In the industrial world, devices that turn electric power into mechanical power are commonplace. Some examples of these include pumps, motors, conveyors, robots, and more. Voltage signals are actually the ones controlling Oscilloscopes. But what are Voltage signals and how do we capture them? Here’s what you should know about an Oscilloscope.

An oscilloscope or scopes are an important tool for electrons. Waveforms can become visible thanks to these devices. And because of this, they are useful in looking for any problems in the electronics circuit. Its name draws origins from the name cathode-ray oscilloscope (CRO) when it was still used, as seen in the old televisions due to the high voltages it needed.

Oscilloscopes display in waveforms the voltage signals, which is a visual representation of the variations of voltage. Think of it this way, a waveform is like a ripple traveling along surface water. But in totality, the best way to see signal changes is through plotting. The vertical (Y) axis shows the voltage magnitude while the horizontal (X) axis shows time.

Some other information you can see in the graph of an oscilloscope include:

• Voltage signal shape when operating as intended
• Current signal shape when using a current clamp suitable for using on an oscilloscope
• Anomalies on the signal
• Amplitude modulation of an oscillating signal and any frequency variations
• Whether the signal has noise and the changes to the noise

As an item used in electronics test equipment, it helps give insight into circuit operations and is the key to finding many issues and resolving them. Most of the modern oscilloscopes are digital which allows for a more detailed and accurate signal measurement as well as fast calculations, data storage capabilities, and even automated analysis. Handheld digital oscilloscopes such as the one by Presidium, offer more advantages over the benchtop models such as it being battery operated, that it uses electrically isolated floating inputs. This is an advantage of added features that makes its usage easier and more accessible to many different workers.

Visit our website at  https://presidium.ph/product-category/products/fluke-industrial-group-tools/portable-oscilloscopes/ to know more about our oscilloscope products or contact us +63282515165 / +63282570795.

Clamp meters are an electrical test tool that incorporates a basic digital multimeter with a current sensor. Clamps measure current. On the other hand, Probes measure voltage. Having a hinged jaw can allow the technician to clamp the jaws around a cable, wire, and other points in an electrical system. It measures the current in the circuit without the risk of disconnecting it. Below their plastic moldings are hard jaws that contain ferrite iron. Clamp meters measure and monitor magnetic fields as it goes through a conductor.

Another name you can call clamp meters is clamp-on ammeters. Additionally, what other thing you might want to know is that they have three types of categories.

Current Transformer

What you must know is that a current transformer is a type of instrument that produces secondary alternate currents. Ultimately, this makes it proportional to the AC current in the primary. This is used when a current or voltage is too high to measure directly. The secondary current is used for measuring instruments or processing electrical equipment. This process generally needs isolation between primary and secondary circuits.

Hall Effect

Hall Effect clamp meters can measure both ac and dc current up to the kilohertz which is 1000 Hz range. Similar to current transformer types, Hall Effect clamp meters use rigid iron jaws. Basically, when you use iron jaws it can actually help your device concentrate on the magnetic field that encircles the conductor. Compared to current transformer clamp meters the jaws are not wrapped by copper wires. Instead, the magnetic field produced by the conductor is focused across one or more gaps in the core after the jaws are clamped around the conductor.

Flexible

Flexible clamp meters evolved in 1912. From simple solenoids came an advanced test tool ready to take over the industrial market. Compared to the Current Transformer and Hall Effect clamp meter, the flexible clamp meter does not have an iron core. Instead, a wound helix-shaped coil that reacts to a conductor’s magnetic field was used. The faster the change in amplitude, the more voltage generated by a coil. The integrator circuit in the measurement device transforms that output to a signal that’s proportional to the signal in the conductor.

While clamp meters have different types, they all have the same fundamental methodology when making measurements. On the contrary, you can actually pass a probe in the conductor. There are multiple ways on how you can achieve this. One is the most convenient since it can be through the hard jaw and into the clamp meter. Another is a flexible coil of clamp accessory. Ultimately, this will result in a sum of currents flowing through the conductor as measured by the meter.

