Lesson 1: Measuring Tools and Instruments

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Overview

This lesson covers the knowledge, skills and proper attitude on identifying electrical measuring tools, appropriate and proper use of measuring tools and instruments, and reading of Multitester.

Learning Objectives

At the end of this lesson, you should be able to:

Cognitive Domain

Identify measuring tools and instruments used in electrical works.

Affective Domain

Practice proper use of the measuring tools and instruments.

Psychomotor Domain

Perform appropriate and proper use of measuring tools and instruments and reading of Multitester.

Watch the videos below and perform activities given!

Now, it’s time for you to apply what have you’ve learned!

Learning Activity 1

Instruction: Answer the following questions that are given on the document provided and submit your answer through Google Drive Link below.

The File Name of your output shall always be in this suggested format:

SurnameFNMI_LearningActivityNo.

Example: DelaCruzJP_LA1

Submit or upload your output to the Google Drive Link. Click the button below:

Learning Activity 1

Module 3 Lesson 1 Activity Sheet.pdf

Learning Activity 2

Answer the given questions below! Reminder: Always Read and Analyze directions.

Click here: https://forms.gle/SJRyJiN6gsYAL2de7

It's now time to explore and learn more!

Read the information given below.

Multitester

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. Multimeters may use analog or digital circuits—analog multimeters and digital multimeters (often abbreviated DMM or DVOM). Analog instruments are usually based on a microammeter whose pointer moves over a scale calibration for all the different measurements that can be made; digital instruments usually display digits, but may display a bar of a length proportional to the quantity measured.

A multimeter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems.

Different Parts of Multitester

This electronic measuring tool needs a number of components to be able to perform the tasks for which it was designed to work well. So, the result of the cooperation between these parts is measuring the values we have already mentioned. The parts of a multitester are a scale, a needle or pointer, an adjustment screw, a zero-ohm selector, a range selector knob, some ports and test probes.

In the following, we will read more about each of these components, their roles and how they work.

Scale: This is how you read the value being measured. For an analog multitester, this is a series of markings in a semicircle. Depending on the complexity of your multimeter, you can read different variations such as voltage, current, and resistance on the device screen and scale section. Which value you are measuring depends on what port you plugged into on your analog multitester.

Needle Pointer: This is the needle-shaped rod that moves over the scale of a meter. The needle pointer is mechanically connected to the moving coil. The value the pointer hovers over indicates the value being measured by the multitester. Note that when there are multiple values being measured on the same scale, you’ll need to pay attention to which port the multitester is connected to. Match the port up with the value being measured.

Adjustment Screw: This part which is also known as the dial or infinity knobs allow you to adjust the pointer to the zero position of the scale. This is usually accompanied with the help of a flat head screwdriver. It is good to know that the name ‘infinity knob’ comes from the fact that at 0 voltages, you have ‘infinite resistance’.

Zero-Ohm Adjustment Knob: The zero-ohm adjustment knob is used to calibrate the multitester when you want to measure the resistance of an object. To make sure the multitester is calibrated correctly you have to turn on the multitester, then connect the metal tips of the two probes and finally use the zero-ohm adjustment knob to adjust the needle to point to ‘0 ohms’ on the scale.

Range Selector Knob: This part is also known as a selector switch. A range selector knob allows you to adjust the settings of the multitester (range selector knobs are also present on the best insulation resistance testers). Using this you can change what the multitester is measuring (e.g. voltage, current, or resistance), as well as the range of the measurement (e.g. volts or millivolts). The range selector knob can be auto ranging, or manual ranging.

Auto ranging is much easier to work with. You simply adjust the dial to the symbol corresponding the electrical parameter you want to measure. You connect the test probes and you have your measurement.
Manual ranging, on the other hand, is a little bit trickier. With manual ranging, you need adjust the dial so that the value it is set to is higher than the maximum value you expect from your circuit

Ports: The holes at the front of the multimeter are known as ports. You need to plug your test probes into the appropriate ports to allow the multimeter to measure the parameter that you’re interested in.

