1 / 21

Lecture 6

Lecture 6. Review: Circuit reduction Circuit reduction examples Practical application Temperature measurement Related educational modules: Section 1.5, Lab assignment 2. Review: series resistors and voltage division. Equivalent resistance: Voltage divider formula:.

beverlymartin
Télécharger la présentation

Lecture 6

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 6 Review: Circuit reduction Circuit reduction examples Practical application Temperature measurement Related educational modules: Section 1.5, Lab assignment 2

  2. Review: series resistors and voltage division • Equivalent resistance: Voltage divider formula:

  3. Review: parallel resistance and current division • Equivalent resistance: Current divider formula:

  4. Checking parallel resistance results • The equivalent resistance of a parallel combination of resistors is less than the smallest resistance in the combination • Resistance decreases as resistors are added in parallel • Range of equivalent resistance: • Rmin is the lowest resistance; N is the number of resistors

  5. Examples: Non-ideal “loaded” power sources • Loaded voltage source: • Loaded current source:

  6. Circuit Reduction • Series and parallel combinations of circuit elements can be combined into a “equivalent” elements • The resulting simplified circuit can often be analyzed more easily than the original circuit

  7. Circuit reduction – example 1 • Determine the equivalent resistance of the circuit below

  8. Circuit reduction – example 2 • Determine Vout in the circuit below.

  9. Circuit reduction – example 3 • In the circuit below, find i1, VS, and VO.

  10. Example 3 – continued

  11. Example 3 – continued

  12. Circuit reduction – example 4 • In the circuit below, determine (a) the equivalent resistance seem by the source, (b) the currents i1 and i2

  13. Example 4 – continued

  14. Practical application – temperature measurement • Design a temperature measurement system whose output voltage increases as temperature increases • In general, we will typically have other design objectives • For example, power and sensitivity requirements • We neglect these for now; lab 2 will provide a more rigorous treatment of this problem

  15. Temperature sensors: thermistors • Thermistors are sensors whose resistance changes as a function of temperature • Thermistors are classified as either NTC (negative temperature coefficient) or PTC (positive temperature coefficient) • Resistance increases with temperature for PTCs; Resistance decreases with temperature for NTCs • A resistance variation is generally not directly useful; information is generally relayed with voltage • We need to convert the resistance change to a voltage change

  16. Example thermistor characteristics • NTC 10K @ 25C • Negative temperature coefficient thermistor with (nominal) resistance of 10k at 25C • Response:

  17. Initial Design Concept • Use voltage divider to convert resistance variation to voltage variation • Design problem: choose Vs and R to obtain desired variation in Vout for a given variation in temperature

  18. Potential Design Issues • Sensitivity • Our design requirements may specify a minimum voltage change per degree of temperature change (the sensitivity of the instrumentation system) • We can affect the sensitivity with our choice of R • Power requirements • We can increase the sensitivity by increasing VS • Increasing VS increases the power required by the system; increasing power (generally) increases cost • The above can cause us to modify or discard our initial design concept!

  19. Effect of resistance change on voltage

  20. Demo: • Change of thermistor resistance with temperature (DMM) • Change of output voltage from voltage divider • R<<RTH • R>>RTH • Intermediate R

More Related