Download thermistor sensor

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]