AVO multimeters were almost ubiquitous in British manufacturing and service industry, research and development and higher and further education. They were also widely used by utilities, government agencies and the British armed forces. A number of special versions were produced to British Admiralty and Air Ministry specifications and for other customers. The Model 8 Marks V, 6 & 7 were designed to meet a NATO specification and were standard issue to NATO services. Many commercial and military service manuals specified that values for measurements of current or voltage had been made with a Model 7 or Model 8 AVOmeter. Advertisements of the late 1930s compared the utility of the AVOmeter to the slide rule. Even nowadays it can still be found in regular use.
The earlier versions of models 7, 8 and 9 had a design flaw which resulted in many instruments sustaining damage to the movement in transit. Users would habitually 'switch off' the instrument by setting the AC switch to 'DC' and the DC switch to 'AC'. With the switches at these settings, the movement is completely undamped.[14] The operating manuals for the affected instruments did contain a note that they should not be switched to 'AC' and 'DC' (or the blank position either side of the 'AC' and 'DC') though failed to explain why.[15] The problem was solved on later instruments by providing the DC switch with an 'OFF' position (see illustration above).
Avometer 8 Mk 6 Manual
Some multimeters also have a diode check function. A diode is like a one-way valve that only lets electricity flow in one direction. The exact function of the diode check can vary from multimeter to multimeter. If you're working with a diode and can't tell which way it goes in the circuit, or if you're not sure the diode is working properly, the check feature can be quite handy. If your multimeter has a diode check function, read the manual to find out exactly how it works.
Advanced multimeters might have other functions, such as the ability to measure and identify other electrical components, like transistors or capacitors. Since not all multimeters have these features, we will not cover them in this tutorial. You can read your multimeter's manual if you need to use these features.
Some multimeters are "auto-ranging," whereas others require you to manually select the range for your measurement. If you need to manually select the range, you should always pick a value that is slightly higher than the value you expect to measure. Think about it like using a ruler and a yardstick. If you need to measure something that is 18 inches long, a 12-inch ruler will be too short; you need to use the yardstick. The same applies to using a multimeter. Say you are going to measure the voltage of a AA battery, which you expect to be 1.5V. The multimeter on the left in Figure 3 has options for 200mV, 2V, 20V, 200V, and 600V (for direct current). 200mV is too small, so you would pick the next highest value that works: 2V. All of the other options are unnecessarily large, and would result in a loss in accuracy (it would be like using a 50-foot tape measure that only has markings every foot, and no inch markings; it isn't as accurate as using a yardstick with 1-inch markings).
You might have noticed some other symbols besides V, A, Ω, and metric prefixes on the front of your multimeter. We'll explain some of those symbols here, but remember, all multimeters are different, so we cannot cover every possible option in this tutorial. Check your multimeter's manual if you still can't figure out what one of the symbols means. You can also browse our multimeter gallery to see labeled pictures of different multimeters.
Your multimeter probably came with red and black wires that look something like the ones in Figure 4. These wires are called probes or leads (pronounced "leeds"). One end of the lead is called a banana jack; this end plugs into your multimeter (Note: some multimeters have pin jacks, which are smaller than banana jacks; if you need to buy replacement probes, be sure to check your multimeter's manual to find out which kind you need). The other end is called the probe tip; this is the end you use to test your circuit. Following standard electronics convention, the red probe is used for positive, and the black probe is used for negative.
The diode check feature is useful to determine in which direction electricity flows through a diode. The exact operation of the "diode check" function will vary for different multimeters, and some multimeters do not have a diode check feature at all. Because of this variety, and because the feature is not required for most Science Buddies projects, we have not included directions here. If you need to do a diode check, consult the manual for your multimeter.
Instructions for changing the fuse vary with each multimeter model, so you will need to check your multimeter's manual for instructions. This tutorial from SparkFun provides directions for changing a fuse on their brand of multimeter, but remember that these directions might not apply to your model. Note that in some multimeters-especially in inexpensive ones-you might not be able to change the fuse.
Remember, this gallery is meant to be a general guide; if you do not see your model of multimeter pictured here, your best bet is to consult your specific multimeter's manual. If you need help getting introduced to multimeters in general, refer back to our Multimeter Overview section. If you need to know how to take a specific type of measurement, refer to the Using a Multimeter section.
2ff7e9595c
Comments