Fluke offers a 323 clamp meter which is a good basic troubleshooting tool for commercial and residential electricians. It includes True RMS measurements, optimized ergonomics, and a large display for efficient troubleshooting. Trust it to help you confidently diagnose problems almost anywhere. Reach us through https://presidium.ph/product-category/products/fluke-industrial-group-tools/clamp-meters/  to know more about our clamp meter products.

Electricity is a powerful form of energy. Therefore, following electrical safety standards is highly important. It is a given fact that electricity in its entirety is dangerous when not respected.

Presidium will help build a proper multimeter to protect anyone against electrocution, arc explosion, and other unnecessary incidents. A well-built-multimeter will carry a Measurement Category III rating and third-party certification of an independent test lab.

However, don’t be complacent with your meter. Regularly rated meters are preferable to those that aren’t. If not rated, the consequences might be drastic. Another factor is not having proper certification. This automatically does not guarantee any protection for you and for the device. This will eventually lead to insulation breakdown or arc explosion.

Presidium is an authorized distributor of Fluke Tools.

Why Presidium carries out Fluke Industrial Group tools and Fluke Calibration is that it takes the process of measuring the performance of products very seriously. All Fluke’s test and measurement tools are of high quality in performance and in results. It has the ability to exceed the expectations and safety requirements of a Product Compliance Laboratory.

To be simplified by Mr. Thomas Smith, A Product Compliance Manager, “We put the tools through a variety of foreseeable use and misuse scenarios replicating the conditions we’ve learned from our customers and Once we know the tools demonstrate sufficient safety margin and robustness here, we can be confident in knowing they’ll provide a high level of protection in the real world.”

Fluke Products undergoes a series of performance and safety tests and is certified by a third party. All of the products go through is…

• Baked
• Frozen
• Dunked in water
• Choked by dust clouds
• Rattled with vibration
• Bashed on the floor
• Zapped with electricity repeatedly

The Fluke Product Compliance Laboratory

The Fluke Product Compliance Laboratory has different workstations. It’s a mix from jutting out from the ceiling, walls, and down to the center of a large bright room. Safety engineers’ experts who are testing protocols and safety standards push Fluke tools and instruments to their limit and even up to their breaking point. “We test at least one level beyond the standard. Additionally, our work in foreseeable misuse has led to the development of new standard requirements.” Smith, added.

Furthermore, Fluke actually takes advantage of a variety of tests. Design weaknesses and errors are inevitable and they can happen to a lot of devices. Therefore, the lab has designed special testing to spot these faults immediately. Basically, these tests will benefit users by providing and utilizing protection as much as possible to avoid the dangers of working with electrical systems.

Presidium PH Corporation is an authorized distributor of Fluke Industrial Group and Fluke Calibration products in the Philippines. Having said that Fluke Corporation is the world leader in the manufacture, distribution, and service of electronic test tools, biomedical equipment, and networking solutions. Fluke Product Compliance Laboratory is accredited through CSA to test and certify products for their certification mark. Test procedures are laid out in detail and adhered to rigorously. Once a product has passed the appropriate tests, documentation is sent on for approval and registration.

Testing for safety and reliability

Fluke works with all nationally recognized test labs (NRTLs) such as the: CSA (Canadian Standards Association). The Fluke Products are accredited through CSA to test and certify products for their certification mark. Meanwhile, test procedures are laid out to make certain that it adheres to the requirements. Then, when products have passed the tests, documentation will be sent for approval and registration.

Fluke is also in partnership with the UL (Underwriters Laboratories), TÜV (Technischer Überwachungs-Verein), and ETL/Intertek. On the other hand, we make sure that Fluke lab meets all national and international requirement standards for the safety of every user.

