TLE 7 - LO2 carry out measurements and calculations

Learning Outcome 2

Carry out measurements and calculations

PERFORMANCE STANDARDS

Appropriate measuring instruments are selected to achieve required outcome.
Accurate measurements are obtained for job specifications.
Calculations needed to complete work task are performed using four fundamental operations.
Instruments are read to the limit accuracy of the tool.

What Do You Already Know?

Let us determine how much you already know about carrying out measurement and calculation. Take this test.

What Do You Need To Know?

Read Information Sheet 2.1 very well then find out how much you can remember and how much you learned by doing Self-check.

Information Sheet 2.1

Resistor color coded value is not absolute. The real resistance of the resistor is sometimes lower or higher than its color coded value but not to exceed its tolerance level. Tolerance is the limit on how far the real value of the resistor can deviate from its color coded value. It can be more or less but subjected to a tolerable limit. In the color coding chart there is a column for tolerance. Color gold is + or – 5%, silver is + or – 10 %, and the no color means + or – 20%.

Procedure in interpreting the tolerance of resistor

1. Identify the tolerance color of the resistor being analyzed. Assuming the color is gold which has a value of + or – 5%.

2. Convert the percentage into its decimal equivalent. 5% is equivalent to .05

3. Compute for the percentage of the color coded value. Assuming that the color coded value is 100 ohms ± 5%.

So 100 x .05 = 5

4. For the + side, add 5 to the color coded value of 100.

100 + 5= 105 ohms

That is the maximum deviation for that resistor. Beyond that, the resistor will not be fitted for the circuit which requires such tolerance.

5. For the – side, deduct 5 from the color coded value of 100.

100 – 5 = 95 ohms

That will be the minimum deviation for that particular resistor. Far beyond that the resistor will be considered to be defective.

6. Finally the value of the resistor with colors brown- black- brown – gold is 100 ohms with a deviation of +5 or -5. (95 ohms -105 ohms)

How Do You Apply What You Have Learned?

Show that you learned something by doing this activity

Operation Sheet 2.1

Objective: To compute for the tolerance ceiling of carbon resistors.

Materials:

20 pcs. Carbon resistors
Paper and pencil

Procedure:

1. Arrange resistors as done in the first operation.

2. Identify the tolerance color and record them in the resistor tabulation sheet.

3. Compute for the maximum value of the + tolerance.

4. Compute for the maximum value of the – tolerance.

RESISTOR TABULATION SHEET

How Well Did You Perform?

Find out by accomplishing the Scoring Rubric honestly and sincerely. Remember it is your learning at stake!

Find out by accomplishing the Scoring Rubrics honestly and

sincerely. Remember it is your learning at stake

With perfect score of 10 ………………………….. 5

With 1 mistake …………………………………. .. 4

With 2 – 3 mistakes…………………………………3

With 4 – 5 mistakes ……………………………….. 2

With more than 5 mistakes ………………………. 1

Information Sheet 2.2

Resistor color coding gives us the color coded value of a given resistor as well as the maximum and minimum value as dictated by the tolerance but the actual resistance is still unknown to us. The actual value of the resistor and the recorded data will confirm the status of the resistor whether good or defective.

OHMMETER

Ohmmeter is a measuring instrument used to determine the resistance of a component or equipment. This instrument is a great help in knowing the actual resistance of the resistors we use in the two operation sheets.

The commonly used ohmmeter in electro-electrical laboratories now nowadays is embedded in a multi-function testing instrument called the (Volt-Ohm-Milliammeter ) VOM. For this discussion the VOM will be used but confined only to the ohmmeter section.

A. PARTS OF A MULTI TESTER

Ohmmeter Scale- Nonlinear scale where reading of the resistance is based. It is usually found in the uppermost part of the VOM.
RANGE SELECTOR KNOB (Selector switch) makes it possible to select different functions and range of the meter.
POINTER - The needle-shaped rod that moves over the scale of a meter. It is mechanically connected to the moving coil.
Adjustment screw - makes it possible to adjust the pointer to the zero position of the scale.
SCALE is a series of marking used for reading the value of a quantity.
Test probe positive (red), negative (black) - used to connect the circuit to the electrical components being tested.
Zero-ohm adjusting Knob is used to zero-in the pointer before measuring resistance.

Analog Multimeter Labeling Activity

Digital Multimeter Labeling Activity

PROCEDURE ON HOW TO INTERPRET RESISTANCE READING IN AN OHMMETER

1. Know the value of individual calibration in the ohmmeter scale.

An ohmmeter scale is nonlinear which means the value of one line or calibration may not be true to other lines. It is therefore proper to assign values to every line for proper and accurate interpretation

As shown in the illustration, the scale can be divided into eight areas where individual treatment has to be made. Several mathematical computations will be involved to show the manner how values of individual lines are resolved.

2. Identify the appropriate range multiplier to be used Range multiplier is from R X 1, R X 10, R X 100, R X 1K, and R X 10K.

3. Connect the metallic part of the test probes and take note if the pointer points at zero. If not, adjust the zero ohm adjustment to zero.

4. Make the necessary resistance measurements.