Electronic Components. Electronics. Resistors and Basic Circuit Laws. Basic Circuits. Basic Circuit. Voltage Dividers

Transcription

1 Electronics most instruments work on either analog or digital signals we will discuss circuit basics parallel and series circuits voltage dividers filters high-pass, low-pass, band-pass filters the main purpose of this chapter is to get you to understand the electronic filters they help to reduce electronic noise less noise a clearer signal (more on this in Chapt 5) Electronic Components esistors: resists the flow of electron through a circuit units of Ohms (Ω) with symbol Capacitors: resists changes in the voltage of a circuit (capacitive reactance) units of Faradays (usually μf or nf) with symbol O Inductors: resists changes in the current of a circuit (inductive reactance) units of Henry s (H) with symbol esistors and Basic Circuit Laws a few Laws to provide equations (V voltage, I current, resistance) Ohm s Law: VI Power Law: P IV O P V / Basic Circuits series batteries voltage adds to produce a higher voltage Kirchoff s Laws current law: the algebraic sum of the current around any point in a circuit is zero voltage law: the algebraic sum of the voltages around a closed electrical loop is zero parallel batteries currents add to add a higher current capacity Basic Circuit series resistors resistance add directly T same current through each parallel resistors resistance add as reciprocals 1/ T 1/ 1 + 1/ +... same voltage drop across each since the same current goes through each resistor, there is different voltage drop across each the total voltage divides across the series Voltage Dividers 1

2 Example : a Voltage Divider calc. T calc. each V T T T 450 Ω 150. Ω Ω Example : a Voltage Divider calc. T calc. each V V I T T or I T V/ T I T 100. V/450. Ω I T 0. A 150. Ω Ω T 450. Ω Example : a Voltage Divider V 1 I T 1 V 1 (0. A)(50. Ω) V V 11 V V I T V (0. A)(150. Ω) V 33.3 V 150. Ω Ω T 450. Ω I T 0. A Current Dividers since the voltage is the same across each resistor, the current across each is different the total current is divide across each parallel path scan fig -3 on page 4 V 3 I T 3 V 3 (0. A)(50. Ω) V V Example : a Current Divider Example : a Current Divider 150. Ω Ω calc. each I 150. Ω Ω I 1 V/ V/50. Ω.0 A I V/ 100.V/150. Ω0.667 A I 3 V/ V/50. Ω0.400 A

3 Example : a Current Divider Loading Error making a measurement causes an uncertainty in the measurement (analogous to the Heisenburg Uncertainty Principle) E r V M V V x x 100% 150. Ω Ω I T I 1 + I + I A I T A 3.1 A E r S + M S 100% Loading Error AC Circuits 0-10 % Error Chopping (AAS) , ,000 10,000,000 M (Ω) The error drops as the internal resistance of the meter increases electrochemistry electrochemistry Inductors/Capacitors Capacitors: resists changes in the voltage of a circuit (capacitive reactance) units of Faradays (usually μf or nf) with symbol O Inductors: resists changes in the current of a circuit (inductive reactance) units of Henry s (H) with symbol AC signals are constantly changing, so including these components in the circuit affects the signal C Calculations reactance: the capacitor's equivalent to resistance there is a frequency dependence 1 1 X C πfc ωc impedance: the total resistance in an C circuit there is a frequency dependence Z + X C + πfc 3

4 X C VC V Z V since this circuit is a voltage divider the voltage across the resistor is V V V V T Z + πf the voltage across the capacitor is πf + πf as f, V? as f, V C? as f, V? as f, V C? At high freq. the capacitor becomes practically a wire its reactance goes down and no voltage is dropped across it Voltage (% of input) 100% 75% 50% 5% 0% V VC ,000 10,000 Signal Frequency (Hz) C Circuit Distortion Distortion is dependent on the size of C See homework problems C Circuits the capacitor cause a time lag in the voltage (phase shift) dv i C dt φ arc tan πf C Circuits the phase shift is frequency dependent, decreasing as the frequency increases Phase Shift (degrees) φ arc tan πf 1 kω C 1 nf ,000 1,000, ,000,000 Signal Frequency (Hz) 4

5 Electronics Definitions resistance how a resistor effects a circuit reactance how a capacitor or inductor effects a circuit impedance the combination of resistance and reactance Other Components diode allows current to flow in only one direction; used in regulators transitors can act as an amplifier or switch replaced the vacuum tube transformer converts one AC voltage to others rectifier & filter converts AC to DC regulator prevents surges in current from changing the voltage of a power supply oscilloscope a device to read and analyze signal and circuits 5