The Complete Multimeter Buying Guide

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The Complete Multimeter Buying Guide

A multimeter combines three electrical testing tools in one: a voltmeter, an ammeter, and an ohmmeter. It measures electric voltage, current, and resistance. They are used in testing such items as batteries, automotive electrical systems, electrical components, circuits, switches, power sources, and motors. Registered electricians as well as those working in auto shops, labs and other technical environments use them to diagnose and resolve malfunctions in electrical systems.

Multimeters available in the market vary first according to whether they are digital or analogue and then according to the range of values they are designed to read. The latter determines what kinds of devices a specific multimeter is suited to test, from household batteries to automotive electrics. Various multimeters also offer specific features that make them more useful for certain tasks.

An oscilloscope attachment allows for a read-out of fluctuations over time. A temperature sensor can be a helpful addition when metering computer components that are temperature sensitive. A buyer who takes into account the various issues that make multimeters more or less useful for specific circumstances is sure to find the multimeter best for his or her specific needs in the large eBay marketplace.

Three Uses of a Multimeter

Multimeters are used to run three kinds of tests on electrical circuits, components, and systems. They measure voltage, resistance, and current, as follows.

Measuring Volts

As a voltmeter, a multimeter measures the potential difference in electrical energy, or voltage, between two points. This is the most common test of an electrical system and essential requires simply touching the meter prongs to two different points of the system. The meter measures the difference in energy at the two points without changing the circuit.

Measuring Resistance in Circuits

As an ohmmeter, a multimeter measures the resistance a particular element in a circuit offers to electrical flow. To do this, the element must be removed from the circuit for individual testing. Attempting to test it in a circuit attached to a power supply could damage the meter.

Measuring Current in Closed Circuit

An ammeter measures current in a circuit as part of the circuit. That is to say, the meter itself must become part of the circuit by breaking the circuit to include the meter so current flows through the meter.

Different Kinds of Multimeter

When selecting among multimeters, one of the first decisions to be made is whether a digital or analogue model is preferred. Beyond this, a number of issues are to be decided related to the multimeter's capacity and its anticipated uses.

Digital vs. Analogue

Digital multimeters differ from traditional analogue multimeters in several ways, including how readings appear, the level of accuracy achieved, and the potential for downloading readings to a computer. The read-out on a digital multimeter appears on an LCD screen. These decimal read-outs are unequivocal. The accuracy is considered to be within 1 per cent for DC and within 2 per cent for AC. Readings from digital multimeters may be downloaded to computers for later review and analysis. Those multimeters with oscilloscopes provide a wealth of time-linked data.

Analogue meters provide a reading that is less easy to read because the device display shows a bar along a numeric scale. The user interpolates values between the marked numbers to obtain an accuracy that is considered to be within 2.5 per cent.

Multimeters for Different Uses

The sensitivity range of a multimeter designates the highest and lowest inputs the meter can read. Generally speaking, this sets the kinds of applications that are appropriate for a specific multimeter. The automotive multimeter that is able to read the high voltages of an automotive battery is not going to have a sensitivity range broad enough to also read low-voltage power sources. This means that the purchaser needs to know how he or she intends to use the multimeter when selecting one:

  • Checking fuses, batteries
  • Testing incandescent bulbs
  • Testing transistors
  • Testing integrated circuits
  • Testing light switches
  • Troubleshooting automotive electronics
  • Troubleshooting boiler electrics

Different multimeter uses require different sensitivity ranges. The low voltages in integrated circuits cannot be tested using a multimeter designed to test the higher voltages in automotive systems. A multimeter for automotive electronics is often labelled as an auto multimeter or marketed as garage equipment.

Digital Multimeters with Oscilloscopes

Multimeters with oscilloscopes allow readings to be recorded over time. This is a useful function when it is important to know how the readings for a particular piece of equipment may have fluctuated during a given period. Both digital and analogue multimeters can be equipped with oscilloscopes, but only digital models offer the potential to download the data to a computer for storage and review.

Other Features to Consider

A number of specific features that are important in the selection of a multimeter are referenced below. Some, such as sensitivity range, are general to the selection of any multimeter.

