EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: AngraMelo on October 02, 2019, 07:09:49 pm
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Hey guys,
I have a Simpson 260 series 2 multimeter. It is measuring voltages just fine on all scales but resistance is measuring a bit too high on all of the resistance ranges. Around 10% higher than it should.
My questions is about the resistors inside the meter. I see people reforming old radios and test gear that have those large brown resistor (carbon?) are those the same type that are inside this Series 2? I know they drift with time and I believe this is what is happening to my meter.
Also, those old resistor seem way bigger than they regular modern ones, where they also 1/4w? even with that larger size?
On the manual there is a schematic but it doesnt say anything about the power dissipation on those, what size should I use? 1/4w is fine?. Given that my meter has no internal adjustment for the resistance measurements I think ill have to change them.
I think the resistors I have to change are R1, R2, R3 e R4.
http://www.simpson260.com/downloads/simpson_260-2_schematic.pdf (http://www.simpson260.com/downloads/simpson_260-2_schematic.pdf)
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Personally I wouldn't worry about it. Most analog multimeters are pretty poor ohmmeters.
If for example you are checking a 10 ohm resistor in circuit to see if it's OK, does it really matter if it appears to measure 11 or 12 ohms?
If you really need accuracy on an Ohms function, you need a more modern digital multimeter anyhow.
Just my .02 worth.
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Absolutely, I agree with completely.
It is not a matter of not having a better resistance meter it is just that given that I have the Simpson, I might as well put it to use. 10% is a bit much and can throw you off when trying to diagnose a issue or malfunction. It is a pretty nice meter that measures up to 5kV and having it working up to spec would be nice
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The resistors in the Simpson 260s are wire wound resisters, not carbon comp. Carbon resisters will drift too much. The resisters in the 260s are all odd values; like 990 ohms, 9990 ohms and the like. they use those values so that with each one in series with the meter movement, the exact circuit resistance will be 1 k Ohm, 10 k Ohm, etc. Go over to Simpson260.com, they have schematics and manuals for those meters. The other posters are correct, the Simpson 260 is only accurate to 2% (IIRC), if you need better accuracy get a decent digital meter.
Can you post pictures of that meter? The series 2s are ancient! My series 3 is dated 1958 IIRC and I think it was one of the later ones.
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PS I'm not 100% certain but I think the resisters used on the lower ohms ranges use larger wire and have a higher wattage than the others. They do that because the lower resistance will allow more current to flow and can cause more self-heating.
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Thank you for your input.
Ill post pictures of it tonight. It is in great condition. It looks exactly like the one on the simpson 260 website, it doesnt even have "series" written on it.
As I live in Brazil, this was even more of a find. Besides the battery contacts and the mentioned resistance measurements, the whole thing works very well for its age. It has no sign of ever having a leaky battery inside. The battery contacts are just worn, no big deal. A bit of contact cleaner and bending them back out a bit makes everything work a treat.