All high-quality test instruments should undergo similar testing. Let’s talk about the example approaches of Fluke testing:

Impulse test

The first test is the impulse test that simulates a transient on an electrical installation from nearby lightning strikes or other large electrical disturbances from the switchgear. To test it, a meter is placed in a chamber and injected with a pulse of thousands of volts of electricity. Meanwhile, this process is to verify whether the meter protection will break down, tear up, or arc over. For this testing, a special test machine is used to generate the high voltage transient and fault current as defined by international and national standards.

Multi-Functional overload test

A test instrument should also undergo an inspection to make sure that it is able to withstand accidental overloads associated with the various functions of the meter. Fluke does this by utilizing the multi-functional overload test. This test involves injecting a high percentage of energy voltage into non-voltage measurement functions, testing for a case in which an operator mistakenly sends voltage into a non-voltage meter function. This mostly occurs if the user leaves the leads in the amps input jacks and then accidentally connects the leads across a voltage source: they have just created a short through the test instrument.

Highly accelerated lifetime test (HALT)

To guarantee the lastingness and permanence of its tools, Fluke uses HALT. This test is a combination of using a high-frequency 6-axis vibration at more than 150 GRMS (root-mean-square acceleration) with extremely fast temperature swings to simulate a lifetime of wear and tear. The chamber has the capability of going from -100 °C (-148 °F) to 200 °C (392 °F) in minutes, testing the tool’s ability to withstand elevated and combined stresses.

Transport under rugged conditions

Another important test is to simulate meters. This is usually done in rugged and rough conditions, such as in off-road vehicles used by the military. To test this, engineers place the meter on a vibration table where it is shaken at over 3 GRMS for at least 30 minutes per axis, repeatedly. With Fluke tools, one test is never enough. This is why meters are tested in several conditions to account for all circumstances.

Other tests are:

• Anechoic chamber lab test – To withstand radiated electromagnetic interference without displaying erroneous readings, and do not emit disruptive radiation.
• Drop test – To withstand surprises of breaking even at the lowest temperature rating of the product.
• Electrical static discharge (ESD) – To withstand static electricity.
• Ingress Protection (IP), Dust, and Water tests – To test resistance to dust intrusion and water (dripping, spraying, and submersion depending on the rating), respectively.
• Temperature/humidity/altitude chambers – To test resistance to atmospheric extremes.

Safe handling, bringing safety home.

The first thing to avoid is the industrial outage that could affect hundreds of employees. Other than that, it can also terminate equipment worth millions, and bring production and revenue to closure. It is highly important to have a maintenance team to rely on especially with tools that are tough enough to survive the dust, water, falls, and impacts common in industrial settings. All professionals would demand to see the same level of accuracy, performance, and reliability from their tools.

Safety standards to live by

The Switzerland-based International Electro-technical Commission (IEC) 61010 has established the Measurement Category or what you’ll be familiar with (CAT) and they also have voltage ratings for electrical environments. These CAT ratings are based on how high-energy transient travels through the network resistance of the electrical installation. The ratings will help determine if the tools can withstand voltage transients.

• A single-phase receptacle-connected loads such as appliances and portable tools. – CAT II
• The three-phase distribution including single-phase commercial lighting and equipment in fixed locations such as switchgear and polyphase motors. – CAT III
• The 3-phase at the utility connection, outdoor conductors, electricity meters, and service entrances. – CAT IV

CAT Ratings…

To be exact, a high CAT number will refer to an electrical environment with higher power available and higher energy transients. Thus, a multimeter designed to a CAT III standard is resistant to higher energy transients than one designed to CAT II standards.

Forensic investigations have determined that without a Measurement Category circumstances might get more dangerous. If the rating of interior test equipment does not match the task, it will lead to an explosion if not used properly. Therefore, it is of utmost importance to make sure that your electrical testing tools have been independently evaluated. Having this kind of evaluation can you only be certain that your tools can withstand voltage transients. Moreover, the main goal is to certify that your test device meets the electrical safety standard. Standardization bodies, such as the IEC and NFPA, are not responsible for enforcing their test tool safety standards. Ultimately, any test instrument you use should be certified by at least one independent testing agency.

