1. EKT 314/4 WEEK 7 : CHAPTER 3 SIGNAL CONDITIONING ELECTRONIC INSTRUMENTATION

2. Chapter 3 Content Introduction Signal Conditioning Circuit (SCC) Function Preliminary Requirement Signal Conditioning (SC) System Type Amplifier Modulator Filter

3. A network designed to attenuate certain frequencies but pass others without attenuation is called a filter. Possess at least one pass band (band of frequencies in which the output is approximately equal to the input) and an attenuation band in which output is zero (attenuation is infinite). The frequencie(s) that separate the various pass and attenuation bands are called the cutoff frequencies.

4. Types of Filters Low pass High pass Band pass Band stop All pass

5. Ideal Response – Low Pass

6. Low Pass Filter

7. Ideal Response – High Pass

8. High Pass Filter

9. Ideal Response – Band Pass

10. Band Pass Filter

11. Ideal Response – Band Stop

12. Ideal Response – All Pass

13. Filter – Classifications Passive Filters Active Filters

14. Passive Filters A passive filter is a kind of electronic filter that is made only from passive elements. It does not require an external power source (beyond the signal). Since most filters are linear, in most cases, passive filters are composed of just the four basic linear elements – resistors, capacitors, inductors, and transformers. More complex passive filters may involve nonlinear elements, or more complex linear elements, such as transmission lines.

15. Passive Filter Advantages A passive filter has several advantages over an active filter: Guaranteed stability Passive filters scale better to large signals (tens of amperes, hundreds of volts), where active devices are often impractical No power consumption, but the desired signal is invariably attenuated. If no resistors are used, the amount of signal loss is directly related to the quality (and the price) of the components used. Inexpensive (unless large coils are required) For linear filters, generally, more linear than filters including active (and therefore non-linear) elements

16. Active Filters An active filter is a type of analog electronic filter, distinguished by the use of one or more active components i.e. voltage amplifiers or buffer amplifiers. Typically this will be a vacuum tube, or solid-state (transistor or operational amplifier).

17. Active Filter Advantages Inductors can be avoided. Passive filters without inductors cannot obtain a high Q (low damping), but with them are often large and expensive (at low frequencies), may have significant internal resistance, and may pick up surrounding electromagnetic signals. The shape of the response, the Q (Quality factor), and the tuned frequency can often be set easily by varying resistors, in some filters one parameter can be adjusted without affecting the others. Variable inductances for low frequency filters are not practical. The amplifier powering the filter can be used to buffer the filter from the electronic components it drives or is fed from, variations in which could otherwise significantly affect the shape of the frequency response.

18. EKT 314/4 WEEK 7 : CHAPTER 3 END ELECTRONIC INSTRUMENTATION