Monday, February 11, 2013

Learn how to use an electrical multimeter - A basic introduction tutorial and multimeter manual


Introduction:

When you get behind the wheel of a car, what is the next thing that you would most certainly do besides closing the door and strapping yourself securely to the seat. Obviously enough, it is expected that you would turn the ignition to start the engine, grab the steering wheel, shift the gear and step on the pedal because this is the most basic routine that every driver would instinctively do to drive a car. This inherent trait almost comes as a second nature to all experienced driver, which simply is an automatic pattern of behavior in reaction to the specific situation of driving a motor vehicle.

Similarly, having an aptitude for using an electrical multimeter would always come in handy when working with electrical circuits. Just as it is vitally important to have a thorough understanding about what makes up the structure of an electrical circuit, which involves the installed electrical switching components that are connected in such a way as to provide a continuous controlled flow of electrical path between the circuit's supply or source voltage down to the connected load in the circuit, so too is the importance of using a multimeter in circuit analysis.


Significance of multimeter with electrical circuits

It is always immediately apparent that possessing an in-depth understanding about any electrical circuit is directly associated with having a practical knowledge on how to check the circuit with a multimeter. And it is also anticipated for this to include knowing the intended purpose of each basic functions and features combined into this single instrument, which should just as well be like a second nature when you develop your electrical skills acquired through frequent repetition of doing the same standard procedure of using the instrument over time.

Analog Multimeter
Typical Analog Multimeter
An electrical multimeter is the most indispensable instrument that you will have to habitually rely on when diagnosing electrical faults. But how well you are able to analyze and determine the cause of the electrical failure to come up with a solution to fix the fault depends entirely on your ability to competently use and interpret the readings on the multimeter.

If you are a beginner who's just starting to learn how to use a multimeter, the best way to find out about the proper method of operation of the specific multimeter you are about to use is to get firsthand instruction about the instrument by referring to the multimeter's users manual.

But if all you need is a quick reference guide on the basic usage and fundamentals concerning the operation of the multimeter instead of consuming a lot of time in understanding the detailed specifications by painstakingly skimming through all information including the optional descriptions specified in the multimeter manual page by page, which are mostly printed in small difficult to read font sizes anyway, then I would suggest for you to carry on reading this article where you will find a simple easy to understand instruction which will walk you through the necessary steps to learning the basic procedure on the usage and functionality of an electrical multimeter.

What is a Multimeter - the basics

There are many information you can find that will teach you things you need to know about how a multimeter works, in fact you will find a lot of learning tips about the intricate details of each type of multimeter just by searching from the internet.

Now what is presented here in this article are not the only factors you need to consider about multimeters since different models and brands are designed with assorted variations of functions and features. But for the purpose of providing a basic idea to help you understand, the information provided on this site will suffice.

An electrical multimeter is a test meter specifically designed for AC (alternating current) and DC (direct current) electrical and electronic circuits. It is basically a multifunction meter consisting of the three important variables comprising the electrical formula for the ohms law equation, which are the voltmeter for measuring voltages, the ammeter to measure current, and the ohmmeter to measure resistance, all combined into a single useful instrument.

In order to get the best possible result from the multimeter, it is important to know the correct application of the multimeter to a selected purpose in order for it to work according to its intended function. And by that it follows that it is important to determine how the meter should be connected in the circuit in relation to the purpose of the selected function of doing the actual measurement.

Types of electrical multimeter


Two Basic Types of Multimeter - Analog and Digital Multimeter
Fig.1 - Two Basic Types of Multimeter - Analog and Digital Multimeter
There are two common types of multimeter, the analog multimeter and the digital multimeter (See Fig. 1). The analog multimeter is distinguished by its distinct appearance of having a dial gauge with a needle which serves as a pointer that moves along a plate marked with fixed intervals of graduated measurement scale where a reading can be estimated, while a digital multimeter is simply identifiable by having a digital LCD display where the measured value is indicated in numerical digits for direct reading.

Deciding on which multimeter is the best alternative for circuit analysis is entirely dependent on your choice of preference. But as you gain more knowledge and experience by developing your skills in the electrical field you will find it more appropriate to have both of them available whenever possible.

In my own personal opinion, however, I would really suggest for beginners to start learning to use the analog multimeter because it is a more effective alternative to potentially develop the tendency of having a strong inclination to learning electrical circuits. I know this firsthand based from my own learning experience, which is the very reason why I am personally recommending its suitability for having the potential of being beneficial to achieving the best possible learning outcome in the long run.

