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Calibrating vintage multimeter (derp.foo)

submitted 1 year ago* (last edited 1 year ago) by [email protected] to c/[email protected]

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I've recently acquired an uncalibrated Philips PM2534 (edit: the battery-backed factory calibration data was lost due to the battery running out). I'm looking into somehow getting it calibrated. However, the calibration procedure is rather involved, and requires such things as an exact 300V DC (the service manual recommends using a Fuke 5700).

Anybody know of a way to have this multimeter calibrated? I'm a hobbyist and don't really need such things as traceability and certificates.

Edit: I live in the Netherlands.

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[–] [email protected] 1 points 1 year ago* (last edited 1 year ago)

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 V~rms~ = 1 ÷ √2 × V~peak~, 230VAC has a V~peak~ 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.