Digital Multimeters (DMM’s) Description:
Fluke 116
A digital multimeter is a general-purpose measuring instrument that measures resistance, current and voltage. The meters measure electric current in ampere, volt and ohm. At times you will see multimeters listed as DMMs which simply stands for “Digital Multimeter.” In simpler terms, a DMM is an electronic tape measure for making electrical measurements. They were originally invented in the early 1920’s as radio receivers and other vacuum tube electronic devices became more common. In today’s world, almost all of the electronic products used in our personal and professional lives are built or serviced using multimeters. This handy tool can be a hand-held device useful for basic fault finding and field service work, or it can be used as a bench instrument which can measure to a very high degree of accuracy. Their main function is to troubleshoot electrical problems in a wide array of industrial and household devices such as batteries, motor controls, appliances, power supplies and wiring systems. Digital multimeters have a higher rate of accuracy compared to analog multimeters. The accuracy can be .5% compared to 3-5% for analog meters. It is extremely important to use a quality digital multimeter such as the Fluke 116 HVAC Digital True RMS Multimeter when diagnosing electrical problems.
How to Use a Digital Multimeter:
To measure voltage using a multimeter, plug the probes into the correct jacks on the multimeter. Black is negative and the red will go into the Volt/OHM/Temp jack. Do not put the red into the A or mA. When measuring AC voltage, switch the multimeter rotary switch to the V (wavy line). The reading will display when the probes are touched to the appropriate outlet or wire. When measuring DC voltage, the rotary dial needs to be turned to the V with a solid and broken line over it. When testing low voltage systems (less than 3VDC) use the mV setting. The result will display when the probes are touched to the appropriate area. When measuring resistance, follow the same directions; however, turn the rotary switch to the Ohm sign. Keep in mind the resistor’s rated value can be different than the measured value of a resistor in a circuit. Test leads can add .1% to .2% of error when measuring resistance. Testing the leads can be accomplished by touching the probe tips together and reading the resistance of the leads.
Safety When Using Multimeters:
To prevent the possibility of electric shock or injuries, never measure an in-circuit current when the open-circuit potential to earth is greater than 1000V. If the fuse blows during this type of measurement, the meter can easily be damaged and you have an extremely high risk of injury. It is imperative to check the meter’s fuses prior to measuring current and never to place the probes parallel to any circuit or component. Always use the correct function, range and terminals for all measurements. Remember, no tool by itself can guarantee absolute safety. The combination of the right tool and safe work practices will give you maximum protection. Use the following guidelines to increase safety when using a digital multimeter:
* Work on de-energized circuits when possible, also being careful to use lock-out/tag-out procedures. Always assume the circuite is live.
* Use insulated tools, wear safety glasses or a face shield and insulated gloves.
* Wear flame resistant clothing, and stand on an insulated mat.
* When making measurements on live circuits, hook on the ground clip first, then make contact with the hot lead. Hang or rest the meter when possible versus holding it in your hands.
* Use the three point test method; test a known live circuit, then the target circuit and finally test the target circuit again. This technique double checks that the meter worked properly before and after the measurement.
How to Choose a Multimeter:
The first thing to consider when shopping for a new multimeter is to analyze the worst-case scenario of your job. This will help to determine the category your use or application fits into. You will want to choose a meter that has a rating for the highest category you could be working in. Next, look for a multimeter with a voltage rating for the category that applies. Choosing the right digital multimeter requires evaluation of your basic measurement needs and job requirements, and looking at special features/functions built into the different types. Keep in mind the importance of test leads. The test leads need to be certified to as high or higher of a voltage and category than the meter. Also, look for multimeters and test leads with double insulation, recessed input jacks and test leads with shrouded input connectors. The main factors to consider include:
* Your work environment; voltage level, types of equipment, measurements and applications
* Specialty features/functions; capacitance, non-contact voltage, min-max record, data logging, trending, low impedance mode, frequency and temperature.
* Resolution and Accuracy; 6,000, 20,000 or 50,000 count resolution
Technology is changing rapidly and as electrical and electronic circuitry continues to get more complex, accurate diagnostic tools like digital multimeters are more important than ever. With the wide selection of features, choosing the right meter for the job can be challenging. Always keep safety the number one priority when using and choosing your next multimeter.
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