And I must confess that it really did became a workable strategy which had an influential impact on my way of thinking where I further realized why learning to use the analog multimeter is predominantly the best course of direction that cultivates passion that is imperative to learning the basics of electrical circuits.

But despite my predisposition to prefer analog meters over digital meters based from considerable experience, I also have to mention the advantage of modern digital meters for having higher internal input impedance, which provides more accuracy and protection. The high input impedance of the digital meter provides higher isolation so that it does not affect the component under test in the circuit. This very minimal effect on the measurement value of the component being tested makes digital meters an ideal choice for measuring in-circuit electronic components.

But while we can be assured that we don’t have to worry about the circuit when using digital meters, analog meters on the other hand tends to force us to think first about the circuit before we do the actual measurement, which provides more interaction between the user and the electrical circuit, hence providing more learning experience.


Safety Precautions

  • For precision and accuracy, always use fully-charged battery for efficient meter operation.
  • For DC circuits, ensure the correct polarity of the multimeter test leads are selected accordingly before inserting them to the circuit under test (i.e. red lead goes to the positive potential and the black lead goes to the negative potential of the circuit).
  • Before measuring, ensure the jacks on the other end of the test probes are plugged to the correct terminal of the meter. The black lead is always plugged to the COM (common) terminal, the red lead is plugged either to the A terminal when measuring current and V terminal when measuring voltage.
  • To prevent electric shock, always be very cautious and attentive when measuring mains AC voltage or any high voltages.
  • Do not use defective or damaged test leads.
  • Always put your fingers on the insulated part of the test probes, do not touch the tip of the probes when measuring live circuits.
  • Do not use the meter on live circuits beyond the rated capacity of the multimeter.
  • Do not put the test probes into the circuit unless you are entirely sure you have chosen the correct function (i.e. V for voltage, A for amperes, and Ω for ohms), and that the appropriate range for the chosen function is also selected by turning the rotary selector knob of the meter according to the range and function provided on the table below. Note that the following is applicable only for manual ranging meters and not available with auto ranging meters. The advantage of manual ranging meters such as the analog multimeter is that it compels us to habitually think first about the measurement range that we have to select before we do the actual measurement.

Ω (Ohms) DCV (Direct Current Voltage) ACV (Alternating Current Voltage) DCA (Direct Current Amperes)
Ω x100K DCV x 1000 ACV x 750 DCA x 0.25
Ω x1K DCV x 250 ACV x 250 DCA x 25mA
Ω x100 DCV x 50 ACV x 50 DCA x 2.5mA
Ω x10 DCV x 10 ACV x 10 DCA x 50uA
Ω x1 DCV x 2.5
DCV x 0.25
DCV x 0.1

Measuring Voltage

Before applying the multimeter test leads to the circuit to be measured, make sure first that the red test lead is plugged to the V or voltage terminal while the black test lead remains plugged into the COM or common terminal of the meter, this is applicable only when using digital meter (See Fig.2 and Fig.3). Then determine the type of voltage measurement to be made on the circuit in order to decide on the appropriate function and range to set on the meter.

Digital Multimeter DC Volts Function
Fig.2 Digital Multimeter DC Volts Function
Digital Multimeter AC Volts Function
Fig.3 Digital Multimeter AC Volts Function


Voltmeter Connected in Circuit
Fig.4 - In-Circuit Connection of Voltmeter
When using a manual ranging meter, always set the voltage range higher than the target voltage to measure, for example, when measuring AC 120 volts set the meter to the 250 volts range, and when measuring AC 440 volts set the meter to the 750 volts range. Keep in mind that safety is your priority as voltage measurement involves diagnosing live circuit which can lead to electric shock and personal injury. 

With reference to the diagram shown in Fig. 4, after setting the range selector knob of the meter to the appropriate voltage range, connect the test leads in parallel between two points across the component where the potential difference is to be measured. When measuring DC circuits, always make sure the correct orientation on the polarity of the test leads is applied to the circuit, the red lead goes to the positive potential while the black lead goes to the negative potential of the circuit.
Digital Multimeter Ampere Function
Fig.5 Digital Multimeter Ampere Function

Measuring Current

When measuring amperes using a digital meter, make sure that the red test lead is plugged into the A or ampere terminal of the meter while the black test lead should always remain on the COM or common terminal (See Fig.5). Note also that although digital meters may indicate a maximum capacity of 10 amperes, it is rarely ever used with live circuit, instead a clamp ammeter is the best alternative to do the job. Hand-held electrical multimeters are suitable for measuring small amount of current like in measuring 4 to 20 mA (milliamperes) linear currents.