Feature

Function

Benefit

Autorange

Adjusts multimeter automatically to the measurement range for inputs

Saves time when many tests are being run

Temperature Sensor

Measures temperature of devices

Helpful with such temperature-sensitive hardware as computer processors

Measure Capacitance

Measures a system's ability to store an electric charge

Available on digital multimeters

Transistor Testing Circuits

Checks whether transistor is functioning

Useful in testing digital logic circuits and integrated circuits

Display Rate

Represents speed at which digital display refreshes

Faster display rates mean more accurate readings

"Hold" Function

Keeps the display from changing

Useful when noting readings

Display with Large Digits and Backlight

Designed for ease of use

Easy to read, even in dark crawl spaces and basements where electrical systems may run

ISO or NIST calibration

Indicate compliance for certified companies

Ensures highest levels of accuracy in readings

Calibration to the standards of the International Standards Organisation or National Institution of Standards and Technology is particularly important to companies that hold related certifications. These certifications indicate products made to very rigorous standards, so obtaining multimeters with the correct certificates is important in these cases.

Selecting a Multimeter for Anticipated Loads

Maintaining the correct balance between current needs, anticipated needs, and current budgets is often a challenge. Multimeter costs rise as the kW load they can handle rises. That can make it tempting to economise by selecting multimeters designed to handle the largest load under present operations only. This choice can force an organisation to replace its multimeters much sooner than would otherwise have been required. Thinking a few years ahead allows the organisation to make its multimeter selections for lifecycle cost effectiveness, instead of day-of-purchase lowest price.

Safe Use of Multimeters

The topic of multimeter safety is a bit too large for a guide as brief as this, but two points should be made about how to use multimeters safely in circuits that are connected to the power grid.

Sticking Multimeter Probes into Wall Sockets

If the buyer is sufficiently inexperienced with electricity to ask, as some forum users have, "Is it safe to stick my multimeter probes into wall sockets?" the short answer is: "Not in the U.K." The long answer is: Spend some time with a more experienced person before attempting to use your multimeter. There is an important reason why.

Preventing the Multimeter from Exploding

It seems incredible that an innocuous appearing test device could explode, much less do serious harm. The phenomenon is called "arc blast", and it has more potential causes than can be explained in this short guide. Essentially, a high voltage ionises the air itself between the multimeter's probes so that the air becomes conductive, causing an electric flash that may burn or even kill the user.

An arc blast rips through the air at 140 decibels, as loud as a jet engine at take-off. That means that the least harm to be anticipated is permanent nerve damage to the hearing of the user and anyone nearby. Again, those who are not experienced with electricity need to lean on an experienced friend before using multimeters to test circuits connected to the power grid.

Well-Known Brands

Multimeter users have found many brands offer quality products. Some of the top brands in the field include:

  • Fluke
  • Agilent HP
  • Gossen
  • Sealey
  • Wavetek
  • Sanwa
  • Kyoritsu

Buying a Multimeter on eBay

Many multimeters are offered on eBay by reputable sellers. For buyers requiring ISO or NIST calibrated multimeters, the initial search may include " multimeter ISO" or "multimeter NIST" to locate the specific required devices. Likewise, those requiring multimeters with oscilloscopes may search for "multimeter oscilloscope" and those preferring "analogue multimeters " over "digital multimeters" may also make use of the search function. The "automotive multimeter" tends to cross categories and is worth a separate search among products listed as garage equipment.

Selecting a Seller with Confidence

To be confident in the equipment being purchased, some people prefer to purchase from eBay top-rated sellers. These are sellers with a significant record of successful sales and quality customer service. Among multimeter vendors, they serve the low-price to mid-range market.

Top-end certified devices are typically sold by prior owners who may be new to eBay. Any lack of an eBay ranking should not automatically discount them as sellers. A buyer may wish to use the "Ask a question" feature on the product page if anything seems unclear about the product or its certification.

Conclusion

A multimeter that has been properly selected for the load it is expected to carry is a useful tool for household and industrial applications. It prepares the user to measure volts, current, and resistance in circuit boards, batteries, bulbs, fuses, and other electrical devices. Users may choose among digital and analogue multimeters, each of which has proponents. The digital models permit data download to computers for analysis and to oscilloscopes for viewing change over time.

After this selection, the most important issue to consider is the multimeter's sensitivity range. A multimeter designed for a high voltage range, such as those in automotive electrical systems, is not able to read the low voltages in household batteries or typical circuit boards. Similarly, a multimeter designed for readings in an electrical power grid has a range too high for power that has been stepped down for ordinary use.

Several other features of value may be considered, including additional sensors that may be available on the multimeter and whether it has been calibrated for certified industrial use. When these factors are taken into consideration, it is easy to find a multimeter on the eBay marketplace that meets the user's needs.

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