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Mission Statement 

The purpose of FLAPS-2-APPROACH is two-fold:  To document the construction of a Boeing 737 flight simulator, and to act as a platform to share aviation-related articles pertaining to the Boeing 737; thereby, providing a source of inspiration and reference to like-minded individuals.

I am not a professional journalist.  Writing for a cross section of readers from differing cultures and languages with varying degrees of technical ability, can at times be challenging. I hope there are not too many spelling and grammatical mistakes.

 

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I use the words 'modules & panels' and 'CDU & FMC' interchangeably.  The definition of the acronym 'OEM' is Original Equipment Manufacturer (aka real aicraft part).

 

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Journal Archive (Newest First)
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Sunday
Jul212013

Flight Deck Builders Toolbox - Multimeter

Depending upon how much realism you’re seeking, the construction of a flight simulator can encompass a variety of techniques including: electrical, mechanical, metal and wood-working, computer and IT skills. 

The average person, unless gifted or working in these fields, rarely has the level of expertise needed to fulfill every facet of building.  Fortunately, there are others that have travelled along the same path and assistance is often relatively easy to find from the Internet and dedicated builder forums.

LEFT:  Multimeter by Fluke (click image for larger view).

One skill I was lacking was electrical.  As a youngster I had dabbled with car radios, stereos and installed numerous two way radios into cars and boats.  I can remember sparks flying here and there as I connected wires incorrectly.  The only gadget I owned then was a retro-looking screwdriver that had a handle that illuminated whenever a live wire was touched.

Although many builders opt for pre made parts that do not require wiring and soldering, there will come a time when you have to do this yourself, especially if you are using real aviation parts converted to flight simulator.

The Multimeter

A multimeter is used for diagnosing problems with electrical systems and is probably the most useful tool any builder can have in his arsenal of tools.   If I’d had access to a multimeter in my earlier years, I’m sure the sparks would not have been as bright as they were and I wouldn’t have “fried” some many fuses and radio components.

Most multimeters can be used to measure a number of variables, the most valuable in my opinion being the ability to measure of continuity.

Continuity Testing - numerous examples

One of the basic uses a multimeter has in flight deck building is to test for continuity.  Testing for continuity checks to see if there is an electrical connection between two points. If two points are electrically connected, they are said to be continuous and the current will flow unheeded.  

Testing for continuity has many useful purposes.

For example, you can determine which prong on a multi-prong Canon plug is being used to carry 5 Volts to power the back lighting on a real aviation gauge or panel.  Another example is checking to ensure current flow across wires from an interface card to a sim part.  

A further example is aircraft bulbs.  Often they are so small that viewing the filament to determine connectivity is next to impossible.  Grab your meter and place a probe on the outside of the bulb (the earth) and place the other probe at the power end of the bulb (positive).  If you hear the meter beep then the filament is not damaged and current can flow, however, if you don’t hear the beep, then the current is not flowing and the filament is damaged requiring a replacement bulb.  A similar test can be done with fuses.

Continuity testing can also help you test your soldered connections to see if they were soldered correctly.  A beginner who is not experienced in visually detecting problems with a soldered joint can become frustrated very easily, because a soldered joint can look like its soldered correctly but there may not be an electrical connection. Using a mulitmeter helps you find out if the soldered connection is good or not.  Similarly, the tool can also be used to determine if a correctly connected wire is broken somewhere along the wire’s strand.

How to Test for Continuity

Set your multimeter to the correct mode.  Look for the icon that looks like a sound wave or a Wi-Fi connection indicator on the meter.  If you can't find it refer to the manual you received with the multimeter.

  • Using the pencil probe (red or black wire), touch the connection you want to test.  
  • Using the other probe, touch the other end of the connection you want to test.
  • If you hear a beep or a buzz, there is an electric connection between the two points. 
  • If there is no electrical connection you will not hear a beep or a buzz and the display will give a reading of 0.

Example - Connecting Back Lighting

 Using continuity, let’s look at the example mentioned earlier: connecting power to illuminate back lighting on an OEM gauge that uses a multi-prong canon plug.   

We need to determine which of the prongs from the plug carries power (positive) and which is earth.  

