FNIRSI SG-003A Signal Generator

    • by Clemens Valens
    • Reading time: 5 min

    The FNIRSI SG-003A Multi-Functional Signal Generator is a kind of process meter for generating and measuring voltages, currents, and frequencies compatible with PLCs and other (industrial) process control systems. However, the feature set of the SG-003A is interesting enough to make it also useful in the lab.

    Because its name can lead to confusion, let’s be clear from the start: the FNIRSI SG-003A Multi-Functional Signal Generator is not an arbitrary function or waveform generator. Instead, it is a kind of process meter for generating and measuring voltages, currents, or frequencies compatible with PLCs and other (industrial) process control systems. Think of 4 mA to 20 mA current loops, a 0 V to 10 V or 24 V control voltages, or a (pulse width modulated) frequency. However, the feature set of the SG-003A is interesting enough to make it also useful in the lab.

    FNIRSI SG-003A led tester
    Practical LED tester. It measures the forward voltage while you adjust the current in small steps.

    The FNIRSI SG-003A Signal Generator is a lightweight handheld device the size of a somewhat large packet of cigarettes. It comes packed in a nice box together with four 1-meter banana-to-crocodile cables, a USB charger with USB-C cable and a small manual in English. The cables are blue, red, yellow, and black, just like the four sockets at the top short side of the instrument.

    The front panel of the SG-003A has a 2.4″ color display and seven backlit silicone pushbuttons. The power button is located on the bottom short side on the left of the USB-C connector. Pushing it for about two seconds switches on the device. This brings up a display split in two, with a graph running on the top and some values at the bottom.

    Pressing the pushbuttons without reading the manual first is a bit useless, as the interface is not very intuitive. This is not helped by some strange labels like ‘Cuttent’ (I believe this should be ‘Current’), ‘Prei’ (Preset?) or ‘Ulse’ (Pulse?). The cursor keypad changes color depending on the order of the keys pressed.

    Despite its somewhat confusing user interface, it is worth trying to understand the instrument as it features some interesting functions.

    What can you do with the FNIRSI SG-003A?

    To do something useful with the SG-003A, you must first select a function. There can be two functions active at the same time: an input and an output. Both input and output can be configured for either current or voltage, independently of each other. The output can also be a frequency. An input or output function is selected by pressing the FN key (it turns red) followed by either the IN or the OUT key. The selected function is in yellow at the top of the screen. With the cursor keys, you can choose another one. The Enter key enables access to the function settings that you can adjust with the cursor and Enter keys. Press FN to accept the values and exit. If you press FN often enough, you return to the main screen. Depending on the function you selected, you can now use it. For an output, you must press Enter (On/Off) to enable the output. The signal is available on the red socket labeled OUT. An input must be connected to the blue and yellow sockets.


    FNIRSI SG-003A 24 V output
    Wow, 3-digit precision...

    The output value has a yellow digit that you can move left or right and increase or decrease. This way you can quickly set any value within the selected range. What you have now is a pretty precise programmable voltage, current or frequency generator. A 24.000 V output was measured by my Fluke 189 multimeter as 24.000 V. A current of 24.000 mA was measured as 23.982 mA. Similarly, frequencies turned out to be exact too. To obtain good precision values, let the device first warm up during 30 minutes or so.

    On the input side, things were also accurate. DC voltages up to 30 V can be measured and currents up to 24 mA. My SG-003A seems to have been calibrated, and maybe that is what it says in Chinese on the little yellow label that I found inside the box?

    When you press FN followed by Convert (down), the output follows the input. If the input was set to be a voltage and the output a current, then the SG-003A will function as a voltage-controlled current generator. Similarly, it can also be a voltage- or current-controlled frequency generator or a current-controlled voltage generator.

    Another nice feature is the automatic option. This lets you make the device ramp up and down for a programmable number of times (can be infinite, too). The ramp levels can, of course, be adjusted. On the ‘Curve’ display, you can see in basic oscilloscope mode how the inputs and outputs evolve.

    FNIRSI SG-003A oscilloscope curve
    Curve display. The white line is the input, the yellow line is the output.

    The FNIRSI SG-003A has some more features that you can discover for yourself.


    Like all the other FNIRSI instruments that have passed through my hands, the SG-003A is of excellent build quality. It looks nice and feels very rugged. The user interface is somewhat complicated, but once you’ve figured it out, the instrument behaves smoothly.

    Even though I do not have many processes to calibrate, I do consider the SG-003A a useful addition to my lab as it lets me generate precise currents (great for LED testing), voltages and frequencies in a simple and portable way. The convert function is nice too, even though I haven’t figured out (yet?) how to change the range of the output. And you can never have too many voltmeters, can you?



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