I am testing a gas turbine engine (RC) as a part of my university experiment, and I am confused with the usage of the sensors. What type of sensor do I need to use? Differential or the pressure, absolute or gauge?
I see you're a student; that's good. And you want to test a gas turbine; that's good, too.
What is the purpose of your test? Are you testing the thrust developed by the turbine? Are you testing the efficiency of the turbine (fuel per unit thrust)? Are you testing the mass flow through the turbine (inlet and/or exhaust)?
Gas turbines generally suck, squeeze, burn and blow. That means they draw air into the axial compressor, the axial compressor increases the pressure of the air, they burn fuel in a combustor (or combustors) with the compressed air, and they exhaust to a turbine to drive the axial compressor and produce some useful work (torque; thrust). There are MANY variables which can be monitored for one purpose or another, and the choice of sensor will depend on what is being measured, and it's not just pressure, it's also temperature.
So, first you have to define what is being tested, and then you can choose the type of sensor(s) (many tests involve more than one sensor, and more than one type of sensor) and the engineering units which will be used by the sensors.
For example, to measure efficiency one has to measure the amount of fuel being consumed which can use a flow-meter (for liquid fuel), or a differential pressure measuring arrangement across an orifice of known size (for gas fuel). There are also other types of flow measurement sensors--it all depends on the accuracy you require, and--of course!--the cost of the sensors, as well as any associated equipment to record the outputs of the sensors for analysis. One also has to measure the work being produced by the turbine (thrust; torque; electric power output of a generator if the gas turbine is driving an electric generator; and so on).
It's really impossible for anyone to say use this or that sensor with these or those engineering units unless the intent of the test is known.
As a student of gas turbines, you need to be aware of how the gas turbine operates (suck; squeeze; burn; blow) and all of the parameters which are monitored for control and protection of the turbine and its auxiliaries, too. And, this will guide you selection of instruments for the gathering of the data for the type of test you will be performing.
Hope this helps!