Welcome back, Troubleshooters! For the past few Troubleshooting Thursday posts, we have been discussing TPC’s systematic troubleshooting methodology to build a solid foundation for learning troubleshooting. It is now time to start looking into the multimeter and other tools used to execute this approach.
Previously we discussed the importance of a proper follow-up after troubleshooting an electrical circuit, as the last step of a systematic troubleshooting process. Today, we will discuss the tools used to identify where a malfunction is occurring in a circuit. Specifically, we are talking about meters.
WARNING: Testing electrical equipment can be hazardous. The electrical energy contained in many circuits can be enough to injure or kill. Make sure you follow all of your company’s safety precautions, rules, and procedures while troubleshooting.
Types of Meters
There are many types of test instruments used for troubleshooting. Some are specialized instruments, designed to measure various behaviours of specific equipment. There are other types of instruments, such as multimeters, that are more general in nature and can be used on most electrical equipment. A typical multimeter can measure AC and DC voltages, resistance and current.
- Voltmeter: A voltmeter is used to test the differences in voltage between two points.
- Ohmmeter: An ohmmeter is used to measure the resistance between two points in a circuit.
- Ammeter: An ammeter is an instrument for measuring the current flowing in a circuit in amperes.
- Multimeter: A multimeter can test voltage, resistance and current. It is an ohmmeter, voltmeter, and ammeter all in one.
General Meter Rules
Before you perform a test, you need to know what the meter should read if the circuit is operating normally. You should make your prediction based on a circuit diagram. If the reading is anything other than your predicted value, you know that this part of the circuit is being affected by the electrical fault.
You should always test the meter before using it to troubleshoot.
- For a voltmeter, test the meter on a known voltage source before using. Your meter should read the correct voltage.
- For an ohmmeter, touch the meter leads together. The display should read 0 ohms, or very close to 0. With the leads apart it should read OL (infinity).
Here are some dos and don’ts for using a meter.
- Become familiar with its features. Read the instruction manual before using.
- Be sure that it is safe to use and there is no obvious damage to the meter or the meter leads.
- Be sure the test leads are in the correct sockets, and the rotary switch is in the correct position for the desired measurement.
- Keep your fingers behind the finger guards on the test probes when making measurements.
- To avoid false readings which could lead to possible shock or personal injury, replace the battery as soon as the battery indicator appears.
- Never measure resistance in a circuit without the circuit locked out and verified dead.
- Never apply more than the rated voltage between any input jack and ground.
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