Let’s admit that even the most careful person can make mistakes that’s why electrical safety standards are important. Test instruments should help back you up. Moreover, it should also provide you with the right protection against inappropriate voltages. To meet the demands of today’s high-energy, high-hazard workplace, quality manufacturers like Fluke continue to improve their test instruments to make them safer and more reliable. Fluke goes a step further in designing and building our test tools with stout input protection. Ultimately, these are tools that are reliable and safe for every user.

Here are five mistakes to avoid in the field:

1. Don’t use outdated or defective test equipment.
2. Never neglect to properly inspect test instruments and test leads for damage or possible contamination.
3. Don’t use the improperly rated test tools for the job.
4. Stop replacing original fuses with inadequate ones.
5. Don’t work on a live voltage without proper preparation.

It’s vitally important to take safety precautions when working with electricity. Remember that you are the most valuable asset in the field. Following organizational measures and safety standards help avoid and prevent harmful and dangerous circumstances.

We at Presidium Corporation are ready to support you with highly qualified products and trained specialists! We carry the latest technology products and can cater to most industries in the Philippines. Want to know more about our products? Contact us now +632 82515165. Or visit our website at www.presidium.ph

In measuring both ac and dc current, Hall Effect clamp meters can measure up to the kilohertz (1000 Hz) range. With the same current transformer types, Hall Effect clamp meters use rigid iron jaws to deliberate the magnetic field that encompasses the conductor being measured.

The jaws are not wrapped by copper wires, not the same as current transformer clamp meters. In addition, the magnetic field produced by the conductor is absorbed across one or more gaps in the core after the jaws are clamped around the conductor. The point where the jaw tips of a Hall Effect clamp meter meet.

When the jaw tips of a Hall Effect clamp meter meet, a gap exists. It creates an air pocket that the magnetic field (aka magnetic flux) must jump. The core will not saturate when the gap limits the magnetic flux.

In contrast, the jaws of an ac-only current transformer clamp are flush when closed. When opened, the tips of the jaws show bare metal core faces.

Within the gap, there’s a thin plastic molding covering the semiconductor known as a Hall Effect sensor – it is a transducer that differs its output voltage when reacting to magnetic fields, in this case, the magnetic field of the conductor or wire being measured. The objective is to measure the magnetic flux directly. The output voltage from the sensor then improved and mounted to represent the current flowing through the conductor that lies inside the jaws of the clamp.

How the Hall Effect clamp meters work

While the current flow within the conductor is being measured. The iron core is formed by the jaws of a Hall Effect clamp meter that permits the magnetic field to effortlessly pass through easily.

In the case of the magnetic field (flux) that comes to that small air gap in the tips of the jaw, the field must jump that gap. When the gap is small, the field stays determined across the gap. Therefore, the Hall Effect sensor, which sits in the gap—produces a voltage proportional to the magnetic flux. The gap that the clamp transforms into a current reading.

Of all Hall Effect devices, the dc magnetic fields are concentrated through the core – like a permanent magnet sticking iron. Clamps require the reading to be “zeroed” before taking a measurement to eliminate offsets. The dc magnetic field of the earth and the possibility of other magnetic fields near the measurement site.

To learn more about clamp meters, visit https://presidium.ph/product-category/products/fluke-industrial-group-tools/clamp-meters/.

To measure ac or dc voltage:

1. Turn the meter’s dial to the proper voltage function ().
2. Link the black test lead to the COM terminal and the red test probe to the V terminal, specified by on the Fluke 381.
3. Measure the voltage by moving the probes to the desired test points of the circuit.
4. View the reading in the display.

To measure resistance or continuity:

1. Turn the dial to.
2. Remove power from the circuit being tested.
3. Connect the black test probe to the COM terminal and
4. The red test probe to terminal.
5. Measure the resistance by moving the probes to the desired test points of the circuit.
6. View the reading on the display.

