The Siglent SHS 1102 hand-held oscilloscope is examined using internal square-wave signals that are provided for the purpose of compensating probes.
Greetings and welcome to our 59th Test and Measurement Video. This time we’ll examine the amazing Siglent SHS hand-held oscilloscope. This 100 MHz instrument with a sampling rate of one gigasample per second has two analog channel inputs that are totally insulated from ground and from each other, which means that it is safe to connect either of the probe ground return leads to a signal that is referenced to but floats above ground potential.
If such a connection is made with a conventional bench-type oscilloscope that is powered by premises mains, heavy fault current will flow through the oscilloscope, probe and circuit under test. If you are fortunate, the relatively light ground return lead will burn through, functioning as a fuse to interrupt the circuit before there is extensive damage.
In troubleshooting and repair as well as education, research and product development, it is often necessary to measure floating voltages that are ground referenced. One way this can be safely done with a grounded oscilloscope is to use a differential probe, which isolates both sides of the circuit from the ground plane. But the differential probe is expensive and in many shops it is not available. Some technicians saw off the grounding pin at the power cord plug, and that serves the purpose of isolating the bench-type instrument from the premises grounding system. But this dangerous expedient introduces a further hazard, which is that a wiring fault can expose the hapless technician or a passerby to electric shock.
The answer, as indicated earlier, is to use a portable hand-held, battery-powered oscilloscope with isolated inputs. This is especially true when working with variable frequency motor drives, where the internal DC bus actually operates at a higher voltage than the AC supply power due to the nature of the full-wave rectifier, where DC output relates to the peak-to-peak input voltage. Here both positive and negative sides of the circuit are referenced to and float far above ground potential.
To demonstrate the Siglent SHS 1102 in action, two possibilities suggest themselves. First, we could connect the instrument’s two channels to utility derived single-phase power, the probes tips connected to opposite lines so as to acquire two out-of-phase sine waves. We’ll do that in a future video that delves further into some properties of this amazing hand-held oscilloscope.
For now, we’ll connect the analog inputs for both channels to the internally generated 1 kHz square-wave signal that is available at a USB socket located beneath a cover on the right side of the unit.
For this purpose, an odd-looking device that resembles a USB plug attached to a smaller version of a standard AC plug is provided. Probe hook tips and ground return leads can be attached, and that is what we have done, attaching the two probes to opposite sides so as to display two 180-degree out-of-phase square waves.
While we are at it, we’ll see if the two probes are properly compensated for their respective channels. To do this, each probe is adjusted using a flat-blade screwdriver. When the probe is properly compensated, a well-formed square wave is displayed.
The two 180-degree out-of-phase square waves are now displayed. If we press Scope, bringing up the Scope menu, followed by Math, and scroll the operation to FFT, in split-screen format the time-domain representation is shown at the top of the screen and the frequency-domain representation is shown at the bottom. Here the Y-axis corresponds to amplitude, now expressed as power on a logarithmic scale rather than voltage on a lineal scale. And the X-axis corresponds to frequency, rather than time. So what we have is a line graph showing the power distribution at various frequencies.
The larger spike at the left of the display is the fundamental and it is labeled at the right: f = 1.00000 kHz. To the right, harmonics are shown, diminishing in amplitude as the frequency increases until they disappear below the noise floor.
Turning back on Channel 2 and pressing Scope followed by Display, we see that the format currently shown is YT. If we shift to XY format, the Lissajous pattern for the two 180-degree out-of-phase signals is shown. It consists of a diagonal line going from upper left to lower right.
Now if we press Channel One and go to Page 3 of the menu, Invert can be applied to Channel One. As it is turned on and off, the Lissajous pattern changes direction.
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