Write a summary and fill out the worksheet for this lab . The link for the worksheet is already given on the worksheet and canvas . make sure to watch all the youtubes which I am posting below.
Operation of a Digital Multimeter
1. Terminals The terminals are where you connect the lead wires for measurement. The lead wire's red color represents the (+) pole, and the black color represents the (-) pole. The image below shows two common variations of the terminal inputs for a digital multimeter.
COM : It means a common ground terminal. Connect the black lead wire here.
10A : It is used to measure the current in the range of 0 to 10A. Connect the red lead wire here for large currents.
V•? : Used to measure voltage and resistance. Connect the red lead wire here.
V?mA : You can measure voltage, resistance, and current in milliamps (mA); small currents only! Connect the red lead wire here.
- [Image unavailable: Multimeter electrical terminals]
- 2. Voltage Measurement
- Since DC voltage (DCV) and AC voltage (ACV) have different measurement mechanisms, it is necessary to turn the rotary switch dial to the appropriate voltage type.
- V- : DC voltage measurement (Location 4)
V~ : AC voltage measurement (Location 5)
[Image unavailable: AC-DC multimeter dial]
In this part of our exercise you will practice measuring the DC voltage of two common batteries. You will also measure the AC voltage of several different power receptacles used in various countries around the world. Knowledge of AC voltage requirements in different parts of the world is required for the successful operation of electronic devices internationally. You will record your values in Table 1 and Table 2 of your lab worksheet respectively. The procedure is described in Table 1 and Table 2 of your lab worksheet.
3. Resistance Measurement
The resistance can be measured by turning the rotary switch to the '?' zone. The resistance value is measured by touching the lead wires to the opposite ends of the resistance.
- When measuring resistance, pay attention to the range. For example, if you measure a small value resistance in a large range, the measurement result will be '0' since it will be too small to register. Conversely, infinity (a '1' in the left corner) is displayed when the multimeter's measuring range is exceeded. Therefore, it is better to choose a range slightly larger than the expected resistance value. For example, if you measure a 10? resistance, it is appropriate to put the rotary switch range at 200. If the value is initially unknown then its best to start high and rotate the dial to a lower range until you get a reading in the display.
- Resistances in the form of resistors are either identified with a labeled value or more commonly with a color band code that all technicians should learn to read. There are 3 to 6 color bands that give the resistance depending on how precise the resistor value needs to be. When there are 4 or more bands, the last band gives the tolerance or the plus or minus percentage range over with the value can vary. The more bands, the greater the accuracy of the resistor value. Most common resistors have a 5 or 10% accuracy (displaying a gold or silver color band at one end). The typical common 4 band resistors that we will examine have the following color code described in the video and summarized in the figure below.
Resistor Color Codes - 4 band resistors[Image unavailable: Color Code Table for 4 band resistors]
As an example, a resistor with a brown, black, red then a gold band would have a value = 10 x 100 = 1000 ohms ± 5%. This means that it could have an actual value that could vary from 950 ohms to 1050 ohms.
In this exercise you will calculate the value of a number of 4 band resistors and use our multimeter to verify those values. You with record your values in Table 3.
4. Current Measurement
Current is a physical quantity different from voltage and refers to the amount of electric charge flowing through the wire per hour (or second for example). Therefore, to measure the current, you must "cut the wire" to be measured. In practice that means that you must insert the multimeter directly in the current flow path to measure the current. Some devices measure without "cutting the wire" using magnetic induction that we will learn about later in the course.
There is one thing to be aware of when measuring current. During the current measurement, the resistance inside the multimeter becomes almost '0'. This is because the multimeter must not interfere with the flow of current. When conducting current measurements you must be careful because the voltage source may cause overcurrent (too high a current) to flow and damage the multimeter. Some high-end multimeters have a protection circuit. Most have at least a protective fuse internal to the meter.
You must have a complete electrical circuit for current to flow. In other words the current must flow through a load where it does work and be able to return to its source. We will use a simple resistor to represent a load. The current from a battery will flow through the resistor and the multimeter and back to the battery. The voltage, current and resistance behave according to Ohm's Law where I = V/R or 1 amp = (1 volt)/(1 ohm). To find the current divide the applied voltage by the resistance through which the current flows. Compare this to the value measured by the multimeter. Note that the multimeter must be directly in series with the flowing current to measure correctly.
[Image unavailable: Current measurement setup]
In this exercise you will determine the value of the resistor and calculate the current using Ohm's Law. You will adjust the multimeter dial to a current setting that is about the same range as the value that you calculated. You will then verify those values using the multimeter by recording the value or the current in the display. You will then record your values in Table 4 as instructed in the lab worksheet.
We will make use of a simulated multimeter using the link below to make the voltage, resistance and current measurements noted above. We will go over the details during our lab session.
You will record your values in the worksheet provided for this exercise. How to use a multimeter is given on canvas make sure to watch that . I have uploaded the worksheet below .