I just got the GPP-4323 couple days ago. TME had limited discount and it was the last in stock. The first impressions went from being impressed about the relatively compact form, well thought-out user interface and very quiet operation, to disappointment about unnecessary last digit for the not that great accuracy, to again being impressed by the low drift and stability especially of the lower range aux channels.
Let's get some less well known specs overview out first:
The readback resolution is 0.1 mV and 0.1 mA but the instrument is specified with horribly coarse 0.03%
+ 10 mV and 0.3%
+ 10 mA, both for setting and readback values, which almost nullifies the usefulness of the fourth digit beyond decimal point. In reality the accuracy is quite bit better, it seems this GW Instek is covering the imprecise zero offset and internal resistor parallel to the output which will affect the low current readings at higher voltages. The set and readback are not coupled into feedback loop, so they can both drift independently.
The CH1 and CH2 are identical main outputs, 0-33 V and 0-3.2 A (so a little more over the official datasheet range) while also being able to sink 0-33 V and 0-3.2 A in load mode, being limited by 50 W total input power. OVP and OCP limits go even more beoynd that range, 0.5-35 V and 0.05-3.5 A. There's rather large 470 uF capacitor and 470 Ohm parallel resistor at the output terminals.
CH1 and CH2 have internal relays to change into classic serial or parallel mode. They also have internal relays to switch over to load mode, really welcome innovation. The voltage at the jacks has to be low (<1V) or none to be able to switch between he source and any sink (CV, CC, CR) mode, otherwise it will fail with error message couple seconds later. That's perhaps why there is no front panel voltage reading under 1 V input but you can read it remotely. You can set 1.5-35 V in CV mode but if you are in CC or CR you can use the load basically down to zero or at least to very low values limited by lowest resistance of the loading circuitry. In practice I was able to sink 100 mA at 20 mV, 1 A at 200 mV, 3 A at 600 mV. That's totally usable to discharge any batteries in the available current range. The CR mode has only 1 Ohm to 1 kOhm range, so it's limited in range and resolution but still better than nothing. Unfortunately when you get back to supply mode the channel uses the same values last set for loading and doesn't go back to last used sourcing voltage and current.
CH3 and CH4 look symmetrical inside but are different. CH3 goes 0-16 V and 0-1.1 A and CH4 goes only 0-5.5 V and 0-1.1 A but it's significantly more accurate and stable, thanks to higher resolution per volt of the ADC/DAC. There's smaller 100 uF capacitor and 1 kOhm parallel resistor at the output terminals.
All channels are completely separate and isolated, major advantage against similarly priced multichannel supplies. From my simple test I saw no detectable change in the CH3 output when I put CH1 into source and CH2 into load mode, drawing and burning some 30 W.
You can have some idea from this 10 minute voltage stability reading. The power supply values include both set+readback inaccuracies together while I'm measuring the most stable CH4 with 34401A and it's stable down to the 0.1 mV:
Here are some voltage and current readings through the range with my uncalibrated Agilent 34401A. The short circuit current aren't much useful for absolute accuracy because in use there will be some portion of small current getting lost in the parallel resistor connected to the output, and I don't know at what input was it calibrated in factory. But it's useful to have some comparison across the channels. I also included another current measurement from the more accurate CH4 at 10 V, being loaded by CH1
https://docs.google.com/spreadsheets/d/e/2PACX-1vSAmuvfcysmZyoXO-G8Ks2CuzfTUr3kWx1BcEYiueAI9lsqgBrvoLWwYOEaJRnOpns1F91hRUq4cZEK/pubhtml?gid=0&single=true
CH2 stability, the worse of the main two channels based on power supply readback range of vlaues. Still, it's regulated well within 1 mV (tested without load). 0.2 mV per division.
CH3 stability, the rock solid aux channel, albeit limited only to 5.5 V
CH4, the better aux channel
Now for usability and user interface. In my opinion the front panel is well laid out, the controls are useful and easy to operate. For testing the supply when I need to change the output by small increments I use only the rotary encoder. It feels pretty good with noticeable but not too hard clicks. Unfortunately later I found that the resting position isn't so stable and there's small amount of play clockwise that can increment the value without moving to the next click. It doesn't happen often but sometimes I would find out that I dialed one more than I wanted. Otherwise I could count that each click was precisely one increment.
Memory button is strangely used only to save or load all channel presets. There is screenshot function but burried in System-Setting-Hardcopy. However it doesn't work! Both saving channel values recording and the "Hardcopy" doesn't save anything to the USB stick. I tried both 4GB ones with same result. Even worse, the Hardcopy button freezes your supply, you can't even turn any channel off until you remove the stick. And that's with latest, couple months old 1.16 firmware. The only thing what I found works on the USB stick is saving and recalling the channel presets. Quite limited function if you ask me.
Then there are more advanced functions of sequencing (for example you can make ramp up but you're very limited by 1 point-1change per second), delays, monitor alarms. You can also change the display style, there are 5 regular ones and two waveforms. But only the first one shows all 4 channels together with both set voltage and set current visible. If you don't need that or want to see only one channel at a time then it can be useful to have much larger font on the display. The look is quite pleasing, certainly better than average with good readability. Unfortunately the large LCD is also very reflective so at different angles you can see more what's on your desk or behind you rather than the power values. In darker corner it's not a problem.
Another problem recessed jacks, by that I mean both the safety EU style plugs and the indented lower panel. If you look at it down you won't see any of those channel labels. I solved it by printing transparent label on the bottom. Closer examination reveals venting holes under the display/button bump, so that's perhaps the reason for that shape, still doesn't explain why GW Instek couldn't label the channels at the bottom. There's also no color coding which could be certainly useful to orient yourself in the unusual CH4-CH1-GND-CH2-CH3 arrangement.
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