Fnirsi 2C53P 50-MHz Dual-Channel Oscilloscope (Review)

When I received the Fnirsi 2C53P three-in-one 50 MHz dual-channel ‘flat-panel’ oscilloscope, the first thing that struck me was the side of the box saying ‘4-bit Half-true RMS Value’. There are four features highlighted on the box, and this is one of them. A curious choice for an oscilloscope, isn’t it? Also, I wonder what it means. The third highlight reads ‘Intelligent Anti Burning’. This refers to the fuses inside the device that protect it against high voltages and current overloads.
 

Unpacking the Fnirsi 2C53P

Inside the box is a zippered semi-hard case containing the oscilloscope, a manual, and a bag with two 100 MHz P6100 oscilloscope probes. A second bag contains a set of multimeter probes, a short USB-C cable, and a cable with two crocodile clamps on one side and a micro-BNC on the other.

The oscilloscope itself is protected by a paper-plastic bag. Unwrapping it reveals a neat looking device. It measures about 145 mm by 100 mm by 35 mm, and it weighs approx. 370 grams. The front side only has a 4.3-inch touch display.

On the rear side is a foldable stand that, at least fresh out of the box, provides stable, adjustable tilted positions down to about 40°. The label states that there is a 4000 mAh battery (lithium) inside and that a 5 V/2 A charger is needed. A charger is not included in the box.

Connectors All Around

On the top side of the Fnirsi 2C53P are the two BNC connectors for the oscilloscope probe and the connector for the signal generator. On the right side are four isolated banana sockets for the multimeter. They are all Fnirsi blue, so be careful when connecting the ground lead. The top socket has icons for voltage, resistance, diode, capacity, and temperature. The bottom two are for current measurements, up to 10 A. On the left side is a USB-C socket, a reset pinhole, and the power switch. The latter is ugly and cheap and looks a bit like a microphone, but that’s an unimportant detail.
 

First Power On

After pressing the power button, you are asked to choose a language. It can do Chinese, English, German, Portuguese, Spanish, Russian, Korean, and Japanese. The printed manual is only in Chinese, English, Russian, and Portuguese. Once done, the instrument shows a nice swipable graphical menu where you can select which instrument you want to use or access the system settings.

In the settings menu, I found that my test device is running software version V1.8.2.2. From the Fnirsi website you can download only V1.7.1.5, so there is no point in upgrading the firmware yet. (It seems that the first two digits indicate the application software version, whereas the latter two digits are the FPGA firmware version.) The settings menu also lets you switch off the annoying beep that sounds for every key press, and you can define which function (none, oscilloscope, multimeter, or signal generator) is activated at power on.

The Oscilloscope

As the Fnirsi 2C53P is sold as a multifunction oscilloscope, like the Fnirsi 2C23T, let us first look at the oscilloscope. The first thing I noticed was that the two signal traces have almost the same light blue color. However, I found that if you go into the device’s main settings menu and change the theme color to blue (default is yellow), then channel 1 becomes yellow. The logic eludes me, but who cares as long as it does the trick. Note that my probes did not come with a yellow marker ring :-(.
 

Nice Touchscreen

Using the touchscreen is nice, albeit a bit sensitive. The traces, trigger level and cursors can be dragged up and down and left and right. To zoom in (horizontal scale), tap in the right half of the screen, to zoom out, tap in the left half.

Parameter selection is a bit confusing at first, as the possible values are presented as a wheel that you must spin. The display rolls over, i.e. the upper limit follows the lower limit and vice versa, but the selection does not. If you want to select the upper limit while being at the lower limit, you have to spin the wheel all the way up. For the vertical scale, this presentation is okay as there are many values. For the probe coupling, on the other hand, there are only two values, AC and DC (no GND), and they are shown as a list of five alternating ‘DC’ – ‘AC’ values. A slide switch would have been easier here.

Comparing Two Scopes

I switched on the built-in signal generator and connected channel 1 to its output to get a 1-kHz sine on the display. I also connected another oscilloscope (a Siglent SDS 1102X) for comparison. The sine wave was rock steady on the reference scope but wiggled a bit on the 2C53P. Both measured a frequency of 993 Hz (which is a bit strange for a DDS; setting it to 1008 Hz resulted in 1 kHz), but the 2C53P showed a peak-peak value of 3.28 V whereas the ref scope showed 3.06 V. The signal generator output was set to 3.0 V.

No Glitches for Me

Activating the second channel and connecting it to the same source (the internal DDS) produced an identical trace. Some users have reported glitches on one of the two traces, but I didn’t see any. Maybe my device is running corrected firmware? However, I did find that triggering wasn’t super stable, showing horizontal jitter and trigger misses once in a while.
 

DDS Signal Generator

The signal generator is easy to use. It features twelve waveforms, one of which being a DC voltage. The frequency is set by typing a value on a numerical keypad. Amplitude and duty cycle (only works with the rectangle wave) have a slider, but you can also punch in a number. There is no adjustable DC offset.

Setting the frequency to 10 MHz with a 3 V amplitude resulted in 2.76 V_PP on the reference scope (probe ×10) while the 2C53P said it was 2.64 V_PP (probe ×10, 20 MHz bandwidth limit off). Officially, the signal generator can only do the sine wave up to 10 MHz, but I found that the triangle and square waves worked too. The other signals won’t go above 5 MHz, even though the frequency value can be set higher.

4.5-Digit Multimeter

The multimeter starts up in auto mode. In this mode, it decides all by itself what it thinks it should measure. This works for AC & DC voltage, resistance and continuity, but it didn’t detect a capacitor or a diode. To select a mode yourself, tap the ‘Gear’ button. The Function button works too.
 

The display consists of a large value (1,9999 counts), a semi-analog bar graph and an oscilloscope-like trend window with minimum and maximum values. Up to five measurements of any type can be stored on the screen too. Therefore, you can e.g. record a resistance value, the voltage over it and the current through it without needing to write anything down.

Colors

As I mentioned at the beginning of this review, the sockets for the multimeter are all blue. However, the multimeter tells you how to connect the probes by placing a red and black dot on the right of the screen in the order of the sockets. Note that, for the multimeter, I preferred the yellow color theme as it greatly improves the readability of the ‘analog’ scale.

Precision

Precision-wise, Fnirsi claims 0.5% precision for DC voltages, and that is indeed what I observed when compared to my reference Fluke 189. The precision of 0.5% is quite a lot for a 19999-count reading (±100), so one might wonder if that many digits are really useful. Maybe when doing relative measurements?

True RMS After All

After carefully reading the manual, I think I know why what is meant with ‘4-bit Half-true RMS Value’ as printed on the box (see above). It is probably a translation error, and it should be ‘4.5-digit True-RMS Value’. That sounds much better than half-true RMS.

Conclusion

The Fnirsi 2C53P 50 MHz Dual-Channel Flat-panel Oscilloscope definitely is a nice device, and certainly worth the money. I wouldn’t consider it a precision instrument, but it is practical and very portable. It is quick to learn and then easy to use. Switching between instruments is fast. Its battery life is good, and the device will run for several hours on a single charge. After more than four hours of continuous operation, the battery charge indicator still had one third left. This means that you don’t have to switch it off all the time. As the signal generator can work together with the oscilloscope and the multimeter, deactivating it may make the battery last a bit longer. The only thing I hope for is a firmware update that corrects the quirks of the Fnirsi 2C53P, and especially improve triggering. But maybe that’s a weakness in the hardware.