B - Temperature reading (18-05-18) Flashcards
What are the 2 types of temperature measuring?
Thermal expansion (bimetallic strip/direct reading thermometer/Gauge)
Electrical (remote reading temperature probe)
What is the principle of operation of thermal expansion temperature measuring?
2 metals of difference thermal expansion properties are bonded so that a temperature change will cause a deflection which can be measured for measure temperature.
The sensing element must be outside with the gauge inside.
What is the principle of operation of electrical temperature measuring?
Air flow is made to turn 90 degrees to remove moisture so that temperature is measured from dry air. This flow then flows past an electrical sensor.
The need for air flow means this doesn’t work well on the ground at low speeds so an aspirator is used to force flow to move. (Essentially a fan)
What is Static Air Temperature (SAT)?
Essentially outside air temperature
What is Total Air Temperature (TAT)?
A theoretical temperature of SAT plus ram rise
What is ram rise?
When air flow is slowed or stopped by a surface some of it’s kinetic energy is converted to heat.
This increase in temperature is ram rise.
What is Ram Air Temperature (RAT)?
A measured temperature of SAT plus ram rise.
What is Corrected OAT (COAT)?
IOAT corrected to be actual air temperature/SAT/OAT
What is Indicated OAT (IOAT)?
The temperature shown on the temperature gauge.
What is the recovery factor (KR)?
The extent to which RAT differs from TAT.
How can ram rise be determined?
On the CRP5 blue range using TAS.
Or
(TAS/100)2
What is the equation for calculating SAT from TAT, M and KR?
SAT = TAS/(1 + (0.2 x KR x M2))
What is a thermocouple and how can they be used?
Where 2 metals are joined together in a circuit and heating one of the junctions causes a current to flow. This current can be measured to determine the temperature change as long as one of the 2 junctions is kept at a constant known temperature.
What metals are used to measure temperature in the cylinder head of a piston engine and what is the maximum temperature?
+ve wire, iron
-ve wire 40% Nickle, 60% Chromium
Max temperature 850degC
What metals are used to measure temperature in the exhaust gas of a piston engine and what is the maximum temperature?
+ve wire, 90% Nickle, 10% Chromium
-ve wire, 90% Nickle, 2% Chromium and 8% trace metals
Max temperature 1100degC
