Multimeter

A Multimeter is a versatile equipment for measurement of different electrical quantities in a circuit. In the course of lab work it is often required to measure voltage, current and resistance. Instead of using three different meters it is better to use a Multimeter. The Multimeter is equipped with circuitry that allows it to be used as a voltmeter, an ohmmeter or as an ammeter. That is the reason why a Multimeter is also known as Volt-Ohm-Milliammeter (VOM).

Constituents of a Multimeter

• Probes : Probes is used for connecting the Multimeter into the circuit. With Probes, connections are simply touched for measurement and the Multimeter gives the readings.
  
  Depending on the voltage or current to be measured, a variety of Probes are used. As a rule higher the current higher would be the number of probes between the probes and thicker the cables.
  
  
• Ports : One of the question which puzzles the users of Multimeter is that there are only two probes whereas there is number of sockets. A diagram of the ports is shown here. The diagram shown here is of a Multimeter with four probes. This is not a standard design, a Multimeter can have more or less ports. Let's understand the function of each of the ports.
  » Number 1 is the common port.Normally, the black probe is plugged here (negative). Truly according to the name it is a common element to all of the testing circuits.
  » Number 2 is the voltage, resistance and continuity port. The red probe(positive) is connected to this port for voltage and resistance readings or for checking of wire continuity.
  » Number 3 is for current up to 300mA and is used for counting electrons in a circuit.
  » Number 4 port does the same work as above but can take more current up to 10A
• Symbols :Some of the common symbols found in the knob of a Multimeter is discussed here.
  » Alternate Current : The symbol depicted here is of AC current. This is turned for testing that has an AC current running through.
  
  » DC :This is the symbol for direct current.
  
  
  » Continuity : This great for checking continuity and checking for shorts. When current is put through two terminals, and if the resulting value is within the contact range it will beep or give light indication.
  
  » Resistance : This is the symbol for resistance, and its unit is in Ohms. Using this setting the resistance between two points can be measured.
  
  » Voltage : This is for measuring the potential difference between two probes. For measuring voltage the positive probe is connected to a port marked as “V” or Voltage.
  
  » Current : This has the symbol of “A” called Amps. This measures the current flow in the part of circuit between two probes.

Types of Multimeter
Analog Multimeter
Analogue multimeters utilizes very little power from the circuit to be tested for operating of the pointer . Analogue Multimeter should have a high sensitivity that is minimum 20kO/V. Anything below this can upset the circuit to be tested and give rise to an incorrect reading. For obtaining a valid reading the meter resistance must be at the minimum 10 times the circuit resistance. While looking for Analog Multimeter a crucial environmental parameter to consider is the operating temperature. Some of the features to look for in Analog Multimeter includes the following:

• Battery power
• Overload protection
• Temperature compensation
• Mirrored scale
• Range switch
• Provision for Diode and battery test

Digital Multimeter
A Digital Multimeter display a constant resistance that is at least 1MO (often 10MO) applicable on all their DC voltage ranges. This is often more than sufficient for almost all the circuits.

A Digital Multimeter is a versatile instrument that contains three meters namely ammeter, voltmeter and ohmmeter. Digital multimeters are now coming in different types of models such as bench top or handheld. If used with handles and wheels bench top models can also be portable. Handheld multimeters can be operated with a single hand. Some of the features to look for in Digital multimeter include the following:

• Battery power
• Analog bar graph
• Data acquisition and storage
• Data logging
• Auto-ranging
• Adjustable sampling rate
• DB readings
• Removable data storage

Layout of a Digital Multimeter
A Digital Multimeter is designed to contain the Digital display panel on the top which can display any number between 0 to 1999 or even higher. Below the digital readout area is a knob called the function switch. With this switch the Digital Ammeter can perform different functions. After the knob is the ports where the probes are connected for taking readings.