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May 042014
 
This Avometer advertisement appeared in 1953, and offers the meter for £23.50, twice the average weekly wage at the time.  Similar meters today can cost only $23, closer to the average hourly rate.

This Avometer advertisement appeared in 1953, and offers the meter for £23.50, twice the average weekly wage at the time. Similar meters today can cost only $23, closer to the average hourly rate.

As we imagine and plan for a difficult life in the future, we realize that we will need to learn more skills than we currently have, because when things go wrong, we can’t simply go out and buy a replacement, and might not be able to find anyone conveniently nearby to fix the problem, either.

Hopefully you’ll continue to have at least some electricity at your retreat, and will be able to enjoy the extraordinary benefits that electricity has given to us all.  If you want to get a taste for just how extraordinary, beneficial, and essential those benefits are, treat yourself to a weekend with no electricity.  Turn off the main breaker in your fuse box on Friday night, and don’t cheat by using any batteries.  Go totally electricity-less for a weekend, and do it not when the weather is comfortable outside, but when it is either impossibly hot or impossibly cold.

Okay, now that you’re back reading the article again, and fully convinced about the essential role electricity has in your life (how long did you last before turning the breaker back on?) there’s every chance that at some future point, you’re going to have to become an amateur electrician, and maybe even an amateur electronics repair tech too.

You’ll not be able to repair anything if you can’t first troubleshoot to find out the problem.  Ideally, you’ll also want to be able to test the repair before making the fixed device ‘live’ once more, too.  Now the good news, particularly with electrical (as opposed to electronic) devices, is that many problems can be troubleshooted using that most sophisticated of instruments, the Mark I Human Eyeball.  You’ll spot breaks in cords, blown fuses, burned out plugs, and so on, just by looking.

But whether it is for troubleshooting, or for checking the correctness of repairs before plugging the devices back into your main power circuits, you’ll find everything you do will be immeasurably assisted by what is termed a ‘multi-meter’ – a device that will show you various things about electrical circuits – in particular, both amps and volts for AC and DC circuits, and also ohms for resistance, and with multiple scales ranging from fractions of a volt/amp/ohm up to tens of amps, probably thousands of volts and millions of ohms.

The first ever multimeters came out in 1923, and were the result of a British Post Office technician getting exasperated at having to carry so many individual test meters with him (and back then they were all big, bulky, and heavy, too).  His creation was the Avometer (Avo being an acronym for Amps, Volts, Ohms), and when first released it had seven different functions (three DC voltage ranges, three DC amperage ranges, and one resistance range).  When the Avometer finally and sadly ended production in 2008, it had 28 ranges, also now including AC volts and amps.

In the past, Avometers often cost more than a couple of weeks wages for the technicians using them, so they were hardly a commonplace device that people would have ‘just in case’ they might need it in the future.  But in time, more manufacturers started making similar devices, and with less robust but more automated manufacturing methods and standards, and so prices dropped amazingly.  I remember buying one as a teenager, very many decades ago, and at the time never gave thought to how such devices once cost hundreds of times more than they did then – and today, they are even cheaper still.  You can buy a reasonably multimeter from somewhere like Harbor Freight, or on Amazon or eBay, for under $20, and an excellent one for under $40.  So there’s no reason why you shouldn’t have one.

What To Look For When Choosing a Multimeter

A typical multimeter will be able to test at least five different things – DC and AC volts, DC and AC current, and resistances.  There are differences between meters, however, in terms of the minimum and maximum values it can read for all five of these scales.

Needless to say, you’d like a meter that has the broadest range of scales, but in terms of what you really need, if you are using your meter mainly for testing electrical devices, you probably need to be able to read DC volts from a minimum of maybe one or two volts (ie perhaps a 10V scale) up to a maximum of less than 1000V; DC amps from perhaps a 1A or 0.1A (100 milliamp) scale up to maybe 10A; AC volts from perhaps a 10V up to a 1000V scale; AC amps from perhaps a 1A scale and up as high as possible; and resistances from as sensitive a scale as possible (maybe a max of 10 kOhm on the scale, and showing individual ohms at the low-end of the logarithmic scale) up to showing maybe a 10 MOhm maximum scale).

If you will be using your meter for electronic troubleshooting as well as electrical troubleshooting, you might want to have some additional scales to show lower values for DC volts and DC amps, and probably a lower AC amp scale too.  You might also want to be able to read higher current flows too – this will likely require a specialized device (see below).

If you need other ranges beyond these, you’ll probably know about your special needs already.

A nice feature is a continuity buzzer.  This is useful when you’re doing mundane tasks like checking to see which ends of which wires relate to the other end of the same wires, or checking for breaks in circuits.  Instead of having to watch your meter, you simply touch your probes to things and if there’s a clear connection between the two things you are touching, the meter will buzz or beep.

It helps to understand, for the AC measurements in any meter, what range of frequencies the AC measurements are accurate for, and what types of waveforms it will accurately read.  If you’re just reading mains power type frequencies, then most meters will work well for that, but if you have unusual wave shapes or are wanting to measure audio or radio frequencies as well as mains frequency, then you will need a specialized meter that measures true RMS and higher frequencies.

