"WHAT IS ANALOG MULTI-TESTER AND DIGITAL MULTI-TESTER?"

Analog Multimeters

                           Analog multimeters are electrical test instruments which are used to measure voltage, current, resistance, freuency and signal power.

Analog multimeters use a needle along a scale. Switched range analog multimeters are very cheap but are difficult for beginners to read accurately, especially on resistance scales. Each type of meter has its advantages. Used as a voltmeter, a digital meter is usually better because its resistance is much higher, 1 M or 10 M, compared to 200 for a analog multimeter on a similar range. On the other hand, it is easier to follow a slowly changing voltage by watching the needle on an anlaogue display. Used as an ammeter, nalog multimeters have a very low resistance and is very sensitive. More expensive digital multimeters can equal or better this performance. Most modern multimeters are digital and traditional analog multimters are becoming obsolete.

The basic functionality of an analog multimeter will include measurement of electrical potential in volts, resistance in ohms, and current in amps. Analog multimeters can be used to find electronic and electrical short circuit problems. Advanced analog multimeters come with more features such as capacitor, diode and IC testing modes. Specific measurements made by analog multimeters include DC voltage, AC voltage, DC current, AC current, frequency range for AC currents, and decibel measurement. Analog multimeters that measure current may have a current clamp built-in or configured as a probe. A current clamp is a sensor that clamps around the wire. When searching for analog multimeters it is important to consider the measurement range for whichever value is being measured. An analog multimeter displays these values via a dial, typically a moving pointer or needle. Analog multimeters are generally bench top or hand held. Bench top models can also be portable by use of handles and wheels. Hand held multimeters are specifically designed to be used while holding, i.e, can be operated with one hand.

Analog multimeters have multiple scales on the dial, a moving needle and many manual settings on the function switch. It’s tricky spotting the correct scale to read on the dial, plus you sometimes have to multiply the reading by 10 or 100 to get your final value. Depending on features (make sure it can do continuity testing), prices start at about $15.

For appliance and electronic repairs, it may be better to purchase a digital, not analog, multimeter. This type is much simpler to read and you can change the functions on it more easily. Digital multimeters (Photo 2) have LCD readouts, do continuity testing, and cost from $35 on up. Some digital multimeters also feature auto-ranging and overload protection and other advantages analog multimeters lack.

For easier, hands-free viewing, choose an analog multimeter with a stand that will prop it up or hang it on a wall. If an analog multimeter doesn’t come equipped with either jumper wires or alligator clips (both about $4 each), buy them. Alligator clips are often used to firmly grip wiring or contacts for hands-free safe and accurate readings. Both types of multimeters and these accessories can be purchased at electronics stores, home centers and hardware stores.

Common features for analog multimeters include battery power, overload protection, temperature compensated, mirrored scale, range switch, diode test, and battery test. Devices with battery power can be operated without plug in power. Multimeters with overload protection have a fuse or other method to protect meter. Temperature compensated devices have programming or electrical devices designed to counteract known errors caused by temperature changes. A mirrored scale makes it easier to read the instrument to a given accuracy by enabling the operator to avoid parallax errors. A range switch is used to select appropriate range of units to be measured. A device with a diode test has methods for testing diode operation. A device with a battery test has methods for testing battery operation. An important environmental parameter to consider when searching for analog multimeters is the operating temperature.

Digital Multimeters

                      Digital multimeters can solve most electrical problems - at the hands of a qualified electrical test profession. In fact, With a good wiring diagram and a good meter, a trained electrical professional can find the cause of almost any problem.

There are two basic types of multimeters, digital and analog. Analog multimeters have a needle and DMs have an LCD or a LED display. WIth today's demand for accuracy in testing electrical systems, it makes more sense to have a digital multimeter but an analog multimeter still has its uses.

This article focuses on DMs. A DM will have many functions built into it. As with any tool or piece of equipment, it is necessary to make certain you read and follow digital multimeter instructions and cautions. This will protect you and your electrical equipment.

They will test for voltage, current and resistance. These are the three functions needed when trying to diagnose a problem. When you purchase a digital multimeter, one of the most important things to look at is the meter's impedance, which is the meter's operating resistance. Most digital multimeters have very high impedance. Since the meter is part of the circuit being tested, its resistance will affect the current flow through that circuit.

Typical Amperage Test

Digital multimeters can have very high impedance or resistance and they will cause a slight increase in the circuit's current. This becomes a concern when you test electronic systems because the increased current draw can damage the components being tested or, at the very least, alter the readings or change a sensor signal. It's best to get a meter that has an impedance of at least 10 megaohms. That way the current draw is so low it becomes invisible.

Almost all meters have an "auto-range" features that will automatically select the proper range. Some meters will let you override this feature and let you manually select the range you want. Some DMMs do not have this option and must be set manually. Check the documentation that came with your digital multimeter and make sure you know and understand its different ranges.

Most meters that have an auto-range will have the setting either before or after the reading. Ohms are measured in multiples of ten and given the designation 'K' or 'M' with 'K' standing for 1,000 ohms and 'M' standing for 100,000,000 ohms. Amps would be displayed as mA, milliamps or 1/1000 of an amp or A for full amps. Volts will also be displayed as mV or volts. When you take a reading with a DMM that has auto-range, be sure you note at what range the meter is on. You could mistake 10 mA as 10 amps.

Typical Voltage Test

Most DMs that have auto-range will show the reading with a decimal point. A reading of 1.2 amps will be 12 amps if you ignore the decimal point.

Digital Multimeters do have a limit on how much current they can test. Usually this limit is printed at the point where the red lead plugs into the meter. If it says, "10 Amps Max" then there is a 10-amp fuse inside the meter that will blow if the current is above 10 amps. If you take out the 10-amp fuse and put in a 20-amp fuse, you will burn out the meter beyond repair. I would suggest buying a DMM that will handle at least 20 amps for automotive testing.

Typical Resistance Test

Another useful function of the DM is the ohmmeter. An ohmmeter measures the electrical resistance of a circuit. If you have no resistance in a circuit, the ohmmeter will read 0. If you have an open in a circuit, it will read infinite.

An ohmmeter uses its own battery to conduct a resistance test. Therefore there must be no power in the circuit being tested or the ohmmeter will become damaged.

When a component is tested, the red lead is placed on the positive side and the black lead on the negative side. Current from the battery will flow through the component and the meter will determine the resistance by how much the voltage drops. If the component has an open the meter will flash "1.000" or "OL" to show an open or infinite resistance. A reading of 0 ohms indicates that there is no resistance in the component and it is shorted. If a component is supposed to have 1,000 ohms of resistance and a test shows it has 100 ohms of resistance, which indicates a short. If it reads infinite, then it is open.