Test Probes: A test probe or a test lead is an instrument used to connect a multimeter to a Device Under Test which is known as DUT. Test probes are flexible, insulated wires. They are able to establish an electrical connection between a multimeter and the DUT without exposing electrical workers to live conductive parts. Red test probes connect to the positive terminal, and black test probes connect to the negative terminal.

Proper care and maintenance of Multitester

Read manual of instructions on how to operate the multi-tester.
In reading the amount of voltage, always start with the highest range to avoid reading voltage higher than the tester setting.
Be sure that the tester is set to the correct range setting: resistance range when measuring the ohm, voltage range when measuring voltage and ammeter range when measuring the value of electric current.
Always check the condition of its battery. Worn out batteries will damage the internal setting of the tester.
When the tester is not in used or will be stored, set the selector switch to 1000V or to OFF position.
Never drop the tester.

To read the resistance range of the multi-tester, the given table below will be used. The unit of measurement to be used to determine its resistance is ohm.

How to Use and Read a Multitester to Measure Voltage

Follow these steps to measure voltage with your multimeter.

1. Identify whether the voltage you’re measuring is AC or DC. If you are measuring voltage in your home, it’s probably AC. If it’s in your car or in a battery-powered device, it’s probably DC.

2. Turn the selection switch to the appropriate voltage. AC voltage has a symbol that looks like a sine wave, which is the universal symbol for AC. The symbol for DC is a solid line with a dashed line below it.

3. Plug the black probe into the COM outlet found on the multimeter.

4. Plug the red probe into the jack, marked with a V.

5. Turn your selector switch to the highest setting in the proper voltage category. Remember that mV stands for thousandths of a volt, so this is a very low setting.

6. If you’re testing AC voltage, you should be wearing safety gloves. Gloves are always a good idea when working with electricity.

7. Power up the receptacle or component for which you are testing voltage by either closing the breaker in your breaker box, turning the ignition in your car, or turning on the battery-powered device.

8. Touch the black probe to the terminal on one side of the component you’re measuring, and the red probe to the terminal on the other side of the component.

9. If you’re not getting a clear reading, turn the selector to the next highest setting until you have a recordable number.

Take note of these additional and important safety precautions before testing voltage.

Make sure your probes are not damaged and that there are no exposed points in the test wires.
Double-check that the red probe is plugged into the V outlet on your multimeter. Plugging into the wrong jack will dangerously damage your multimeter.
Always start at the highest voltage range on your multimeter selection switch.
If your multimeter probes have clips, this provides additional safety. You can clip the probes to the circuit before powering up the device or turning on the breaker.

How to Use and Read a Multitester to Measure Current

Here are the steps you take to measure current with your multimeter:

1. Turn off the power to the circuit that you’ll be measuring.

2. Turn the selector dial to A which is current.

3. Plug the black probe jack into the COM outlet on your multimeter.

4. Plug the red probe jack in the appropriate current outlet, either the high current (A) or the low current (mA or µA).

Warning: If your measured current is higher than the low current limit, you can blow a fuse in your multimeter if you accidentally use that outlet.

OK let’s get real. Unless you are measuring a flame rod or thermocouple you very likely will not need to find thousandths or (good grief!) millionths of amps. So just stick the red probe in the A jack

Now, this is where it gets messy. If you have a clamping meter, just skip all this and jump to the section on how to measure current with a clamp meter.

5. If you’re still reading, here’s what you need to do. The ammeter must be placed in series with the circuit to measure current. So the wire feeding the circuit must be opened and the meter probes placed across the gap. For example, if you want to measure the current in a circuit with an outlet receptacle, you could

a) Remove the live wire from the plug

b) Place the red lead from your meter on the disconnected wire

c) Place the black lead on the plug terminal where the live wire was before

d) Make sure you’re not touching either of the exposed parts of those leads

e) Turn the power back on

Now your meter is part of the circuit and is counting amps as they fly by.

Reminder: make very sure your meter is on the amps setting before doing this.