If the resistance is < 30 Ω, continuity is indicated by a beeper continuously sounding. If the display reads OL, the circuit is open or the resistance being measured is greater than the meter’s resistance range.

To measure frequency (on the Fluke 381):

1. Turn the dial to.
2. Align to the center the jaw or flexible probe around the measurement source.
3. Push the yellow shift button (‍on the Fluke 381) to shift to Hz.
4. View the measurement in the display.

To measure capacitance (on Fluke 370 series clamp meters)

1. Turn the dial to.
2. Remove power from the circuit being tested.
3. Connect the black test probe to the COM terminal and the red test probe to the terminal.
4. Measure the resistance by touching the probes to the desired test points of the circuit.
5. View the reading on the display.

Remember, the more you use, the more familiar you become in measuring signal using test probes. Visit our website at www.presidium.ph to know more about our products.

Obtaining the precise temperature measurements of electrical equipment with the use of thermal cameras can be difficult until you know exactly what you are looking for. Because most electrical components are made of bare metal, emissivity is low which can make the temperature measurement unreliable.

Emissivity is the ratio of how well materials radiate infrared energy. Its values fall between 0.0 and 1.0. When equipment measures 1.0 it is considered a perfect radiator. However, there are no perfect radiators, because the material is the basis of an object’s emissivity. The aim of why it is hard to use infrared technology to conduct quantitative inspections which requires accurate temperature measurements, this is why many prefer qualitative inspections, it focuses on the apparent temperature difference between comparable equipment under comparable loads or the same equipment under comparable loads.

Electrical anomalies can be detected easily if you know what you are looking for. Electrical circuits with current flowing through it produce heat. That’s why each time you inspect an electrical component it is hot. The thermal pattern plays an important role in detecting electrical system anomalies. The biggest part of abnormal heating in electrical systems is normally caused by abnormal electrical resistance on a contact surface. The improved resistance could come from Phase on phase short, winding to winding resistance imbalance, and Insulation breakdown.

The area of the highest thermal energy is at the connection point; the circuit gets colder when it is farther from the contact point. The greatest amount of heat is generated at the point of resistance and then it conducts away from its point of origin, which leads to a telltale pattern.

Interpreting emissivity in thermal images

The emissivity depends on the viewing angle, surface condition, spectral wavelength, and temperature. Almost all nonmetallic materials are efficient radiation of energy. Infrared cameras have the capacity to change the emissivity settings. The user of the camera can make adjustments to get closer to the surface temperature. Keep in mind, that if the emissivity is less than 0.60, you cannot obtain an accurate temperature reading; there are also other factors that can affect the temperature reading.

Inaccurate temperature can be a sign of trouble ahead. Prevent the danger from happening by checking equipment temperature meticulously. With Fluke thermal cameras you can detect issues before they become problems. Designed for everyday use, in the toughest industrial environments, Fluke offers infrared cameras for a wide range of applications. Reach us through info@presidium.ph for more information on thermal cameras or visit https://presidium.ph/product-category/products/fluke-industrial-group-tools/infrared-cameras/.

Medical gas leaks in hospitals can affect a huge problem, especially for the maintenance teams. It is important to educate the team first on what to consider before testing medical gases and piping systems in the healthcare facility. You must consider the following factors in leak detection uses and restrictions of medical gases, risks associated with medical gases, and leak detection restrictions and options.

Uses and restrictions of medical gases

There are many variables that a hospital must consider inside their facility which includes healing patients, equipment, treatment, supplies, the safety of visitors, and their employees. But one of the most critical supplies that they need to manage is compressed medical gas which means they require a prescription for use and must be transported, stored, and dispensed under strict standards. Here are some examples of medical gases: Oxygen, Nitrogen, Nitrous Oxide, Carbon Dioxide, and Helium. These gases can be mixed individually together for patient diagnostics and to calibrate medical devices. In terms of restrictions, oxygen, and nitrous oxide are vaporous, it is essential to monitor the storage and distribution systems.

