In my opinion, the most important, and first piece of equipment any shop should have is a good digital Multimeter (DVM). This will measure all of the basic units (AC & DC Volts, Ohms, Current) and will serve as a reference standard for your other equipment. Most units will also have additional abilities to measure things such as Capacitance, conductance, frequency, etc. You will use this meter constantly so invest in a good one, and do not forget to get one rugged enough for the conditions you work in! I highly recommend Fluke as they are nearly "bulletproof" both electrically, and physically. And stay away from "imports"!! Their accuracy, especially for ohms and amps, is much worse than the Big brands. They also tend to suffer extreme damage if you try to measure something on the wrong range. I have also heard of some of these literally exploding from surges when being used in power applications. Fluke meters are also IEC Category rated for use in High power and High Voltage circuits. If you work in these areas. look at this page from the NECA/IBEW training site: http://www.nietc.org/templates/template2/template2.php?page=99
Although I normally advocate surplus equipment, in this case, I would avoid used ones. Quality Digital Meters are very available and affordable. This is one instrument you need to be able to depend on completely, and you don't want to have to fix (or calibrate) it!
Pictured above is my favorite. It is a Fluke 8060A. It is rugged, accurate and dependable.
I suggest a meter with a 4 or 4 1/2 digit display. This should provide sufficient resolution and range for any of your experimenting, repair and hobbyist activities. As for accuracy, any Name brand (Fluke, Simpson, Triplett, Agilent (HP), Kiethley, Tek, etc) will have more than sufficient accuracy. A 200 mv range is a necessity, and it should measure up to at least 600 volts AC&DC (750 is common). For current, look for at least a 2ma to 2A range, A 10 amp range is common, and can be very useful
I prefer to avoid autoranging like the plague. Instead get a meter with a lot of ranges, selectable by a knob, or Push Buttons. In Experimenting, you are often dealing with completely unknown values. Autoranging adds a level of Ambiguity. It also slows down readings, and is very hard to apply to changing measurements.
Make sure! Most good meters will withstand voltages up to their maximum range on any range setting, but Check! Make sure the Ohms function is protected against voltage, and the higher AMP ranges should be protected by a fuse.
Another very useful feature, but make sure it does not shut off for at least 10-20 minutes!
Get a good meter in a rugged case with a recessed display, and protected switches. Any protruding switches or knobs WILL get damaged. The case should be of a quality "vinylized" resilient plastic. If it is made of a hard and brittle plastic - you WILL break it! Companies such as Fluke also offer "Ruggedized" meters, and protective rubber case guards. If you anticipate using it in an industrial setting, or to fix cars, this is a very worthwhile feature.
Sounds silly, but, especially if you carry this meter in a tool bag, MAKE SURE the power switch is recessed, and cannot be accidentally nudged, and no push button power switches! My years in field service have served to burn this into my brain. Nothing like a dead battery to spoil the day!
Most meters come with banana jacks that accept fully insulated leads, and this is good! But, make sure you can plug in a normal banana plug as well. This will be necessary eventually. Also, I prefer to avoid anything with a "proprietary" test lead connector. You will want to occasionally use other test leads.
|From time to time, you will need an analog VOM. It is hard to measure a slowly changing value with a digital meter, and they are absolutely necessary for tuning, peaking, nulling, etc. The Old standby, pictured on the right is the Simpson 260. This is an old one. Simpson makes newer versions of the 260 (260-8) with more features. These meters have no active devices, and have a low input impedance (20k Ohm/Volt). The low input impedance will greatly affect measurements of lower voltages due to circuit loading. It is a benefit sometimes around machinery or other equipment in that it will effectively ignore stray noise. The other analog option is variously called a "transistorized" VOM (TVM), a FET VOM, or a VTVM (The original used vacuum tubes, hence Vacuum Tube Volt Meter). These meters use active amplifier circuits, and have very high input impedance (10 mohm). This is often achieved in part with a "special" test probe that has a built in 10 mohm resistor. Pictured on the left is a Triplett 601. This is a very old model, and had some problems with battery holders and count (12 AA Cells). There are also Hybreds, Digital meters with additional Analog scales. The analog scales on these are often very slow reacting, and I find them of limited value.|
|These meters are available used, on Ebay and as surplus. This is a viable source for these as accuracy, being lower, is not as great a concern and they are much simpler to repair than a Digital meter. I would suggest the Simpson 260 if you plan to do much Electrical or industrial work (or work around RF Transmitters). It is still the standard bearer in those areas due to its reliability, ruggedness, versatility, and aforementioned noise immunity. Be warned, they are still a bit pricey because they are still in demand. If your need is for aligning things, absolute accuracy is not as important, and you would do just as well with one of the more inexpensive transistorized versions (TVM) from places such as MCM Electronics, Ramsey, Digi-Key, etc. Look at the input impedance to certify it is a true TVM. It should be around 10 MegOhm per volt or above.|
|Finally, a comment on the "big ticket stuff". Pictured at right is my Fluke 8800 Bench/Lab meter. 5 1/2 digits, super accurate, and super expensive. This used to be a prize! I acquired this when digital voltmeters were much more rare, and many were chintzy. It plugs into the wall, has limited ranges, and doesn't do AMPS. I can't remember the last time I used it!! You do not need a meter like this for hobby work, or anywhere outside of an R&D Lab. Being Mister Retro, I hate to say it, but, Save your money, and apply it to a good modern handheld.|
These simply do not need much maintenance! Change the batteries, and don't leave them in it forever, they still leak eventually! Keep it clean, and adjust the Zero on an analog one. Change the leads if they are frayed (experience talking). Speaking of that, try to keep test leads with insulated plugs. Some Banana plugs have exposed metal around their bottom, and you will end up touching it at some inopportune time! DO NOT try to calibrate one of these. A modern meter will hold an acceptable calibration for a long time, and it will still be better than whatever you have to compare it to.