The Fnirsi S1 Multimeter: Smart With Large Display (review)

It appears that an electronics engineer can never have enough multimeters. New devices are regularly released that can do a bit more or a little differently than other multimeters. The Fnirsi S1 offers a large color display for just over thirty euros. It is also “smart”, meaning that it can detect whether a DC voltage, an AC voltage or a resistor is connected to its inputs and automatically shows the corresponding value on the display. It can also measure capacitance, diodes, temperature and frequency, and it has a built-in contactless voltage detector and an LED light. What more do you want? Well, the S1 cannot perform current measurements. But how important that is, depends on your personal use of this multimeter.

It Looks Like a Smartphone

After unpacking, the S1 appears as a slightly thick smartphone with the power button at the top. But the three push-buttons with the symbols below the display reveal that this is really a multimeter. The device is light, neatly finished, and it does not look cheap.

After switching on, a loud beep sounds and the word ‘Auto’ appears on the bright screen. The size of the letters shows that the measured value will also be large. Two four-digit values are shown (max. 9999). The digits of the first are 18 mm high, those of the second are slightly smaller (15 mm). The latter is used to show the frequency during AC measurements, and for temperature measurements it displays the value in °F.

The Fnirsi S1 Has a Flash Light

The measurement inputs are at the bottom and the backside has a “flash” light that can be switched on with the right button. The sensor for non-contact voltage (NCV) measurement is located below the On/Off button. The meter is powered by a built-in Li-ion battery that can be charged via a USB-C connector. According to the manufacturer, the operating time on one battery charge is approximately 5 hours. The meter switches off automatically after approximately 10 minutes.
 

Despite its low price, the meter comes with quite a few accessories. In addition to a set of fairly flexible test leads, you also get a USB-A-to-USB-C charging cable and a k-type temperature probe. The English manual is not so bad, most of it is understandable for an electronics engineer.

Possibilities of the Fnirsi S1

With only three buttons, the number of adjustment options on the S1 is limited, but that is probably on purpose. The meter is designed to quickly take the most important measurements without much hassle.

After switching on, the meter is always in Auto mode. Depending on the voltage or resistance connected, the S1 shows the measured value: AC voltage, DC voltage or a resistance value. For resistance values below 50 Ω, the (continuity) beeper also sounds. By pressing the large SEL key several times, you can manually switch between DC, AC, resistance/continuity, diode, capacitance, frequency and temperature.

Non-Contact Voltage Measurement

The left button is used to activate contactless voltage measurement (NCV), which shows the measured field as a bar graph. I must mention that this function is not very sensitive, my meter only responds if you hold it at one to two centimeters from a mains cable.

By pressing the left button again, you enter ‘Live’ mode, which allows you to determine which of the two contacts in a wall socket or extension box are connected to the live wire. Connect one test lead and insert its probe into one of the holes of the socket. The meter will beep at the live side. That can be quite useful (a replacement for the well-known voltage test screwdriver).
 

 

Multifunction Right Push-Button

Finally, there is the right push-button. By pressing it briefly, the measured value on the screen is frozen (Hold); pressing it again returns to the normal measuring mode. Pressing the button a little longer activates the light on the back. That can be useful, but it isn’t very bright.

The Fnirsi S1 in Use

In terms of accuracy, you should not expect too much from the Fnirsi S1 as the basic accuracy specified by the manufacturer is 0.8% for AC, DC and resistance. Yet, my review device appears to be much more accurate. I checked several values, and the accuracy was usually within 0.3%. Very nice for this price range!

The Auto mode appears to work surprisingly well, the meter almost always detects the input value correctly. Things only go wrong at low input voltages (below approximately 0.7 V) when the meter assumes that a resistor is connected. However, this is also mentioned in the manual and has to do with the fact that the meter in Auto mode applies a small voltage to the input pins to measure resistance. In such a case, it is best to manually switch to the AC or DC range with the SEL key.

Testing Auto Mode

To test the Auto mode, I even tried a sine wave superimposed on a DC voltage. That went very well: The meter always responds to the larger value of the two. If you switch manually, it will indicate the correct value for both AC and DC.
 

When measuring diodes, the S1 operates with a maximum voltage of 3.2 V and a current of 1 mA. That is sufficient to test almost all types of LEDs, in addition to diodes. Capacitance measurements should be within 4.5%, but on my sample the accuracy was within 2% compared to several other capacitance meters.

The Fnirsi S1 Goes Up to 28MHz...

I also examined the frequency measurement mode, and that yielded a surprise. According to Fnirsi, the measuring range is up to 10 MHz with an input sensitivity of 1.5 V_RMS. However, I could easily measure up to 10 MHz with a 0.7 V_RMS input signal. In fact, after increasing the input signal’s amplitude to 1.5 V_RMS, the meter measured frequencies up to 28 MHz. Not bad!

The temperature measurement with the supplied sensor was off by a few degrees at room temperature. Unfortunately, I could not get the accuracy stated in the manual (1%). According to the same manual, the sensor should be suitable for temperatures up to 1000 °C. I have not been able to verify whether this is really the case.
 

 

Safety First

Finally, a note about safety. According to the imprint on the front of the meter, the S1 is suitable for voltages up to 1000 V (Cat. III). I do have some doubts about that. The ground connection of the USB port (not the metal casing) is internally connected to the COM input. Although the meter cannot be used when the battery is being charged, this is not really safe. Therefore, use the device with some caution when measuring, for example, the mains voltage in your house. But don’t use it for higher voltages.

Conclusion

The Fnirsi S1 is a handy and cheap multimeter that has quite a few functions, but cannot measure currents. Whether that’s a dealbreaker or not depends on your personal usage. Apart from that, the instrument is very usable and quite accurate. It is somewhere in between a nice gadget and a serious multimeter. However, I must admit that the large, clear display and the Auto function do have their charms. Would I buy such an S1? Yes, probably, just to have one!
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