Risks associated with medical gas leaks

In transporting medical gases to healthcare facilities, it is a must to inspect the components for the leak, because exposure to medical gases can injure hospital staff. Exposure of gases comes from waste anesthetic gases. Leaks happen when the system is connected and disconnected. The volatility of these gases contains a potential fire hazard that can cause harm to healthcare workers. Also, the loss of pressure in the gas system can affect the quality of medical equipment. To prevent this from happening it is best to oversize a hospital’s air compressors.

Leak detection restrictions and options

Detecting leaks in compressed medical gas delivery is harder than finding leaks in normal compressed air systems, because of the nature of the gases and the challenging environment. One way to solve this problem is to spray approved leak detection liquid around the potential leak area and bubbles appear if there’s a leak. Another solution is the use of Fluke ii900 Sonic Industrial Imager; it lets you see leaks on an LCD screen from up to 50 meters away. It can be used to detect leaks in central air supply pipes and medical gas delivery systems because it is approved for use in areas where volatile gases like oxygen or nitrous oxide might be present.

 

To have an efficient gas leak detection it is very essential to educate yourself on what and what not to do before detecting the leak to prevent accidents from happening. Also, it is best if you have the proper tool that will efficiently help you detect the leak. Fluke ii900 Sonic Industrial Imager will help you detect the leak efficiently. Visit www.presidium.ph to learn more about our products. Contact us at +632 82515165 / +632 82570795.

In any electrical installation, some current will flow through the protective ground conductor to ground. This situation is usually called leakage current. Leakage current mostly flows in the insulation surrounding conductors and in the filters protecting electronic equipment around at home or at the office. The problems occur when leakage current on circuits protected by GFCIs (Ground Fault Current Interrupters) causes unnecessary and irregular tripping. In most cases, it can cause a rise in voltage on accessible conductive parts.

Insulation has both electrical resistance and capacitance as it conducts current through both paths. Even with the high resistance of insulation, little current can actually leak. However, if the insulation is old or damaged, the resistance is lower and ample current may flow. Moreover, longer conductors with higher capacitance cause more leakage current. At GFCI breaker manufacturers, they recommend one-way feeder length to be limited to 250 feet (76.2 m), maximum.

On electric equipment, it contains filters intended to protect against voltage surges and other disruptions. These filters typically have capacitors on the input, which adds to the overall capacitance of the wiring system and the overall level of leakage current.

For more leakage current basics and its measurement and effects, head on to https://presidium.ph/ for the high-equipment insulation testers to prevent future leakage current. Get a quote now!

Safety is the utmost important reminder to anyone who works with or around electricity. It manages what you wear, how you work, and the tools you carry. And by tools, we mean all the tools you carry, not just battery-operated test tools. 91% of electrical workers approved that insulated hand tools are the most critical when working on electrical equipment. From electricians to utility workers and maintenance to HVAC technicians, they carry insulated hand tools such as screwdrivers, pliers, and cutters along with the best electrician tools.

When working around electricity, the thing to remember is to de-energize the equipment, however, that’s not the case. Sometimes nearby energized equipment has unknown energy pathways that might unexpectedly feed voltage into the equipment you’re working on.

Insulated hand tools safety

When hazardous and unpredictable situations occur, insulated tools provide an extra measure of protection against it. And high quality insulated hand tools are engineered to protect you from electric shock and reduce the possibility of arc faults caused by short circuits.

The NFPA 70E standard requires insulated tools to be used when working on or near electricity greater than 50 V as this will protect workers from possible injuries and avoid companies from paying fines and liability costs from accidents.

It is perilous to understand the difference between a regular hand tool and an insulated tool. With lots of hand tools containing rubber coating over plastic handles, it is far different from an insulated hand tool. High quality insulated hand tools are constructed of a special combination of materials that can block potentially hazardous voltages and protection against electric shock.