How to Use and Read a Multitester to Measure Resistance

Since ohms are units of resistance, we begin by setting the dial to ohms to measure resistance.

Follow these steps to measure resistance with your multimeter:

Note: Some of these steps are specific to manual ranging maters. If yours is auto-ranging – you can ignore steps #3-5.

1. Turn off the power!

2. Turn the selection switch to resistance, or ohms (Ω).

3. Insert the probes into the proper jacks. The black probe will go into the third jack, labeled “COM.” The red probe plugs into the fourth jack.

4. If the multimeter has an on/off switch (other than the selection switch), turn it on. Make sure the display activates.

5. Set the selection switch to the highest resistance range to start your measurement.

6. Touch the probe tips to the wires on opposite sides of the fuse or item for which you’re measuring the resistance. Resistance measurements will always be measured Your meter will measure the resistance it “sees” between the 2 probes. For example, If your probes are on either end of a fuse then it will measure the resistance of the fuse.

7. If the display reads zeroes or a very low decimal, then adjust the selection switch to the next highest range until you see more numbers in the reading. This will give you a more accurate reading.

8. After you have recorded your reading, turn off the multimeter to preserve the batteries.

9. Finally, turn the selection switch back to the highest resistance units. This is for the protection of the multimeter, in case your next measurement requires greater current.

This is also a great way to prove a wire has continuity or is unbroken between two points.

If you were to measure resistance from one end of a wire to another, and if that wire is unbroken, what would you expect the meter to indicate? High or low resistance? It would be low since the wire is continuous. You would read zero or a small fraction of 1. If on the other hand, there is a break somewhere along the line, what would you read? It would be infinite resistance or OL which means overload.

Here are some additional tips to make sure you are taking a correct resistance measurement:

The component you’re measuring should be removed from the circuit or appliance, to make sure you don’t accidentally measure the resistance through a different pathway.
The component you measure should also be disconnected from any batteries or external power source. The multimeter batteries will provide the necessary power to test the resistance.
If you’re testing a capacitor, make sure it’s discharged in order to prevent electrical discharge into your multimeter.
Capacitors may take a moment to stabilize when you apply the multimeter probes. This is because the probes can actually charge the capacitor slightly.
If you are testing the resistance of a diode, and you can’t get a reading, then switch the probes on the diode terminals. Diodes only conduct current in one direction, so if your probes are on the wrong terminals, you will either get a zero reading or an unreasonably high resistance reading.
If you are measuring particularly high resistance and your fingers are in contact with the terminals, it’s possible that your fingers will affect the resistance reading. Just make sure you are not touching the metal part of the probes.

How to Use and Read a Multitester to Calculate Power

A multimeter does not directly measure power or watts.

Instead, an appliance’s watts can be calculated rather simply by measuring the voltage and the current, and then multiplying them together.

Here are the 2 simple steps to determine watts:

1. Carefully follow the steps above to measure voltage and current.

2. When you have measured both values, multiply them together.

Other Measuring Tools and Instruments

Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature, etc., to a unit of measurement, such as the meter, second or degree Celsius. The science of measurement is called metrology. The English word measurement originates from the Latin mēnsūra and the verbmetiri through the Middle French mesure.

Test Light

A pocket size tool used to test the line wire or circuit if there is current in it.

Micrometer

Used to measure the diameter of wires/conductors in circular mils. It can measure small and big sizes of wires and cables.

Wire Gauge

Used in determining the size of wires/conductors. The gauge ranges from 0 to 60 AWG (American wire gauge)

Ruler/Foot Rule

A measuring tool used to measure length, width and thickness of short flat object and in sketching straight lines.

Pull-push Rule

A measuring tool used to measure the length of an object in centimeter and inches.

Ammeter

An instrument used to measure the amount of electrical current intensity in a circuit. The unit of measure is ampere (a). It is connected along or series to the circuit.

Voltmeter

An instrument used to measure electrical pressure or voltage of a circuit. The unit of measure is volt (v). This is connected across or parallel to the circuit.