[I had no way] to precisely measure current. My other bench meters are analog, lowish impedance, and not precise enough to measure voltage drop across a small-value resistor. Additionally, my Simpson 260 and Simpson 160 meters don't agree on the 100 mA scales -- I believe the Simpson 160 is correct, but needed a way to figure out.
My experience is that digital voltmeters put too much current load on a circuit, when measuring DC current at tens of mA. Put another way: they have significant series resistance and change the circuit, and so change the current. Your A/D technology also puts a load on the circuit, you can read off the schematic or parts to determine that. But I found my Simpson 260 and other analog meters, put LESS load because they generally use 50uA movements (hence 20,000 ohms per volt, do the math). As to "figuring out the accuracy".....create a 10mA circuit from an accurately-measured battery and an accurately-measured resistor. Say 5V and 500 ohms, or whatever - the DVM can measure those fine, other resistors give other current sources, and math gives you the exact current. Many batteries can generally supply 10mA stable for minutes and hours or more, and your DVM can monitor their voltage anyway. Then make those circuits with the Simpsons and recalibrate the scales, and create conversion factors (or fitness for use choice) for each meter AND for each scale. YOu can use the same apparatus to calibrate your Apple II "meter". I prefer analog meters when making "runs" of comparative measurements. It's easy to see if one reading is "more" or "less" than another, the needle is literally in different positions. I've found variations in current measurements among several Simpson 260 meters (and among their scales) I've acquired. My guess is that some of the shunts were "cooked" by excessive current, or corroded by time and tide. I have not yet gone to the trouble of diagnosing them, I simply use the meters that have the best readings through the procedures noted. They are cheap today. Why? Given the "digital is better" bias these days, only a few people call out the Simpson 260 as a valued instrument - Dave McGuire for instance, in that email list we used to use. Jonathan, if you determine a cause for your analog meter's apparent errors, let me know. Herb Johnson old-school -- Herbert R. Johnson, New Jersey USA http://www.retrotechnology.com
But I found my Simpson 260 and other analog meters, put LESS load because they generally use 50uA movements (hence 20,000 ohms per volt, do the math).
Yep, one reason I don't have any non-Simpson analog meters anymore!
As to "figuring out the accuracy".....create a 10mA circuit from an accurately-measured battery and an accurately-measured resistor. Say 5V and 500 ohms, or whatever - the DVM can measure those fine, other resistors give other current sources, and math gives you the exact current. Many batteries can generally supply 10mA stable for minutes and hours or more, and your DVM can monitor their voltage anyway.
Exactly my plan. I just needed something I knew was accurate on the voltage measurement. That's the problem with two instruments you're uncertain of -- "a man with a watch always knows the time; a man with two watches is never sure!"
Why? Given the "digital is better" bias these days, only a few people call out the Simpson 260 as a valued instrument - Dave McGuire for instance, in that email list we used to use.
I prefer an analog meter for troubleshooting -- like you said, easier to detect an "is it off" condition, especially with intermittent circuits. And, the loading of the analog meter can be an advantage in many situations. My Simpson 260 is always on the bench, and I keep the Simpson 160 in my toolkit since it's just the tiny version of the 260.
Jonathan, if you determine a cause for your analog meter's apparent errors, let me know.
I opened it up this afternoon, it looks like the shunt for the 100 mA scale is wire (nichrome?) wrapped on a phenolic bobbin, typical of old small-value precision resistors. It's sleeved in some sort of plastic tube which appears to have been clear originally, but is now green over the section of wire. I'm guessing you're right and corrosion has thrown the value off. Thanks, Jonathan
On 11/13/2015 12:20 PM, Systems Glitch via vcf-midatlantic wrote:
I prefer an analog meter for troubleshooting -- like you said, easier to detect an "is it off" condition, especially with intermittent circuits. And, the loading of the analog meter can be an advantage in many situations. My Simpson 260 is always on the bench, and I keep the Simpson 160 in my toolkit since it's just the tiny version of the 260.
Same here, and the 260 is the king of 'em all. I have an HP 3458A on my bench (google it) but I end up using the 260 more, especially during calibrations. Stuff like the 3458A and other ultra-precision digital meters are great for measurement, while analog meters are much better for *adjustments*...a distinctly different application, while both involve measuring voltage. (or current, resistance..) The difference of course being that it takes less real-time brain processing to see whether a meter needle swings left or right than to read a displayed number, interpret it, decide if it's higher or lower than the last displayed number, ad infinitum. Doing that in real-time while tweaking an adjustment is a lot less efficient.
I opened it up this afternoon, it looks like the shunt for the 100 mA scale is wire (nichrome?) wrapped on a phenolic bobbin, typical of old small-value precision resistors. It's sleeved in some sort of plastic tube which appears to have been clear originally, but is now green over the section of wire. I'm guessing you're right and corrosion has thrown the value off.
