ANALOGUE AND DIGITAL MULTIMETERS

ANALOGUE AND DIGITAL MULTIMETERS

ANALOGUE MULTIMETERS:

Analog multimeters use a needle along a scale. Analogue multimeters are electrical test instruments which are used to measure voltage, current, resistance, frequency and signal power.

Functions:
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.

Construction:
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),

Common Features:
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.

DIGITAL MULTIMETERS:
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.
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.
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.
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.

MULTIMETER:

                   A multimeter or a multitester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. There are two categories of multimeters, analog multimeters and digital multimeters.

ANALOGUE MULTIMETER:

                   Resolution of analog multimeters is limited by the width of the scale pointer, vibration of the pointer, the accuracy of printing of scales, zero calibration, number of ranges, and errors due to non-horizontal use of the mechanical display. Accuracy of readings obtained is also often compromised by miscounting division markings, errors in mental arithmetic, parallax observation errors, and less than perfect eyesight. Mirrored scales and larger meter movements are used to improve resolution; two and a half to three digits equivalent resolution is usual (and is usually sufficiently adequate for the limited precision actually necessary for most measurements).
Resistance measurements, in particular, are of low precision due to the typical resistance measurement circuit which compresses the scale heavily at the higher resistance values. Inexpensive analog meters may have only a single resistance scale, seriously restricting the range of precise measurements. Typically an analog meter will have a panel adjustment to set the zero-ohms calibration of the meter, to compensate for the varying voltage of the meter battery.
Accuracy:

Analog multimeters typically measure with about three percent accuracy. Mainstream bench-top multimeters make claims to have an accuracy of better than ±0.01%. Laboratory grade instruments can have accuracies in the parts per million figures. A multimeter's quoted accuracy is specified as being that of the lower (mV) DC range, and is known as the "basic DC volts accuracy" figure. Higher DC voltage ranges, current, resistance, AC and other ranges will usually have a lower accuracy than the basic DC volts figure.

DIGITAL MULTIMETER:
              The resolution of a multimeter is often specified in "digits" of resolution. For example, the term 5½ digit refers to the number of digits displayed on the readout of a multimeter.
Modern multimeters are often digital due to their accuracy, durability and extra features. In a digital multimeter the signal under test is converted to a voltage and an amplifier with electronically controlled gain preconditions the signal. A digital multimeter displays the quantity measured as a number, which eliminates parallax errors.
By convention, a half digit can display either a zero or a one, while a three-quarters digit can display a numeral higher than a one but not nine. Commonly, a three-quarters digit refers to a maximum value of 3 or 5. The fractional digit is always the most significant digit in the displayed value. A 5½ digit multimeter would have five full digits that display values from 0 to 9 and one half digit that could only display 0 or 1.
 While a digital display can easily be extended in precision, the extra digits are of no value if not accompanied by care in the design and calibration of the analog portions of the multimeter. Meaningful high-resolution measurements require a good understanding of the instrument specifications, good control of the measurement conditions, and traceability of the calibration of the instrument.
Accuracy:
              Digital multimeters generally take measurements with accuracy superior to their analog counterparts. Standard portable digital multimeters claim to be capable of taking measurements with an accuracy of 0.5% on the DC voltage ranges.