Insulated tool certification

In using insulated hand tools, one must be certified and must undergo stringent testing by third-party labs to prove that the protection works and the tools can withstand hard use, extreme temperatures, and even live flame. Importantly, they must also comply with international standards including IEC 60900 and ASTM F1505.

The level of protection that Fluke engineered for the new line of insulated tools goes beyond research. An application from the same stringent requires safety, reliability, and ergonomics to our insulated hand tools that we require of our handheld test and measurement tools. They are precision-engineered of CMV steel for superior durability and manufactured using the most advanced techniques in state-of-the-art facilities in Germany.

Safe and ergonomic

Fluke insulated hand tools are also designed to minimize wear and tear. They are ergonomically designed to adjust to your hand to diminish strain and weakness and help prevent repetitive motion injuries. Our insulated pliers and cutters give you more gripping strength and are slim enough to more easily access jammed junction boxes and panels.

When working with live equipment and not sure how much will protect you from your regular hand tools, get one now from Presidium’s Insulated Hand Tools. Visit https://presidium.ph/ for the high-quality insulated tools for easier work and for your protection.

How did you measure ac accurately before there were true-rms DMMs? There were three kinds of precision rms meters available to me. The available types were all analog; the electrodynamic, the iron vane, and the thermocouple. They were all fragile, requiring careful handling to achieve accurate measurements and avoid damage. They were also slow to respond and presented a significant load to the measured circuit.

How different it is today, with many digital multimeters featuring true-rms ac measurement capability. Today’s meters are rugged, respond quickly, are more sensitive, and present the results with easy to read, digital clarity. But there are some subtle points you should be aware of when making rms measurements.

Most DMMs today measure the ac-coupled true-rms signal, rejecting the dc component if any is present. A few models, such as the Fluke 189, offer the additional option of measuring ac+dc true-rms, calculating the total rms value with the dc component present. Why the difference? When should you use one versus the other?

In a properly operating power distribution system supplied through transformers, only ac should be present, so the ac-coupled measurement offered by most DMMs is appropriate. And, when a diode fails in a motor drive rectifier circuit, it’s usually more effective to detect the failure by observing a reading in the dc voltage function which rejects the ac component.

Then, there’s the case where you would like to trace an audio signal through an amplifier circuit. That signal might exist on the collector of a transistor where a dc bias current is also present. Here again, when you want to separate the ac and dc components, the ac-coupled mode of the DMM is the correct one to use.

One case for measuring ac+dc occurs in the output of unfiltered dc power supply where a significant ac ripple voltage is present on the dc signal. Since a resistive heater or incandescent lamp connected to such a supply will respond to the total energy available, an ac+dc measurement will more accurately indicate how the load might react.

What can you do if you have only the ac-coupled rms measurement capability in your DMM and you want to measure the combined ac and dc energy? Bring on the calculator.

You can first measure the ac voltage and then the dc, recording both values. Next, you square both terms and add these squared values together. Finally, you take the square root of the sum and you have the ac+dc true-rms value of the signal.

A variation of this technique may be used to investigate the ac output of an electronic motor drive by using the low pass filter function available on the Fluke 87V.

The primary signal of interest on the output of such a drive is the low-frequency signal that drives the motor. The low pass filter of the 87V isolates this signal so you can make accurate measurements of its frequency and true-rms voltage.

When you don’t use the filter, you get a much higher reading, because the measured signal now includes all the switching voltages used to create the motor drive voltage.

To determine the rms value of this difference, you can do the following:

1. Measure the total voltage and record the value.
2. Measure the voltage with the low pass filter on and record that value.
3. Now, square both terms and subtract the second squared value from the first.
4. Finally, take the square root of the result and you will have the true-rms value of all the excess energy that was not filtered, within the bandwidth of the meter’s input.

One case where rms results may be added or subtracted directly is at your household panel, where the sum of the two 120V legs is indeed 240V. Those two signals are coherent. Visit https://presidium.ph/ to get a compact true-rms meter for accurate electrical installation and troubleshooting.