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FNIRSI · FNIRSI 2C53P 3-in-1 50MHz Oscilloscope Multimeter DDS Signal Generator | 2 Channel Oscilloscope, 250MS/s Sampling, 19999 Counts Automotive Multimeter with 4.3'' Touchscreen, X-Y Mode, FFT Analysis
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A pocket instrument combining a two channel oscilloscope rated at 50 MHz bandwidth and 250 MS/s, a 19999 count multimeter with five simultaneous readings and minimum and maximum capture, and a DDS signal generator offering twelve waveforms to 10 MHz, on a 4.3 inch 480 by 272 IPS touch screen with 4000 mAh for about four hours. The scope numbers are honest but tight, and the sample rate per channel is unstated. The deciding gap is on the meter side, where there is no measurement category rating at all.
Fifty megahertz on 250 megasamples is the tightest number here
Bandwidth and sample rate are quoted together in the first bullet, and they constrain each other.
Sampling theory says that to reconstruct a signal without aliasing you must sample at more than twice its highest frequency component. That gives 100 MS/s as the absolute floor for a 50 MHz input, and a floor is not where you want to live. With barely two samples per cycle the reconstruction has no information about the shape between them, so a digital scope would have to guess.
In practice designers want four to five samples per cycle at the rated bandwidth, which lets sine interpolation draw something faithful, and considerably more if the interesting part is the leading edge of a pulse rather than a repetitive sine. 250 MS/s against 50 MHz is five to one. That is a legitimate ratio and it is also the minimum respectable one.
Which brings up the unstated figure. This is a two channel instrument, and the listing does not say whether 250 MS/s is available on each channel or shared between them. If the converter is shared, turning on the second channel drops each to 125 MS/s, which is two and a half samples per cycle at the top of the range. That is the single most useful question to ask before buying, and the page does not answer it.
Thirty four pixels per division is the screen ceiling
A 4.3 inch IPS touch screen at 480 by 272 is described in the bullet as high resolution. Work out what it means for reading a waveform.
An oscilloscope graticule is conventionally eight divisions tall. The listing does not state the graticule, but on that convention 272 vertical pixels gives about 34 pixels per division. One pixel is therefore about three percent of a division, which is the finest amplitude difference you can resolve by looking at the trace.
That is enough to see a signal, judge its shape, spot ringing and find a glitch. It is coarse for judging the size of a few percent of overshoot or the depth of ripple by eye, which is why on screens this size you lean on the numeric measurement readouts rather than the trace. Five simultaneous measured values on the meter side and automatic measurements on the scope side are doing that job.
The touch interface deserves credit in the same breath. On a handheld the alternative is a nest of small buttons and nested menus, and being able to drag a cursor or pinch a timebase is a real improvement in how fast you can work. One key AUTO, mentioned in the third bullet, matters for the same reason.
The multimeter half has 19999 counts and no stated category rating
19999 counts is a genuinely good number. It means the display can show just under twenty thousand steps before changing range, which is roughly four and a half digits and a step finer than the common handheld figures. Watching a small drift on top of a large reading is exactly where that resolution pays.
What is not on the page is any measurement category rating, any maximum input voltage for the meter, or any mention of fusing on the current ranges.
A category rating is not a voltage number. It describes the transient energy the instrument has been built and tested to survive at a given point in an installation, because a fault on a distribution board delivers far more energy into a meter than the same nominal voltage at a wall socket. An instrument with no rating is not thereby unsafe on a bench, but it is undocumented for anything beyond it. Our explainer on what a category rating on a meter means covers how the levels are assigned.
The practical rule follows directly. Treat this as an electronics bench and low voltage service instrument, which is plainly what it was designed for. Keep it off panels and distribution boards until a rating and an input limit are confirmed in writing, and use something rated for the job instead. Our roundup of multimeters for electronics repair covers the kind of work this suits.
Twelve waveforms to ten megahertz, and what a generator earns on a bench
Direct digital synthesis works by stepping through a stored table of sample values at a fixed clock. Change the size of the step and you change the output frequency, with very fine resolution and no settling time, and change the contents of the table and you change the shape. That is where twelve waveforms comes from, and why the generator can sit alongside the scope without adding much hardware.
The reason it belongs on a service instrument is that it closes the loop. Inject a known sine into the input of a stage and look at the output on the same screen, and you have a gain and a phase figure. Sweep it and you have a rough filter response. Drive a sensor input with a square wave and you can prove a board is dead rather than mis-wired.
Three figures a generator needs are absent: the output amplitude range, the output impedance, and any amplitude accuracy. Impedance in particular changes what you can connect it to, because a source expecting a matched load behaves differently into a high impedance input.