Some meters have additional functions, including the ability to measure frequency, capacitance, inductance, temperature, diodes and some functions of transistors.  You’ll of course pay extra for such extra features, but if they have value to you, then why not get the ability, particularly because these extra functions don’t necessarily add much more to the price of the meter.

See further discussion in the section on analog or digital meters, particularly for some features that are unique to digital meters.

A meter should have at least one fuse in it to protect its circuitry from overload.  This is particularly essential in analog meters, where the meter’s integrity relies on you, the user, selecting the correct scale to start with whenever you connect the meter to anything.  Old hands know the rule ‘always start with the highest value range setting, and then switch down as needed’ from bitter experience.

Our point here is to identify the type of fuse used and to lay in a small supply of spares.  In the worst case scenario, if you blow the fuse, you can replace the fuse with regular wire or any other sort of fuse as well – the meter will continue to work, but it will no longer be protected, so your next mistake will probably fry it.  We’ve only once ever blown a fuse, so you probably don’t need to have too huge a supply of spares.

Accuracy Issues

Different meters make different claims about their accuracy, and some digital meters display more digits than others – indeed, they’ll probably display a more detailed number than their underlying accuracy allows.  By this we mean a meter that has an accuracy of +/- 3% might have a three or more digit display, so it could in theory show, say, 97.2 volts, whereas the actual voltage could be anywhere from 94.3V up to 100.1V – so what is the sense in telling you about the 0.2V when even the 7 volt part of the reading can vary widely from 4 up to 10.

Don’t get too hung up on accuracy issues.  Most of the time, the required value and tolerance of anything in typical electrical (and electronic) circuits is fine if it is within about +/- 5% of the optimum value, and sometimes you’ll find that +/- 10% is still perfectly acceptable.

Better analog meters will have a mirror on their scale.  This enables you to directly line up the angle between yourself, the needle, and the scale and avoid any parallax errors when reading values from the scale.  The bigger the scale on an analog meter, the more accurate the readings you can get from it.

A possible exception to our suggestion you don’t need a lot of accuracy would be reading the voltage of your input power supply.  Noting that power varies according to the square of the input voltage, if your voltage varies by only 10% from specification, the power available to your device will vary about 20%.  That can lead to not-obvious problems that end up burning out motors and frying electronics, so you probably want a meter that has reasonably good accuracy on whatever scale you’ll use to measure input voltages into devices.

One type of accuracy is important.  Whenever you connect a meter to a circuit, you actually change the nature of the circuit, and so the reading you get from the meter will be influenced by the fact that the meter has been connected to the circuit.  This is not really a worry when working on mains level voltages and multi-amp currents, but it can become significant when working on very low voltage and very low current electronics.  Most digital meters are very much better than most analog meters in this respect; if you are getting an analog meter, make sure it is rated at 20 kOhms/volt or higher (a measure of the impact of the meter on the circuit it is testing).  Digital meters should have an impedance of at least 1 Megaohm, and 10 MΩ would be better.

Analog or Digital Multimeters?

A great value analog meter, the Mastech YX360.

A great value analog meter, the Mastech YX360.

The big question you need to answer is whether you should get an analog or digital meter.  Analog meters have an ‘old fashioned’ dial and needle that moves across it, and digital meters of course have a digital digit display.

For an uncertain future, you should use as low-tech a product as possible.  An analog meter would be the best way to go in such a case, because it has almost no electronics at risk of being ‘fried’ by an EMP, and it does not require any power to read volts and amps (but it will unavoidably need a battery to be able to read resistances, due to the way that resistances are tested).  On the other hand, digital meters are very much nicer and more convenient and flexible, all of which is dangerously tempting!

Talking about batteries, make sure your meter uses a typical/common battery and voltage.  Don’t be tempted to go out and buy a lovely old antique Avometer, for example.  Although we have one ourselves, it is more as a museum/display piece than an everyday part of our test gear, because it uses a unique type of 15V battery that is, for all practical purposes, no longer available.

The higher the meter’s battery voltage, by the way, the better it will be able to measure high values of resistance.

A great value fully functioned digital meter, the Mastech MS8268.

A great value fully functioned digital meter, the Mastech MS8268.

Digital meters of course need power (usually from their battery) for everything they do, but their power needs are very low, and we find that the batteries in our digital meters last years at a time.

Interestingly, whereas analog meters are possibly more electrically and electronically robust, digital meters are more physically robust.  If you drop your analog meter, you might destroy it (the indicator needle is on a very sensitive bearing), but if you drop your digital meter, you are much less likely to harm it.

Digital meters have a lot going for them.  Better ones have auto-ranging, so you don’t have to worry about frying the meter by setting it too sensitively for whatever you are measuring.  They are generally a bit more accurate than analog meters too, but see our comments about accuracy above.  On the other hand, some people like to be able to see the swing of a needle which can sometimes help you better understand exactly what you’re seeing when troubleshooting, and of course this is only possible with an analog meter.

