Secondly at least AC alternates, giving your muscles a break and possibly a chance to let go of the wire, DC isn’t that forgiving.
Interesting. Your comment made me read up on all of this. Note that, since Vrms = 1 ÷ √2 × Vpeak, 230VAC has a Vpeak of 325V, so in that respect, it should be pretty much equivalent to 300VDC. I figured that the ability for AC to induce heart fibrillations was the most dangerous factor in all of this, but I hadn’t figured in that DC induces tetanus and can also temporarily stop the heart.
It’s not the volts that kill you though, it’s the amps (the volts just make it easier). I found a table listing the effects of various amperages. It does present DC as generally more safe when compared against 60Hz AC, but I’m not sure how that generalises to the 50Hz AC we have here. I do conclude however that I should be limiting the output current to something something generally safe, like 20mA (which should be fine for a voltage reference). I’m thinking a PTC at the input and being conservative wrt capacitor sizing should do it.
Some of my co-students in university made an EKG apparatus. Our lecturer demanded that anything connected to the electrodes was to be powered by a single battery.
TBH, when it comes to an EKG apparatus I’d also be worried about common mode across the chest, or the power supply having a disastrous failure mode.
I prefer my Sn60Pb40 (…) The first couple of lead free solder brands I got just didn’t flow right.
Yeah, those were horrid. Even the supposedly excellent SAC305 gave me dull joints (tough it flowed adequately). Still, I can only recommend Sn100Ni+ (supposedly closely related to SN100C): flows well and gives me the shiny joints I crave. Having a good soldering iron (I’m using a Pinecil) helps with solderability.
I do however still have some rosin core Sn60Pb40 for reworking vintage electronics. And I do agree that it’s just better when it comes to wetting ability. The peace of mind when working with lead-free solder really is worth it though, especially with pets or small children.
my anxiety level is exponentially correlated to the working DC voltage and at 300VDC I’m definitely well in the thick rubbergloves territory.
Having been walloped by 230VAC, which is far more dangerous, I’m not too worried.
Looking at the schematic you linked above, the amperage is going to be low, which is reassuring. As a safety measure, I’m looking into running the thing off of a battery, so that if the worst comes to pass it simply won’t have the power to be dangerous (1A at 12V translates to a mere 40mA at 300V).
I’d be far more worried about using lead solder TBH (love my Sn100Ni+).
Their pricing for calibrating a device starts at around €400, which is rather more than I paid for this thing and way more expensive than building my own calibrator. So I guess I’ll have to do that…
(…) I have found an article explaining the build of the sources you need
Thank you! Not having to invent everything from scratch is going to make this a lot easier.
The device is supposedly a 6½ digit DMM yet I currently don’t even trust the first few digits when comparing it to a 3½ digit handheld Brymen DMM. Being reasonably sure that it’s at least more accurate than the Brymen would be nice, so 3½ digits.
I’ve got another desktop DMM, a 5½ digit GW Instek GDM-8255A, on the way, so I could conceivably just use that one as my local “standard” to calibrate against.
The problem however is that the Philips requires a large amount of references to calibrate against (just calibrating DC voltage requires 0V, 3V, 30V and 300V references). Building all references to recalibrate the whole thing would be rather involved, so I was trying to find an easier way.