FFT, X-Y mode and the record length that is not published
The analysis features in the fourth bullet are the ones that separate this from a basic scope. X-Y mode plots one channel against the other, which turns a phase difference into a visible ellipse and makes a frequency ratio a closed figure rather than two traces you have to compare. FFT converts a time record into a spectrum, which is how you see that a supposedly clean supply has a harmonic sitting on it.
Both of those depend on memory depth, and memory depth is not published.
| Specification | Published in the listing |
|---|---|
| Oscilloscope bandwidth | 50 MHz, two channels |
| Sample rate | 250 MS/s |
| Trigger modes | Automatic, normal, single |
| Analysis | X-Y mode, FFT spectrum |
| Multimeter resolution | 19999 counts, five measured values, minimum and maximum |
| Signal generator | 12 waveforms, up to 10 MHz output |
| Display | 4.3 inch IPS touch, 480 by 272 |
| Battery | 4000 mAh, about 4 hours, Type-C charging |
| Record length | Not stated in the listing bullets |
| Sample rate per channel or shared | Not stated in the listing bullets |
| Vertical accuracy and sensitivity | Not stated in the listing bullets |
| Meter input voltage limit | Not stated in the listing bullets |
| Measurement category rating | Not stated in the listing bullets |
| Generator output amplitude and impedance | Not stated in the listing bullets |
Record length is worth a sentence of arithmetic. Capture window equals record length divided by sample rate, so at 250 MS/s a ten thousand point buffer holds forty microseconds of signal and a one million point buffer holds four milliseconds. Those two instruments feel completely different to use, because the short one forces you to trigger exactly on the event while the long one lets you catch it and go looking. The bullet promises waveform preservation, viewing and export without naming a buffer size or a file format.
The bench this belongs on, and the panel it does not
As a portable electronics and low voltage service instrument this is a sensible package. A scope that is honest about a modest bandwidth, a meter with better resolution than most handhelds, a generator that closes the measurement loop, FFT and X-Y for the awkward problems, and a battery that lasts a working session. For automotive sensor work, board level fault finding and small embedded systems it covers a lot of ground in one pocket.
It is not a mains instrument and the page does not claim to be one. The absent category rating settles that, and so does the absent input limit. Nor is it the choice if you need long captures, because record length is the specification the analysis features live or die by and it is not here. Establish the record length and the per channel sample rate first, and if either answer disappoints, the instrument is still fine for everything slower.
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Frequently Asked Questions
Is 250 MS/s enough for a 50 MHz bandwidth?
It is enough to be legitimate and not much more. Sampling theory sets the floor at just over twice the highest frequency present, but a floor is not a working margin. Oscilloscope designers generally want four to five samples per cycle at the rated bandwidth so that sine interpolation can draw a shape you can trust, and more than that if you care about the top of a fast edge. A ratio of five to one is therefore the minimum respectable figure, and it only holds if the full sample rate is available on the channel you are watching.
Does running both channels halve the sample rate?
The listing does not say, and that is the gap. Many handheld and entry level scopes have a single converter shared between the inputs, so engaging the second channel splits the rate in half; others have an independent converter per channel and keep the full figure. On a 50 MHz instrument the difference is the difference between a workable five samples per cycle and a marginal two and a half. Ask the maker which architecture this is before buying it for two channel work at the top of its range.
What does 19999 counts give you over a 6000 count meter?
Finer display resolution, nothing else by itself. Counts describe how many steps the display can show before it has to change range. A 6000 count meter reading 5 V resolves to a millivolt; a 19999 count meter on the same range resolves to a tenth of that. That is genuinely useful when you are watching a small change on top of a large reading. It is not an accuracy claim, and this listing publishes no accuracy figure to go with it.
Can I use the multimeter half on a mains panel?
Not on the strength of this page. There is no measurement category rating in the bullets and no maximum input voltage for the meter function. A category rating describes how much transient energy the instrument can absorb without the fault finding its way to your hands, and it is assigned by testing, not by the voltage printed on the display. An instrument with no stated rating should be kept to low voltage bench and electronics work until the figure is confirmed in writing.
What is DDS, and why is it on a handheld scope?
Direct digital synthesis builds a waveform by stepping through a stored table of sample values at a fixed clock rate. Changing the step size changes the frequency, which is why a DDS source switches instantly, holds a very fine frequency resolution and produces any shape you can put in the table, which is where twelve waveforms comes from. On a service instrument the point is that you can inject a known signal into a stage and then look at what comes out of it with the same device, rather than carrying two boxes.
What would you want added to this specification?
Record length first, because sample rate without memory depth does not tell you how long a capture you can hold. Then whether the sample rate is per channel, the vertical accuracy of the scope, the input voltage rating and measurement category of the meter, and the output amplitude range and impedance of the generator. None of those five appear in the bullets, and each one changes what the instrument can be used for.
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