The versatile multimeter should not be the only weapon in your troubleshooting arsenal. A host of other useful tools has become more portable, affordable, and user-friendly.
This century is ending on the heels of a quiet revolution in handheld test tools. Under Moore's Law, computing power doubles every 18 months. Similarly, we're seeing the same trend with test equipment, especially in the more advanced units like power quality analyzers, harmonics analyzers, and handheld oscilloscopes. Even the more familiar tools like voltage testers and digital multimeters (DMMs) give you more bang for your buck than their predecessors.
Today's DMMs, for example, offer features unheard of just two years ago. Meanwhile, usability is up, and cost is down. The temperature tester has emerged from obscurity to become a mainstream tool for maintenance; thanks to quantum leaps in functionality combined with nosedives in cost.
Let's take a look at four general groups of handheld test tools to see how they can improve your efficiency.
Power quality analyzers, harmonics analyzers, and handheld oscilloscopes. This class of powerful handheld test tools goes beyond the capabilities of traditional multimeters and oscilloscopes. What drives their popularity?
• Power quality issues like harmonics, voltage sags and swells, transients, and noise require handheld tools that help us isolate problems.
• Energy management and cost-cutting efforts require us to make power and power factor measurements of individual loads.
• We must view and capture high-frequency signals, thanks to the spread of industrial electronics (PLCs, variable frequency drives) and networking technology. Portable and rugged, these instruments typically incorporate a combination of the following capabilities. They can:
• Measure power (W, kVAR, kVA, PF) and harmonics.
• Display and capture waveforms from 60 Hz power circuit signals to very fast signals, such as transients, data communications, and drive outputs.
• Store measurement or waveform data for later transfer to a computer for storage or analysis.
• Record measurements over time.
Originally, some of these devices were essentially general-purpose oscilloscopes, packaged for portability and fieldwork. However, they have recently made quantum leaps in power and ease of use. How?
First, advanced firmware makes automatic signal display (even of hard-to-trigger signals) user-friendly. The challenging part of operating a traditional scope is adjusting time base, vertical resolution, and trigger level. You can still do so with new instruments, but firmware eliminates the struggle.
Second, simple interfaces shorten the learning curve. Some tools incorporate menu 1selections in language you're familiar with, and use controls like those on a TV remote controller.
Many of these instruments are dual channel. They can display two voltage signals or a combination of voltage on one channel and current on the other. The firmware combines the two channels to calculate power (W, kVA, kVAR, PF).
Some instruments "deconstruct" the waveform and perform harmonic spectrum analysis on either or both inputs. When endowed with additional memory, these can be recorders or data loggers. You wind up with a combination power quality analyzer and general-purpose electronic troubleshooter. For example, let's say you are installing, maintaining, or troubleshooting an adjustable speed drive. You might look at the line side power connections to the drive first. At this point, you are making power quality measurements. You could check for voltage imbalance and resulting current imbalance on the line side, since these drives are even more sensitive to imbalance than across-the-line motors. You might also check the waveforms of voltage and current, and then analyze their harmonic spectrums.
You may be thinking: "I have a harmonic analyzer and a DMM. What advantage is there in combining the two?" Besides the cost-savings, think about when you trudge out to a job site; maybe a motor drive; while lugging a tool pouch, equipment manual, and test equipment. The more tasks you can accomplish with less equipment, the better.
You can also use the recorder to find voltage sags, which might trip the drive. You could also select a transient capture mode to look for capacitor-switching transients, which might cause the nuisance tripping. A real-time stamp tells you the second an event occurred. You could open the drive, measure the DC link, and check components such as diodes, capacitors, and transistors. You could check for attenuation and integrity of the high-frequency PLC control network signal. You could check the output of the drive, paying attention to overvoltage reflections on the PWM waveform, which might be damaging the motor insulation.
You can use your clamp accessory to check for ground loops or other sources of noise. At any point, you can record normal waveforms and later print them out or download them. If you go on vacation, you can pick up the test tool again without having to reread the manual, because the menu-like interface simplifies use of the instrument. It's not as simple as the DMM, but it's more powerful.
We're also seeing innovations in the electrical tester category; the simplest and lowest-cost test tools. Manufacturers have made improvements in ease-of-use, overall functionality, ruggedness, and safety. Let's look at the latest developments.
