IDEAL INDUSTRIES INC. The Basics of Digital Multimeters A guide to help you understand the basic Features and Functions of a Digital Multimeter.
The Basics of Electricity To better understand digital multimeters, it’s helpful to become clear on the basics of electricity. After all, DMMs always measure some aspect of electricity. Electricity passing through a conductor is similar to water flowing through a pipe. Every pipe has force that creates a certain pressure, causing water to flow. In the case of electricity, that force might be a generator, battery, solar panel or some other power supply.
Unlike alternating voltage, direct voltage is a steady flow of positive energy. It is commonly stored in batteries for use in electronic equipment. Current is the flow of electricity through a conductor. As with voltage, there are two types of current, AC and DC. The symbol for current is the letter A. The third component is resistance, measured in Ohms. Resistance in the circuit impedes the flow of current through a conductor.
Electrical Circuits In an Electrical system, there are two ways that loads are connected in a circuit, in Series or in Parallel. In a Series Circuit, each device is connected together in a line. Current flows through each device connected to the circuit. If you were to increase the resistor in the Series Circuit shown below, the light would dim. You have restricted the flow or available current to the light.
Types of Multimeters There are two common types of Multimeters, Analog and Digital. Digital Multimeters (DMMs) are the most common. They use a liquid crystal display (LCD) technology to give more accurate readings. Other advantages include higher input impedances, which will not load down sensitive circuits, and input protection. Analog meters use a needle movement and calibrated scale to indicate values. These were popular for years, but recently their numbers have declined.
meters meet some safety standard such as UL601010 or IEC (International Electrotechnical Commission). DMMs at a Glance The port panel is where you plug in your test leads. The diagram below explains where the test leads go for specific tests. Digital multimeters are more commonly used because of a few key features, including higher accuracies, higher input impedances and input protection.
For additional information on Meter Safety refer to the IDEAL whitepaper on METER SAFETY The Dial Setting the Function The dial of the DMM allows you to choose the function you’re interested in measuring. Whether you intend to measure one of the three elements of Ohm’s Law, or a more advanced function like frequency or capacitance, you must first set the dial to the appropriate function.
For A complete listing See Appendix B Auto vs. Manual Ranging Tech note: Manual ranging multimeters force us to think about the measurement before we select the range of the meter. As an example, if I want to measure 120V AC on a manual ranging meter I would turn the Dial or switch to the VAC section and select the 200V Range. This gives you ample measurement range and the maximum resolution for the measurement.
count or floor and refers to the least significant digit of the display in reference to range and resolution. If we want to determine the maximum error of the meter that is measuring a source of 12V, first determine the percentage error and add the count or floor. The % accuracy for a 12V source would be 12 x 0.005= 0.06 To determine the count, we must determine the meter’s range and resolution. If the display is a 4000 count display, we need to determine the best range and resolution.
Range 600 400 40 4 400mV Reading 600 399.9 39.99 3.999 399.9 Resolution 1V .1V .01V .001V 0.1mV The 4000 count unit would be set on the 400V range to measure 280V, and have a maximum resolution of .1V In this case the 4000 count unit would give you the best resolution It is important that we understand our numerical expressions to properly setup or read the display of a Multimeter. In this example we have an auto ranging meter, measuring a 2,800,000 ohm resistor. The display reads 2.800 M Ω.
Instrument Input Jacks or Ports The input jacks or ports of your meter are the working ends of the instrument. Use care when connecting leads to your instrument. Pay close attention and be sure to connect the leads into the correct port that is marked for the measurement selected on the dial. DC Voltage Measurements: To measure DC voltage, we place the Red lead into the VΩ COM port. Turn the dial or switch to VDC or V If it is a manual ranging meter set it for the proper range.
Tech Note: Voltage Measurements Voltage measurements are perhaps the most common function used on a multimeter. Voltage is measured between two points so we must make sure that we have solid contact at each point. The proper way to connect a meter is to connect the low or ground (black lead) first and the High (Red lead) next. We remove the leads in reverse order, Red first and then Black. Whenever making live voltage measurements use the Three Point method.
In commercial and industrial environments, loads like electronic lighting, computers, variable speed drives and other electronic equipment draw current in short pulses. This type of load is called non-linear because it doesn’t draw its current linearly with the load voltage. The non-sinusoidal or distorted waveforms create harmonics. This distortion of the waveform can cause an average responding meter to be as much as 10% to 40% inaccurate.
