1. Analog Circuits Seth Price Department of Chemical Engineering New Mexico Tech Rev. 8/31/14

2. Ohm’s Law E = IR – E is the voltage across a component – I is the current through a component – R is the resistance of the component

3. Common Schematic Symbols

4. Resistors All components have some resistance Convert current into heat: P = I 2 R Have a maximum power rating Color coded for value

5. Resistor Color Code

6. Series/ Parallel Combinations Series: the same current passed through multiple components Req = R1 + R2 + … Parallel: the same voltage is across multiple components 1/Req = 1/R1 + 1/R2 + ….

7. Kirchoff’s Current Law (KCL) Any current flowing into a node must also leave the node: – The sum of all currents at any point = 0

8. Kirchoff’s Voltage Law (KVL) The sum of the voltages around any closed loop must equal zero – Any voltage generated must be dissipated

9. Using a Multimeter Measure voltage in parallel – Meter is used to measure voltage ACROSS a device, or with respect to ground – Meter tries to have infinite impedance (resistance) Measure current in series – Must break circuit and put meter IN loop – Meter tries to have no impedance

10. 3-Point Safety Check To check to see if an industrial circuit is live: – Measure known voltage (ex: wall outlet) – Measure voltage on what you think has no power – Measure known voltage again WHY? – If your multimeter lead is loose, it will display “0” – If you have a blown fuse, it might display “0” – Maybe the circuit is still live!!!

11. Current Limiter Used to protect devices by lowering total current A resistor in series drops current in loop http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/

12. Shunt Resistor High currents are hard to measure Instead, place a small resistance (of known value) in series Measure voltage drop across resistor From Ohm’s law: I= V/R http://www.reuk.co.uk/What-is-a-Shunt.htm

13. Wheatstone Bridge Easy to detect small voltages R1, R2 and R3 are known Rx is adjustable – Perhaps a sensor As Rx changes, the currents changes, Vg changes http://en.wikipedia.org/wiki/Wheatstone_bridge