Digital meters usually have auto-polarity, so there’s no need to hassle over connecting the positive lead to the positive side of a circuit, and the negative lead to the negative side.  Better analog meters will have a polarity switch so you can simply slide the switch rather than reverse the leads if you get it wrong.

Some digital meters will have added functions such as ‘hold’ which locks in the display the value when you pressed the hold key.  That way if you forget it, you don’t need to remeasure because it is still on the display.  Sometimes you might also see the ability to capture minimum and maximum values, too.  This can be helpful, particularly if you are not staring nonstop at the meter, and have a problem you think might be due to occasional spikes or drops in power.

An auto-off feature is really nice – it saves you if you forget to turn the meter off; you don’t have to worry about running your battery dead.

If you are getting a digital meter, make sure it has a light switch on it so you can turn on a backlight and read the LCD display if you are somewhere with low ambient light.

So, yes, there are lots of benefits to getting a digital meter.  Our suggestion, noting how inexpensive both digital and analog meters are these days, would be to get one of each.  That also allows for the adage that a well prepared prepper has at least two of everything essential and important.

Which One to Buy?

Here’s a listing of analog multimeters from Amazon.  We’d probably choose the Mastech YX360 as a great value analog meter.  It seems to also be sold under different names by other companies, too, but generally at a slightly higher price.

Here’s a listing of digital multimeters, also from Amazon (of course).  You’ll see some units for under $10, but we’d probably splurge and spend not quite $30 to get this truly impressive Mastech MS8268 meter.  Indeed, although we have a shelf full of meters already, we liked this meter so much that we went out and bought one while writing this article!

High Current Ammeters and Clamp Meters

The Mastech $45 AC and DC clamp meter.

The Mastech $45 AC and DC clamp meter.

A problem that is common to most analog multimeters is that they have difficult reading high amp values, because they are built around a meter that is very sensitive, rather than one which is very insensitive, to current flows.

An inconvenience that is also common to all regular meters, is that to read the current flow – the amps – in a circuit, you need to cut the circuit open and connect the ammeter in series with the circuit.  When testing volts, you simply place the voltmeter in parallel across the circuit, which is usually a much easier thing to do.  (Oh yes, as for testing resistances, that can be the biggest hassle of all, because you have to isolate the thing you are testing from everything else before you can get an accurate reading.)

There are of course solutions to these issues.  You can get dedicated high-current reading ammeters and connect those in series in such circuits.  Or, in the case of AC current in particular, you can get a ‘clampmeter’ which is a device that you simply place around one of the wires.  The clampmeter senses the magnetic field created by the flowing AC current in the wire, and so displays the measured current in the wire without you needing to penetrate/cut the wire at all.

Due to the way they work, they are not so good at measuring small amounts of current (ie under one amp) but they are excellent for measuring large currents, potentially up to several hundred amps.  They are also inexpensive, and of the ones listed on Amazon at present, we think this one is probably the best buy (ie just under $30, and with scales all the way up to 600A) for most people and purposes at present.  There are other meters costing very much more, but offering not much extra in the way of useful features for most of us.

There is one feature which some of the more expensive clamp meters offer.  That is the ability to read DC current as well as AC current through the clamp.  If you might find this worth paying only a little extra for, something like this Mastech meter is probably a good choice, and still costing less than $45.

These are wonderful devices, but note they only work when placed around one of the wires in what is usually a two and sometimes three or four wire circuit.  If you place it around both wires in a typical AC power lead, the magnetic field from one of the wires is essentially cancelled out by the field from the other wire, so you will need to somehow separate the wiring to put the clampmeter around one of them.  You might find a very short extension cord where you’ve opened up the wiring between the male and female ends, allowing you to then clamp around whichever wire you wish, will be helpful in such cases.  (In theory, of course, you’ll get the same current reading from either the phase or the neutral wire, and hopefully you’ll get absolutely no current reading at all from the ground wire.)

There is another approach to this – there are wonderful line splitter devices such as this one on Amazon that not only split the line for you, but also have an extra section of line where the current signal is amplified ten-fold, enabling your clamp meter to pick up and display lower currents (for example, a 0.1 amp current would then read as 1.0 amps on the clamp meter).  At a cost of less than $15, this is a very useful thing when testing AC power around your retreat.

Summary

We suggest all preppers should have at least one multimeter as part of their tech/troubleshooting supplies.  If you are buying only one meter, and primarily for electrical purposes, perhaps buying a simple analog meter will not only save you money but also give you the most ‘future proof’ device.  But if you want vastly more capabilities, then you’ll probably choose to treat yourself to a digital meter as well.  And don’t forget a clamp meter too.

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David Spero[suffusion-the-author display='description']

  2 Responses to “A Test/Troubleshooting Multimeter for Preppers”

Comments (2)
  1. I keep a pair of good old 260 Simpsons in my workshop being a starter/ alternator repair guy there isn’t a day gets by that I don’t reach for them

    • Hi there, Mr Fixit

      You sure can fix things with a Simpson 260. They are another classic design, and seem to have held their value much better than the Avometers – perhaps because they are still made. I wonder how long they can hold out against the cheap Chinese imports (Simpson meters are made in WI).

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