Top-tier bench-type, high-bandwidth mixed signal oscilloscopes, such as the Tektronix MSO 4000 series, have astronomical specifications with high price tags. They are appropriate in a research laboratory or for the development of sophisticated products.
For maintenance and repair, the hand-held, battery-powered instruments — unencumbered by great bandwidth and usually limited to two channels — are affordable alternatives that are built to last for years. An important aspect of the battery-powered instrument is that it is isolated from the premises electrical grounding system. So the ground return lead can safely connect to a wire or terminal in the circuit under investigation that is referenced to but floats above ground potential.
The Tektronix THS3024 and Fluke 190-502 ScopeMeter are both hand-held, battery-powered instruments having many desirable features including relatively high bandwidth and accompanying sampling rate. (The sampling rate must exceed twice the bandwidth if the highest frequency signals are to be displayed unambiguously. Most oscilloscopes have the bandwidth and sampling rate printed prominently on the front panel.) The Tektronix THS3024 has four channels with a 200-MHz bandwidth.
The Fluke 190-502 ScopeMeter is an excellent instrument with an incredibly clear interface. Here again the price is far from modest.
The BK Precision 2516 Hand-Held, battery-powered oscilloscope is highly regarded in the industry. With a solid, rugged form factor and user-friendly operator interface, it is a joy to use. A check of tech forums and reviews on vendor sites reveals there does not appear to be an issue of premature failure or malfunction. The instrument carries a generous three-year warranty. Students and independent technicians will be pleased to see the price, which is much lower than for competing oscilloscopes. The BK 2516 is available from various online sources for $3,000 or less.
The reason for the modest price is the unassuming bandwidth. The fact is that high-bandwidth instruments are expensive to build. That is because high frequency presents a host of difficulties in terms of probes, cabling, transmission lines, circuit board design, component placement, semiconductor design and just about every facet of instrument manufacture. The bottom line: Don’t purchase bandwidth that you will never use. The BK 2516 has a bandwidth of 100 MHz with a 1 GS/sec sampling rate.
If the bandwidth is sufficient for your needs, the BK 2516 is the way to go. That is because the machine is loaded with extensive, fully-realized assets. Opening the box, we find an impressive, detailed user manual that is a model of clarity, at once an elementary and yet advanced treatise on oscilloscope operation, with many valuable suggestions.
The instrument’s features include many that are found in far more expensive equipment. Like the much higher priced Fluke 190-502 ScopeMeter, the BK 2516 has three prominent buttons in a vertical column on the left side of the front panel. Starting at the top, they are labeled Scope, Meter and Record. This impressive instrument is not only an oscilloscope, but with separate probes and ports, a multimeter as well.
The BK 2516 is a multipurpose instrument. It functions primarily as a conventional hand-held oscilloscope. A press of the orange Scope key at the top makes five menus appear – Acquire, Display, Math, Horizon and Reference. As in most oscilloscopes, the Acquire tab takes you right into the system. Pressing F1 brings up the Acquisition submenu. The first choice is Sampling, which consists of Peak Detect and Average. Other choices are Sin X or X and Modes, which are Real Time and Equivalent Time. One more press of the Scope button brings up the other menu items Display, Math, Horizon and Reference.
Pressing Display, the user is able to set various aspects of the display appearance. None of these actually affects the signal, just its appearance on the screen. Type (of display) determines whether the trace is shown as Vectors, where the space between sample points in the display is filled, or alternatively, sample points only.
Persist sets the length of time each displayed sample point remains displayed. Choices are Off, One Second, Two Seconds, Five Seconds and Infinite.
Intensity and Brightness, calibrated as percentages, determine appearances of waveform and grid respectively.
The most-used format consists of YT, where the voltage displays in relation to the Y-axis and time displays in relation to the X-axis. An informative format is the XY, where one signal such as a sine wave is fed into Channel One, and another signal, which may be out of phase with it, is goes to Channel Two. The display consists of Lissajous patterns – lines, circles and ellipses, depicting the relations between these two signals.
Screen permits the user to go into normal mode or inverted mode, where display colors are reversed. Grid permits the user to turn off grids or both grids and axes. Menu Display permits the user to determine the length of time that menus remain – two seconds, five seconds, ten seconds, twenty seconds or infinite.
The third item in the acquisition menu is Math. As in high-tech bench-type oscilloscopes, there is a wealth of functionality here. Pressing F3 to go into the Math menu, the user can toggle among the choices — Add, Subtract, Multiply, Divide and Fast Fourier Transform (FFT) — by pressing F1 repeatedly.
FFT has only a single source, which can be set as Channel One or Channel Two, as opposed to the other Math operators, which require two sources, even if they are identical, i.e. coming from the same Channel.
FFT enables the user to view a signal simultaneously in the time domain and in the frequency domain. The information contained in these two quite different-looking displays is identical. The two graphics can be seen simultaneously whether in single or split-screen mode. The frequency domain representation is useful and provides users information that is difficult to extract by looking solely at the time domain representation.
BK 2516 offers a number of options that affect the appearance of the FFT display. One of these is the choice of the FFT windows. To select the window for viewing the FFT display, from the FFT menu select Windows. The choices are –
• Rectangular provides the best frequency resolution but the worst magnitude resolution. It is essentially the same as no modification. It is best for symmetric transients or bursts, equal-amplitude sine waves with fixed frequencies and broadband noise with a relatively slowly varying spectrum.
• Hanning has better frequency but poorer magnitude accuracy than the rectangular window. It is best for sine, periodic and narrow-band random noise.
• Hamming has a slightly better frequency resolution than the Hanning window. It is best for transients and bursts. The signal ranges vary markedly between before and after.
• Blackman offers the best magnitude resolution but the worst frequency resolution. The best use is for single frequency waveforms, to find higher order harmonics.
Another modification to the FFT display involves the arrangement of the time domain and frequency domain on the oscilloscope screen. The two representations can be shown in full-screen or split-screen formats. Additionally, the F4 button can determine the amount of zoom.
The BK 2516 has a built-in multimeter that can measure dc and ac voltage, dc and ac current, resistance, diodes, continuity and capacitance. To enter this mode, press Meter and the multimeter display appears. Large, legible numerals display the amount of voltage or other parameter, and a graphic illustrates the required probe configuration. To the right, Manual or Auto ranging is indicated. A bar graph further illustrates the metric.
The diode measurement is quite useful. Pressing F1 repeatedly, diode mode is entered. The instrument shows the forward voltage of general purpose diodes.
The continuity mode is useful for quick troubleshooting. There is an audible beep when the resistance is below a specified level.
The capacitance mode is great for checking the condition of capacitors. Before proceeding, be sure that the capacitor is fully discharged, because stored voltage can harm the instrument or the user. Press F1 to set the meter to read capacitance. The capacitance will be shown in microfarads or other appropriate units.
To summarize, the BK 2516 is a competent and useful instrument with many features. The limited bandwidth is sufficient for most electronic work, and the price is modest compared to higher bandwidth and four-channel oscilloscopes.