## Basic Electricity

### How Juiced Are You?

I never understood electrical technicians. Why they liked to play around with something as hazardous as electricity is beyond me. Sometimes I think they were those young toddlers we always hear of sticking the family silverware into the electrical socket just to see how straight up they could make their hair stand. Heck of a way to measure current or voltage, but I guess somebody has got to do it and they feel it has to be them. “Hmm…hair is only standing up about 90% and the convulsions are not as severe as last time…there must be a higher load on the electrical system right now…I bet it’s Mom using the washer to wash my diapers again.”

Thankfully, there has been progress made for people who like to stick pointy metal objects into sockets, probably demanded by their horrified mothers. Electrical technicians eventually gave up the silverware for other unique measuring devices that turned out to be a whole lot safer but a bit more cumbersome. Meters were created that measured many properties of electricity. There were meters for Volts, Current, and Ohms (resistance) that required the technician to carry as many as three heavy analog meters to their jobs. Eventually, someone came up with a meter that could measure all three properties. “The invention of the first multimeter is attributed to British Post Office engineer, Donald Macadie, who became dissatisfied with having to carry many separate instruments required for the maintenance of the telecommunications circuits.”

“Multi” means “multiple” and “meter” means “to measure.” The first multimeters were analog. Some were large machines that were made to sit on an electrical technician’s bench and could do detailed measurements while running off AC power. Others were smaller and used to do troubleshooting in the field. These ones ran on a battery and could be held in your hand. Both types had a needle type gauge that would move and give you the reading you were testing for. Eventually, most multimeters went digital and gave you a numeric value on a screen.

A typical multimeter will have at least four sections:

- Display screen
- Function switch
- Range selector
- Input jacks and test leads

Displays are pretty much self explanatory. It displays the value of what your measuring. If you are measuring volts, the display will show you the volts measured.

The function switch allows you set the multimeter to the property you are measuring. If you wish to measure AC volts, you would move the selector to ACV for example.

The range selector allows you to narrow down the range of what your measuring so you can get a more accurate reading. For example, if you are measuring direct current volts, and you are not sure what range to select, you would first select the maximum value of 1000. If the display reads much lower than 1000, then you can “dial down” the selector to a value just above what the volts are. This way you get a more accurate reading.

And of course, you can’t measure anything without having probes and the input jacks for them. This is where the electrical technicians get to relive their childhood experiences. You plug into the proper input jack (see your owner’s manual for which one) and you get to stick the probe into something electrical. At least your mother is not standing over you freaking out while the house lights dim again.

Seriously, as for any device, read the owner’s manual for further instructions and have a expert teach you about that particular multimeter. And please, resist the urge to stick your silverware into any sockets. Your too old now and your heart just can’t take it anymore!

Other Sources:

Nida Series 130E Lab/Text Manual April 2002

http://zone.ni.com/devzone/cda/tut/p/id/3295

http://www.kpsec.freeuk.com/multimtr.htm#diode

### Magic Triangles

Electronics is a major part of some aerospace technician’s workday. As an aerospace technician, it is considered a basic skill to be able to calculate voltage, current (amps), power (watts), and resistance (ohms), but remembering the formulas that go into those calculations can be difficult. This is where a “magic triangle” can help.

The first thing you need to remember is the correct formula sign. What letter or symbol represents each of these values. The table below should help and can be cut out and kept in your badge holder if you want.

Name |
Formula sign |
Unit |
Symbol |

voltage |
V or E |
volt | V |

current |
I |
ampere (amp) | A |

resistance |
R |
ohm | Ω |

power |
P |
watt | W |

To calculate power (watts), voltage, and current you can try to memorize three different formulas depending on which value your looking for or you can use a Power Triangle.

To find the value your looking for, just cover up the formula sign on the triangle and do the calculation you see. Let’s say you have measured the volts and current with your multimeter, you can cover the P up on the triangle with your thumb and see that you need to multiply volts by current to get the wattage (power) that is being passed over the line. Or, say you want to find out the volts and all you can measure is the watts (P) and current (I). You cover up the V on the triangle and discover you need to divide P by I to get the answer. It’s really not that difficult using the Power Triangle and sure beats trying to remember three separate formulas.

To calculate resistance using the Ohms law, there is another magic triangle called the Ohms Law Triangle. This triangle will help you calculate resistance, current (I), and voltage. This can also help you figure out how large of a resistor you want to place in a circut to obtain a specified current and voltage.

To calculate what type of resistor you need to obtain the proper resistance in a circuit, you would cover the R on the triangle and see that you need to divide Volts by Current. If you already have a resistor on the circuit and wish to know the current, you can divide volts by the resistance to get the answer after you cover up the R on the triangle. Not too hard is it?

For more advanced calculations, you might also find this Power Wheel handy.

Overall, power calculations don’t have to keep you up at night or calling your former electronics instructor right in the middle of a job. All it takes is just a couple “magic triangles” to help you through.