Ammeter Connected in Circuit
Fig.6 In-Circuit Connection of Ammeter

Measuring current in live circuit requires for the meter to be connected in series with the load. This means that a portion of the circuit should be opened where the meter will be inserted in between the circuit to make it an included device as part of the circuit so that it also becomes an electrical path where the current could flow through as shown in the Fig.6.
Before connecting the meter to the circuit, set the meter to the appropriate function range in amperes to prepare it for the correct ampere reading required. For the purpose of safety, power down the circuit to allow working on the circuit while the power is off. Cut a portion of the circuit where the meter will be inserted. Wire the meter to the circuit to establish a series connection, then turn on the power to the circuit to get the ampere reading on the meter.

Measuring current in a live circuit with the multimeter connected in series poses potential electrical shock hazard, this is why most current measurements are safely done with the indirect method by means of using a clamp ammeter.

Measuring Resistance

Measuring resistance does not require the power source supplied to the circuit, because measuring resistance with the power to the circuit energized will cause damage to the meter. It is also necessary for the specific component to be tested for resistance to be isolated from the circuit.

For analog meter, before connecting the meter to the circuit, calibration of the meter is first performed to ensure accuracy of reading. Set the meter to the appropriate function range in ohms to prepare it for the correct resistance reading required. Short the tips of both the red and black test probes together then adjust the 0Ω adjuster knob until the pointer on the dial gauge is aligned to 0Ω on the scale. Digital meters does not require calibration, all you need is just to select the appropriate function and ohms range that is required for the measurement.

For safety reasons, disconnect the power to the circuit altogether to allow working on the circuit while the power is off. After the absence of power to the circuit is confirmed by checking for voltage with the meter, resistance value of the target component can now be measured. Note also that the polarity of the test leads plugged into the meter is similar to the configuration of voltage measurement wherein the red plug of the test lead goes to the V/
Ω (ohms) input terminal of the meter while the black test lead plug goes to the COM or common terminal of the meter.

Ohmmeter Connected in Circuit
Fig.7 In-Circuit Connection of Ohm Meter
Fig.7 shows a typical series circuit equipped with a switch SW1. With the power off, open the switch then connect the meter parallel across the target component to measure its resistance. With the switch opened, an open circuit is established in the system and only the resistance value of the target component is measured disregarding potential resistance reading of the other components in the circuit. If the switch is turned on in the same meter connection, what happens is that the close state of the switch will cause complete series connection flow path in the circuit which will cause the meter to read additional resistance value coming from the internal resistance of the power supply and the lamp.


Ohmmeter Connection off Circuit
Fig.8 Off-Circuit Connection of Ohm Meter
With circuits that are not equipped with a switch as shown in Fig.8, remove the particular component that you are interested in measuring resistance in order to isolate it completely from the circuit, this way only the resistance value of the specific component from the circuit will be measured by the meter, as compared to when measuring resistance of the target component while it is connected in the circuit which can result in measuring additional stray resistance values coming from other components included in the circuit, which will yield inaccurate resistance measurement result.

Measuring Circuit Continuity

Measuring continuity in a circuit is an electrical diagnostic procedure intended to verify the presence of complete electrical flow path in the circuit. In most electrical system, a blown fuse or a broken wiring connection will result in absence of circuit continuity which will show high or infinite resistance reading from the meter. Continuity reading using analog meter is done by selecting the lowest resistance function set at Ω x1 range and obtain a 0Ω reading from the meter.

Once again, similar to the procedure of measuring resistance, it is necessary that calibration is first performed before connecting an analog meter to the circuit. To do this, set the meter to the Ω x1 function range to prepare it for continuity reading. Short the tips of both the red and black test probes together then adjust the 0Ω adjuster knob until the pointer on the dial gauge is aligned to 0Ω on the scale.

Digital meters does not require calibration for continuity or resistance functions, but it does feature a special audible beeping sound function for quick continuity check. This additional feature incorporated in almost all digital meters allows the user to conveniently determine the presence of complete circuit by hearing the beep sound emanating from the digital meter without the distraction of having to glance back and forth at the meter while pointing the test probes to various test point locations of the electrical components in the circuit.

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