Voltage testers. The newest voltage testers use digital circuitry. The older versions used solenoids. This change alone results in quicker response time and longer instrument life. Properly designed, these testers can withstand worst-case transient voltages as high as 8000V. They typically use LED indicators set at the most common system voltages, both AC and DC. As with the original solenoid tester, test leads permanently attach to the instrument. The quality of the test leads and probes is a critical factor in the integrity of the tool, since they directly affect your safety. The leads and probes should have the highest safety rating available (CAT III-1000V).
Beyond the basic model is a tester with a limited resistance range and continuity. Continuity checks are low-resistance measurements (typically less than 25 ohms) used to check for a complete circuit. Some combination testers have nothing but an ON/OFF switch. If you turn one on and make contact with a circuit, it will first check for AC or DC voltage. If it senses no voltage, it automatically checks for resistance and continuity. This combination tester, unlike the simple voltage tester, has a digital display (similar to a true DMM) for more exact readouts.
Today's combination testers measure voltage and resistance, like their predecessors. However, they also measure current. The movement is toward more functionality in a one-step, one-hand operation. Advances in current sensor technology are making this a reality.
Digital multimeters (DMMs). The DMM usually has the basic measurement functions: volts, amps, and resistance. Frequency, dB (decibels), capacitance, and temperature are commonly available. Some DMMs include powerful recording features such as:
Min/Max/Average: This function allows you to capture voltage sags, inrush current, and other intermittent events. A meter with this feature displays the highest, lowest, and average (of all readings) values during the period it's recording. Typically, an event must exceed about 100ms (about six cycles at 60 Hz) for the meter to record it, so readings are rms values.
Continuity (or Open) capture: This function is useful for troubleshooting loose connections. You hook the meter up as an ohmmeter (no power in the circuit), and jiggle the wires. A bad connection shows up as a "beep."
Time stamp: An "elapsed time" stamp shows the total hr/min/sec since the start of recording until the event occurred. A real-time stamp tells you the actual day/hr/min/sec of the event.
Peak detect: Whereas Min/Max/Average records an rms value, Peak Detect records the highest peak value, on the negative or positive half-cycle that exceeds 1 ms or a quarter ms, depending on the meter. This is useful for capturing voltage transients and motor inrush. It's also helpful when you're measuring distorted voltage and current waveforms.
Some manufacturers view the DMM as part of a total measurement or maintenance system; just like the cell phone fits into a total communications system. You can set up a DMM with a computer interface to communicate with a computer. These meters send data to a computer in real-time, or store them to send later. Some have noise-immune optical interfaces and IrDa (infrared data) interfaces. Advanced meters can sample values such as voltage, current, or temperature over a given period and display the results as a trend plot. This provides a quick graphical way to identify high or low deviations from normal signals.
Temperature testers. The infrared thermometer provides quick non-contact temperature measurements. It's ideal for measuring surface temperatures of rotating, hard-to-reach, electrically live, or dangerously hot targets. With infrared technology, you can make the measurement in less than a second.
Although infrared thermometers are not quite as accurate as calibrated contact thermometers, their repeatability is excellent. Most modern infrared units include a bright laser beam for easy targeting. Other conveniences include a backlit dual display showing not only the measured temperature, but also the variation encountered during the measurement period (Min/Max).
You can use an infrared tester to look for electrical hotspots. If you measure a voltage drop in a circuit, the tester will help you find the bad connection or damaged wiring that's causing it.
In the past, your reputation depended on combining a few simple measurements and maybe some complicated ones with good troubleshooting procedures. Today, you can enhance your reputation with easy-to-make measurements that allow you to troubleshoot quickly and accurately.
Sidebar: The benefits of a time stamp
If you think of a time stamp as a frill, think again. A recent example of its power is the mysterious failure of a new circuit design. It happened several times when no one was around to observe it. Finally, the technician recorded the event and elapsed time to failure. He was able to repeat the test, duplicate the failure in the same period, and find a software bug; saving weeks in the development cycle.
Another example is an extrusion plant with a high failure rate of motors and barrel heaters on the evening shift. Electricians mounted several meters in locations throughout the plant and recorded readings the next day. They tracked their results over several days. The time stamps showed extreme voltage sags followed by extreme voltage peaks, shortly after the shift started. Then, there was a long period of low voltage beginning shortly after dinner. Operators were starting the 200 hp fire pump across the line and washing the outside of the building at sunset, thus creating the sags and peaks. What caused the low voltage? The operators plugged in dozens of personal space heaters at night. By installing a soft-start and a breakaway lock on the fire pump and adding temperature-controlled automatic doors and vents, the plant eliminated the voltage problems.