The voltmeter is an essential instrument used for measuring voltage. It offers stable performance, high accuracy, easy maintenance, and reliable operation, making it a popular choice in various electrical applications. To ensure accurate readings and safe usage, users must follow the correct procedures when using the device. Below is a detailed guide on how to properly use a voltmeter.
**How to Use a Voltmeter**
**1. Connection Method of the Voltmeter**
- First, check if the needle is pointing to the “zero†mark. If not, adjust the zero adjustment knob to set the pointer to zero.
- The voltmeter should always be connected in **parallel** with the circuit or device under test.
- **Note**: If the voltmeter is mistakenly connected in series, it will display the power supply voltage, and the connected bulb will not light up.
- A voltmeter can also be directly connected across the two terminals of a power supply to measure its voltage.
- Ensure that current flows into the **positive terminal** (red lead) and out through the **negative terminal** (black lead).
- **Note**: Reversing the polarity will cause the needle to move in the opposite direction.
- Select the appropriate range based on the expected voltage.
- **Note**:
- If you are unsure about the voltage level, estimate it first and choose a suitable range.
- If you cannot estimate, use the **test method** to determine the correct range.
- Start with the 0–15V range. Briefly close and open the switch. If the needle exceeds the scale, switch to a higher range.
- If the needle doesn’t exceed the scale but shows more than 3V, use the 0–15V range.
- If the reading is less than 3V, use the 0–3V range.
**2. Reading the Voltmeter**
- Determine the selected range of the voltmeter.
- Observe the scale value:
- For 0–3V range, each division is 0.1V.
- For 0–15V range, each division is 0.5V.
- Read the value by noting the number of divisions the needle has moved.
- **Note**:
- For 0–3V range: Voltage = 0.1V × number of divisions.
- For 0–15V range: Voltage = 0.5V × number of divisions.
- Remember that the reading on a larger range is five times that of a smaller range at the same scale line.
**Diagram of Digital Voltmeter Usage**
A digital voltmeter typically has three or four terminals, including one negative terminal (black wire) and two or more positive terminals (red wires). When measuring voltage, connect the voltmeter in parallel across the circuit or component being tested. Ensure the correct polarity and select the appropriate range before starting the measurement.
For example, when testing a dry battery, the voltmeter will show a reading such as 1.570V. In a parallel connection setup, the displayed value remains consistent, while in a series configuration, the total voltage equals the sum of the individual voltages.
When using an analog voltmeter, pay attention to the dial markings. At the 15V range, each large division represents 5V, and each small division is 0.5V. At the 3V range, each large division is 1V, and each small division is 0.1V. Accurate readings depend on identifying the correct number of divisions the needle has passed.
**Things to Watch Out For**
Always connect the voltmeter in parallel with the circuit. Double-check the polarity of the leads to avoid incorrect readings or damage. Choose the right range to prevent overloading the meter. Never connect the voltmeter in series unless it's a special case. These precautions help ensure both safety and accurate measurements.
By following these steps, you can effectively use a voltmeter in both digital and analog forms, whether for simple household tasks or more complex electrical experiments.
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