EMT 478/3 Instrumentation Lecture 1 : Measurement Setup in electronic applications

1. EMT 478/3 InstrumentationLecture 1 : Measurement Setup in electronic applications • Objectives: • To realize the important of measurement setup in electronic applications • To develop understanding of measurement tools to obtain microwave frequencies • To get to know briefly on measurement of sensitivity and selectivity • The assignment is in the form of individual work on the topic of your Final Year Project (FYP) related to the measurement setup. Please refer to scientific journals (Nature, Science, Journal of Applied Physics, IEEE Transactions on Instrumentation and measurement,Review of Scientific  Instruments,IEEE Transactions on Biomedical Engineering,Journal of Scientific Instruments).

2. Introduction • Whatever the nature of applications, the measurement setup are based on a broad knowledge of what type of tools available, and how the performance of the tools to describe the best of the job to be done. • Nowadays, new devices is continuously being developed and invented therefore the measurement tools are seriously important in order to prove the usefulness of the devices in broad areas and undoubtedly will be used for many years. • In the other hand, the knowledge of general principles and techniques are needed in handling the measurement setup and also the type of the important parameter to be measured.

3. Amp Process Typical Measurement System Architecture Noise and Interference Signal Conditioner Process or Test Sensor or Transducer ADC Converter OUR TOPIC IS HERE PC comp and data storage Controller … and control over the process or experiment

4. Measurement of Microwave Frequencies • Measurement of microwave frequencies can be done by using a wavemeter. • The wavemeter is an adjustable resonant circuit completed with a calibration part gives the resonant frequency. • The wavemeter employs any type of resonant circuit that is compatible with the frequency to be covered. The examples of wavemeter are lumped constants, co-axial two lines and cavities. • The wavemeter may work in different way such as absorption, reaction and transmission. • In the absroption type, the wavemeter is equipped with means for indicating the current induced in it. • In the reaction type, the frequency is determined from reaction produced by the wavemeter upon the system being measured.

5. In the transmission type, the wavemeter is used as a coupling device in a system transmits power from a generator to a load.

6. Wavemeter: To measure microwave frequency • Resonant co-axial line • A resonant system that can measure frequency between 600 to 10,000 MHz • At lower frequencies, the cavity becomes excessively long and at the higher frequencies the dimension becomes small. • It has two coupling loops, one for feeding power into the line through a co-axial cable and another one for coupling a crystal rectifier indicator to the oscillators in the cavity. • The tuning process can be accomplished by varying the position of the short circuit plunger by using a lead screw. • The accuracy of the co-axial wavemeters could be quite high at value of 0.05%.

7. Cavity wavemeters • Same as co-axial lines type, the cavity wavemeters is used to measure microwave frequencies. • The advantages of the cavity wavemeters are high accuracy, mechanical simplicity and has large physical size in proportion to the wavelength to be measured. • The resonant frequency of the cavity is varied by means of a plunger, which is mechanically connected to a micrometer mechanism. Movement of the plunger into the cavity reduces the cavity size and increases the resonant frequency. Conversely, an increase in the size of the cavity (made by withdrawing the plunger) lowers the resonant frequency. The microwave energy from the equipment being tested is fed into the wavemeter through one of two inputs, A or B. The crystal rectifier then detects (rectifies) the signal. The rectified current is indicated on current meter M.

8. Cavity wavemeter

9. Strength meter: To measure the strength of the radio waves • Two general methods available for determination of field strength. • Using standard antenna method, the field strength is determined by measuring the voltage induced in the antenna and make use the relationship between it and the field strength. • The second method is known as the standard field generator method or the substitution method. It compares the strength of the radio waves with a field of known strength. It is intended for use at very high frequencies.

10. In the substitution method, the input of coaxial line can be switched from the receiving antenna to a signal generator, then the signal is adjusted to deliver the same power to the radio wave of unknown field strength.

11. Measurement of Sensitivity • The sensitivity of a radio receiver is its ability to amplify a weak signal. • It is often defined in the form of voltage that must be applied to the receiver input terminals to give a standard output power. • The formula of sensitivity can be extracted from the instrument response (based on the assumption that the response is linear). If input quantity changes by D QINP, resulting in the output quantity change of D QOUT, then the sensitivity is

12. Input-Output Response Curve for an instrument

13. Measurement of Selectivity • The selectivity of a radio receiver is described as the ability to only received the radio stations that the radio is tuned into while rejecting (adjacent) unwanted signals. • The ratio of a nearby stations frequency to the frequency that the radio is tuned into the receiver. • There is a wide variety of different types of RF filter used in radio receiver to provide the required selectivity such as LC filter, crystal filter, monolithic crystal filter, ceramic filter and mechanical filter.