To measure current with a multimeter, turn the power off at the breaker as close to the source as possible. Break the circuit, connect the multimeter in series with the circuit, and reestablish power. Tech Notes: Good multimeters are now protected by a high-energy fuse. High energy fusing is used to protect the meter and the user, but let’s not forget “Murphy’s Law”. The most common mistake is to accidentally have the test leads in the current input jacks and make a voltage or parallel measurement.
'Clamp-meters also allow a much higher level of current measurements. While most multimeters have a maximum internal current measurement of 10 amps, clamp meters are available that measure 400, 600 or even as much as 2000 amps. Meters with Clamp adapters can be used to make high current, but Clamp-meters are much simpler to use. DC current is measured through the use of a Hall Effect probe.
Resistance Measurements ). When you first place the meter in the ( ) function the meter will give a display of ―OL‖ or ―1____‖ indicating an infinite reading. It is important when measuring Resistance that the circuit be de-energized or turned off, or the circuit may damage the meter. Most meters have overload protection on all ranges to prevent this, but you should check the specifications of your digital multimeter to be sure. For resistance measurements, place the test leads on each side of the resistor.
Capacitance Measurement A capacitor is a device that stores energy. It is widely used to give a boost of energy at start up when power is applied to lighting and motor systems. To test a capacitor, first remove power from the device. Remember that a capacitor stores energy so the next step is to discharge the device. Now you are ready to test. Never test without verifying that the energy has been discharged from the capacitor.
Advanced Multimeter Functions Many features are available on today’s advanced digital multimeters to make measuring electrical systems and components easier. There are two common methods used for these advanced features. Direct Key Selection or Menu Selection. With the Direct Key function, ―press and hold‖ for one second will activate the feature. ―Press and hold‖ for two seconds will disable the function. Try this with the RANGE key on an Auto-ranging multimeter.
Min/Max or Min/Max/Avg. The min/max button captures the lowest, highest and average value that the meter has seen during the duration of the measurement. Digital multimeters with a dual display will show the real-time or instantaneous measurement on the main display, and show the min-max- or avg. value on the secondary display. Pressing the min/max button will step you through the minimum, maximum, and average readings recorded during the duration of the test.
been set as the reference value, all new measurements will be the resistance of the circuit or component without the test lead resistance. Peak Hold and Peak Min/Max Unlike True RMS measurements, which calculate the effective value of the voltage or current waveforms, Peak measurements capture the highest amplitude of the waveform. Peak hold is often used to measure in-rush current caused by a motor start-up.
Appendix A Ohms Law Pie Chart Direct Current calculation Symbolic V W Ω A C Hp EFF PF kW kWh VA kVa Term Voltage Watts Ohms Amperes Capacitance Horsepower Efficiency Power Factor Kilowatts Kilowatt hour Voltage Amperes Kilovolt-Amperes Symbolic E P R I Term Voltage Watts Resistance Amperes Real Power Apparent Power Direct Current Ohms Law.
Ohms Law Pie Chart Alternating Current calculation AC Single Phase calculations Amperes = Watts / (Voltage x Power Factor) Watts = Voltage x Amperes x Power Factor Voltage = Watts / Amperes Volt – Amp = Voltage x Amperes Power Factor = Watts / Volt-Amp HP = (V x A x Efficiency x PF) / 746 Efficiency = (746 x HP) / (V x A x PF) A= W/(V x PF) W=V x A x PF V= W / A VA = V x A PF= W / VA HP = (V x A x EFF x PF)/ 746 Eff= (746 x HP) / (V x A x PF) AC Three Phase Calculations Amperes = Watts / (1.
Appendix B Measurement Functions Symbols VAC VDC Measurement Functions AC Voltage DC Voltage Measures amount of AC Electrical Pressure Measures amount of DC Electrical Pressure Milli Volts .00V or 1/1000V Amperes Measures amount of electron flow mA Milli Amperes .001 or 1/1000A µA Micro Amperes .
Glossary A, ampere or amp — The basic unit of electric current. AC, alternating current — An electric signal in which the current and voltage vary in a repeating pattern over time; the most common type of voltage. analog meter — A mechanical measuring device using a needle moving across a graduated scale or dial. APO- Auto-Power — Off Automatically shuts down unit after a certain amount of time to preserve battery life.
min/max — Feature that allows a meter to capture and store the highest and lowest readings during a specific measurement. ohm — The basic unit of resistance, specified as equal to that of a conductor in which one amp of current is produced by one volt of potential across its terminals. OL, overload — Signal amplitudes or frequencies above the specified limits of the instrument; typically displayed as ―OL‖ on the display of a DMM.
