Temperature Measurement Flashcards
How do you convert Kelvin to Celsius and vice versa?
K = C + 273.15 C = K - 273.15
What principle are thermocouples based upon?
Describe this effect.
Thermoelectric effect or Seebeck effect.
This effect describes how two different metals in contact generate a voltage, which is temperature dependant. There is a linear relationship between voltage and temperature.
How does a thermocouple work?
Makes use of a hot junction and a reference junction which is kept at a standard temperature that is colder than the hot junction. The voltage is effectively proportional to temperature measured.
What’s a thermopile?
When multiple thermocouples are combined in SERIES to increase the sensitivity of measurement, make a thermopile.
Not in parallel.
What are thermistors?
A type of resistor that has resistance that changes with temperature.
Allows them to accurately measure temperature to an order of 0.1 degrees C.
Made of semi conductor beads. Oxides including chromium, cobalt, iron and manganese may be used.
What is the negative temperature coefficient?
Present in a thermistor, this means that as the temperature rises the resistance of the thermistor falls. The relationship is non-linear.
However some thermistors can have a positive temperature coefficient.
What type of measurement devices are thermistors used in and why?
Suitable at end of pulmonary artery catheters and oesophageal temperature probes as they are accurate, small and cheap.
What are resistance thermometers?
Require a power supply and used more in industrial settings to measure very high temperatures. Not as accurate for small changes in temperature but have slower response time.
How do radiation thermometers work?
Convert infra-red radiation in the region of 0.72 - 1000 micom on the electromagnetic spectrum, to an electrical signal.
Used in handheld thermometers.
(The rate of radiation is proportional to temperature to the 4th power)
Is human core temperature accurate measured tympanically?
Yes