LEFT:  Note the black probe is touching the outer casing (earth) whilst the red probe is being moved from prong to prong.  An audible beep from the multimeter will sound when the prong touches the power prong.  It's important to ensure you are only touching one prong at a time, otherwise you will get an erroneous result (click image for larger view).

  1. To check for power, touch one of the two probes to one of the prongs in the Canon plug.  Then, attach the other probe to the lower positive end of the bulb (not the bulb casing).  Move the first probe from prong to prong in the Canon plug until you here a beep.  The beep indicates that this prong is the power prong. 
  2. To determine earth, do the same technique, but instead of using the bulb, touch the probe against the outer casing of the Canon plug.  With the other probe move it between each of the prongs in the plug.  When you hear the beep this will indicate which prong is earth.   
  3. The wires from the power supply (positive and earth) are then connected to the indicated prongs.  The back lighting of the gauge will illuminate.

The same can be done for switches and toggles or for almost any part.  Let's look at another example:   

Example - Connecting a Switch or Toggle

In this case we have a three-was switch often used in the overhead.  The switch can be moved to three positions and can be locked in one position.  The rear of the switch has three terminals.  before going further, it's important to realize that although a switch may have up to eight terminals, not every terminal is needed to connect to the simulator.  The reason there are often ancillary terminals is that in the real aircraft, a switch may also connect to other devices that a simulator does not need (such a centralized computer).

To determine which switch position correlates to the actual turning on or off of the function we need to:

  1.  Place the black probe on the earth or common terminal.
  2. Place the red probe on another terminal (alligator clips are handy you secure the probe to the terminal).
  3. Move the switch toggle up and down until you hear the multimeter beep.  The beep signifies that power can travel through the circuit.
  4. Remember the position of the switch and the terminal used.
  5.  Repeat the process with all terminals and double check results to ensure accuracy.
  6. Once the terminals (or pin outs are known) connect the appripate wires from the interface card and program in the flight avionics software to that that functionality.

Other Functions and Uses

Testing for continuity is but one operation of a mulitmeter, and depending upon the type and quality of the tool, there will be other functions available, such as being able to measure current, resistance and voltage.  The last function is very handy to flight deck builders as often we use multiple voltages ranging from 3, 5, 12 and 28 Volts.  By turning the dial to the appropriate voltage selection, one probe is used to touch one side of the wire and the other probe the device.  This will determine what voltage current is travelling through the wire to/from an interface card.

Measuring current can be equally important, and to determine current flow between points, the probes are connected to each side of the device to be measured.  With the probes effectively interrupting the current flow, the meter is “in-line” and any current travelling between the components will be able to be measured and displayed by the meter in amps.  

There you have it, the very basics of a multimeter and why it’s important to have one in your toolbox.

Thankfully, I’ve not had any sparks or melted wires building the simulator and it’s primarily because I always use a multimeter to check any work I’ve done before turning the power on.  

I still have the retro flashing screwdriver, but it’s more a keepsake than an operational tool.

To read a sister post, navigate to: Using Interface Cards and Canon Plugs to Convert OEM B737 Parts.

Below is a video courtesy of Afrotechmods (U-Tube creative commons license) which explains how to use a multimeter.

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Reader Comments (5)

Thank you very much for this highly educational article,
I am following your blog closely for some time now and appreciate the broad range of sim-related topics you cover.
Keep up your outstanding effort!

Greetings from Hamburg, Germany!

July 22, 2013 | Unregistered Commenterflaremaster

Nice introduction to electronics.

There's a small typo.Ohms is resistance not current. Current is measured in amps (or usually milliamps).

July 22, 2013 | Unregistered CommenterNed Hamilton

As always Ned, I appreciate your input...

Thank you @FlareMaster. I appreciate your kind words and I'm very pleased you enjoy the Blog. Cheers F2A

July 23, 2013 | Registered CommenterFLAPS 2 APPROACH

This is a highly detailed guide and a very useful introduction to electronics. I will keep an eye on your blog to, keep up the good work.

September 20, 2013 | Unregistered CommenterDavid

Fluke does make the best multimeters and this is a great example of one of them.

November 10, 2013 | Unregistered CommenterSteven Larson
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