Types of Errors in Physical Measurement

Measurement is the activity of taking the value of the object being measured. In the measurement process, mistakes are often made. Due to the factors that cause errors, it can be ascertained that the measurement may not be 100% accurate. This article will discuss the various types of errors in measurement. Framed to fit curriculum 13 with text that is light and easy to understand. because we are just ordinary people who cannot escape mistakes and only God is perfect, then every measurement process must have errors. Either from the object being measured, the tools are invalid and damaged and the error on the practitioner/observer when carrying out the measurement process.

This article is partly based on the BSE book and partly based on the author's learning experience. If we take measurements it is impossible to produce a 100% accurate value. But there is always uncertainty in the measurement process. Try measuring objects in the environment around you. For example, measure your pen using a ruler. What is the result? Are your pencil length measurements 100% accurate? There must be uncertainty that the ruler only has an accuracy of 1 mm and the object being measured maybe 0.00001 mm longer or shorter. 

This causes uncertainty in the measurement. This is common in physics because we as God's creatures are imperfect and often make mistakes. My lecturer once said that physics is a definite science whose certainty cannot be ascertained, why is that because everything in the universe is all relative, nothing is absolute except God, even time, which is one of the basic quantities, can expand or shrink. quoted from isanggar. Uncertainty in measurement is generally caused by systematic errors and random errors. We discuss these errors one by one as follows:

A. Common Errors.

General error is an error caused by limitations on the observer when carrying out the measurement process. Common mistakes are usually when doing the measurement process on a small scale like you do when measuring. Low accuracy in observations causes errors in measurement. And also the lack of skill in using tools also causes errors in measurement.

B. Systematic Error.

Systematic error is an error that occurs because it is caused by the tools used or the influence of the surrounding environment. For example calibration errors, errors at the zero point, parallax errors, changes in temperature, and environmental inertia. We will discuss the following:

1. Calibration Error.

Calibration errors occur because the value of the tool or the standardization of the tool is not right. This causes the measurement measured by the measuring instrument to be larger or smaller than the actual value. The cause of this calibration error is a common error, namely the lack of accuracy of the tool user in calibrating the measuring instrument. The way to overcome this calibration error is to calibrate or re-standardize the measuring instrument using standardized measuring instruments.

2. Zero Point Error.

The zero-point error occurs because the zero point on the scale of the tool used is not right on the tool that coincides with the pointer or the value on the measuring instrument does not return to zero. This causes an increase or decrease in the value corresponding to the difference in the true zero scales of the tool's pointer. The way to overcome this zero-point error is to make corrections to the measurement results that are known to have zero point errors. For example, if the needle is not right on the zero scales, i.e. the scale needle on the tool points to the number 0.2 on the unit scale, then when writing the numbers from the measurement, to get the actual results is to reduce the 0.2 unit scale so that the results obtained can be correct. .

3. Tool Component Error.

This tool component error occurs because there is damage to the tool. Damage to the tool components can clearly affect the reading of the measuring instrument. For example, if the ampere meter component is damaged, such as a rusted cable causing the resistance to the cable to increase. This causes the flow of electric current to be not optimal and the scale in the ammeter measurement is smaller than the actual one. On the spring balance, if the spring used is old and worn, it will affect the spring constant. This results in the needle or pointer being incorrect at zero, resulting in an incorrect value. This error can be overcome by repairing/servicing the components of the measuring instrument or by replacing the component or measuring instrument with a new one.

4. Parallax Error.

Parallax error occurs when there is a distance between the needle and the scale lines and the position of the observer's eye is not perpendicular to the needle. This causes errors in measurement because the needle and the scale line do not match what the observer sees in determining the value of the measurement results.

C. Random Error.

Random errors occur due to subtle fluctuations during the measurement. This error occurs due to the motion of the molecular in the air, fluctuations in electrical voltage, the ground vibrating noise, and radiation. It can be explained as follows:

a.Born's Motion in the Air.

Bowen's motion in air is a continuous molecule-molecule motion that occurs in the air continuously. The motion of the molecules is irregular. This motion can undergo very fast fluctuations that can cause the needle to be disturbed by collisions with molecules in the air.

b. Electric Voltage Fluctuations.

The voltage of the power plant or power generating equipment such as batteries, batteries, voltaic elements, and so on. Always experiencing small irregular changes and very fast resulting in inconsistent electrical measurement data. Such as measuring electric voltage using an ampere meter or voltmeter.

c) Vibrating anvil.

Vibrating anvils can also affect measurements, and result in measurement errors, especially in very sensitive measuring instruments such as earthquake measuring instruments (seismographs). A seismograph is an earthquake measuring instrument that requires a very stable base if the base is unstable. The anvil will vibrate and will affect the measurement of the instrument.

d.Noise

Is one of the causes of random errors. Noise can be found in electronic objects. This disturbance can be in the form of rapid fluctuations in voltage due to temperature changes in the tool components.

e.Background Radiation

f. Radiation of electromagnetic waves from space (cosmos) can interfere with the reading and operation of measuring instruments. For example, electromagnetic wave radiation from cell phone signals causes interference with aircraft measuring instruments. Therefore, mobile phones should not be turned on while in an airplane.

Measurement uncertainty seen from the way it is done is divided into 2, namely:

Uncertainty on a single measurement.

A single measurement is a measurement that is carried out only once. The value of the measurement results is considered correct. While the uncertainty is obtained from half the smallest value of the instrument on the measuring instrument. For example, on a measuring tool for length, namely a ruler. This measuring instrument has an accuracy of 1 mm, so by applying a single uncertainty, x = 1 mm x 1/2 = 0.5 mm = 0.05 cm because the uncertainty has two decimal places, the uncertainty must use two decimal values ​​and the measurement results of the object by

The ruler is 12 cm. So that the length of the final object is the same as the measurement using a ruler, which is 12 cm plus or minus the uncertainty value, which is 0.05 cm.

L= Xo ± x

= 12 cm ± 0.05 cm

Then the length of the measurement results is 12.05 cm or 11.95 cm

Uncertainty in Repeated Measurement

Repeated measurements are carried out so that we get more accurate results in the measurement process. So how do you report repeated measurements? On repeated measurements, you get as many reports as N times. Based on Statistical Analysis, the best value to replace the correct value is the value of X0. while the symbol of certainty is x. The formula for repeated measurements is obtained as follows:

In a single measurement, the value of uncertainty is called the absolute uncertainty value. Less absolute uncertainty in a single measurement. The single measurement is getting closer and closer to the truth. How do you determine the number of numbers in determining repeated measurements? The way to determine the number of numbers in repeated measurements is to find the relative uncertainty. Relative uncertainty can be determined by dividing the measurement uncertainty by the average value of the measurement. Systematically it can be written as follows.

After knowing the relative uncertainty you can use the rules agreed upon by scientists to find out how many numbers can be reported in measurement such as relative uncertainty 10% is entitled to two numbers, 1% is three digits is 0.1% is entitled to four numbers