 30°C to 80°C. Make measurements by Data Acquisition Control Unit Agillent. 2. Draw the measured characteristic and compare the measured data with a reference value from thermocouple type J calibration table. 3. Determine sensitivity of sensor (/°C) for 40°C and for 80°C Table of measured values: t (°C) 30 40 Ut (mV) Ut (mV) calibration table Cold junction temperature (°C): Wiring diagram: Measurement instruments: Data Acquisition Control Unit Agillent Thermocouple type J 50 60 70 80 Thermal conductivity Tasks: 1) measure thermal conductivity [Wm-1K-1] of Plexiglas. 2) compare calculated thermal conductivity of Plexiglas with table value ( = 0,2 [Wm-1K-1]) and discuss eventual differences and sources of errors Thermal conductivity is the property of a material describing its ability to conduct heat. We will measure in a insulated box (insulated with Polystyrene, thermal conductivity = 0,039 [Wm-1K-1] ). Inside this box a heater (resistor R = 10 ) is heated with known current. Therefore we know that the input power is P = R. I2 .Two temperatures are measured, internal surface temperature ti and external surface temperature te of the Plexiglas. Thermal conductivity can be calculated from equation (1): P·d A·t [Wm-1K-1] (1) where P is input power [W], d = 0,003 is Plexiglas thickness [m], A is area of the Plexiglas window where the heat can go out of the box (10 x 10 cm) and t = ti - te is temperature difference between the temperature of internal and external surfaces. !!!Remember: It is necessary to measure in STEADY STATE, therefore wait until both temperatures are steady !!! Table of measured and calculated values I [A] P[W] d [m] A [m2] R [] 0,7 10 Used equations P R·I 2 [W] P·d A·t Conclusions [Wm-1K-1] ti [°C] te [°C] [Wm-1K-1]