The resistance wire alloy would be manganin (copper/manganese/nickel). Nichrome is rarely if ever used for actual resistors due to its very high temperature coefficient. Manganin's is negligible. You should be able to replace that with a modern resistor without trouble and get the ol' girl back up and running. Those DMMs are far from elegant, but they work very well. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
Nice HP Dave! Is the Simpson 260 still being manufactured? http://www.ebay.com/itm/381021560492 On Fri, Nov 13, 2015 at 3:22 PM, Dave McGuire via vcf-midatlantic < vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
On 11/13/2015 12:20 PM, Systems Glitch via vcf-midatlantic wrote:
I prefer an analog meter for troubleshooting -- like you said, easier to detect an "is it off" condition, especially with intermittent circuits. And, the loading of the analog meter can be an advantage in many situations. My Simpson 260 is always on the bench, and I keep the Simpson 160 in my toolkit since it's just the tiny version of the 260.
Same here, and the 260 is the king of 'em all. I have an HP 3458A on my bench (google it) but I end up using the 260 more, especially during calibrations.
Stuff like the 3458A and other ultra-precision digital meters are great for measurement, while analog meters are much better for *adjustments*...a distinctly different application, while both involve measuring voltage. (or current, resistance..) The difference of course being that it takes less real-time brain processing to see whether a meter needle swings left or right than to read a displayed number, interpret it, decide if it's higher or lower than the last displayed number, ad infinitum. Doing that in real-time while tweaking an adjustment is a lot less efficient.
I opened it up this afternoon, it looks like the shunt for the 100 mA scale is wire (nichrome?) wrapped on a phenolic bobbin, typical of old small-value precision resistors. It's sleeved in some sort of plastic tube which appears to have been clear originally, but is now green over the section of wire. I'm guessing you're right and corrosion has thrown the value off.
The resistance wire alloy would be manganin (copper/manganese/nickel). Nichrome is rarely if ever used for actual resistors due to its very high temperature coefficient. Manganin's is negligible.
You should be able to replace that with a modern resistor without trouble and get the ol' girl back up and running. Those DMMs are far from elegant, but they work very well.
-Dave
-- Dave McGuire, AK4HZ New Kensington, PA
On 11/13/2015 03:37 PM, Chris Fala via vcf-midatlantic wrote:
Nice HP Dave!
Thanks.
Is the Simpson 260 still being manufactured? http://www.ebay.com/itm/381021560492
Yes it is. -Dave -- Dave McGuire, AK4HZ New Kensington, PA
What is a fair price for a new one? This listing seems high. I imagine there are better places to buy other than eBay. This is one of those things that I always hope to get *someday*. Now that I am drooling over it, someday might just come sooner. I think my wife is in a good mood so I should seize the opportunity! LOL On Fri, Nov 13, 2015 at 3:41 PM, Dave McGuire via vcf-midatlantic < vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
On 11/13/2015 03:37 PM, Chris Fala via vcf-midatlantic wrote:
Nice HP Dave!
Thanks.
Is the Simpson 260 still being manufactured? http://www.ebay.com/itm/381021560492
Yes it is.
-Dave
-- Dave McGuire, AK4HZ New Kensington, PA
Yeah, When I was an electronics mechanic I kept a Simpson 269 on permanent check out, only surrendering it for calibration if they promised to give it back to me. 100,000 ohms/volt with a 7" mirrored scale. It was like having a calibrated eyeball with a vernier attachment. Duane -----Original Message----- From: Systems Glitch via vcf-midatlantic Sent: Friday, November 13, 2015 12:20 PM To: vcf-midatlantic@lists.vintagecomputerfederation.org Cc: Systems Glitch Subject: Re: [vcf-midatlantic] Apple IIe Voltmeter
But I found my Simpson 260 and other analog meters, put LESS load because they generally use 50uA movements (hence 20,000 ohms per volt, do the math).
Yep, one reason I don't have any non-Simpson analog meters anymore!
As to "figuring out the accuracy".....create a 10mA circuit from an accurately-measured battery and an accurately-measured resistor. Say 5V and 500 ohms, or whatever - the DVM can measure those fine, other resistors give other current sources, and math gives you the exact current. Many batteries can generally supply 10mA stable for minutes and hours or more, and your DVM can monitor their voltage anyway.
Exactly my plan. I just needed something I knew was accurate on the voltage measurement. That's the problem with two instruments you're uncertain of -- "a man with a watch always knows the time; a man with two watches is never sure!"
Why? Given the "digital is better" bias these days, only a few people call out the Simpson 260 as a valued instrument - Dave McGuire for instance, in that email list we used to use.
I prefer an analog meter for troubleshooting -- like you said, easier to detect an "is it off" condition, especially with intermittent circuits. And, the loading of the analog meter can be an advantage in many situations. My Simpson 260 is always on the bench, and I keep the Simpson 160 in my toolkit since it's just the tiny version of the 260.
Jonathan, if you determine a cause for your analog meter's apparent errors, let me know.
I opened it up this afternoon, it looks like the shunt for the 100 mA scale is wire (nichrome?) wrapped on a phenolic bobbin, typical of old small-value precision resistors. It's sleeved in some sort of plastic tube which appears to have been clear originally, but is now green over the section of wire. I'm guessing you're right and corrosion has thrown the value off. Thanks, Jonathan
Mine is a model 6P. I put in a new fuse and new battery. It works. Made an offer to an eBay seller just now for a selector knob. According to www.simpson260.com the 6P is a 1973 model. I am torn between selling it and keeping it because it was my father's. Well.... technically it still belongs to him! He gave it (and the Sencore) to me a few years ago and said I should try to sell it. :) At the time I was unable to find a buyer so they sat in the bottom drawer of my tool chest. Meanwhile a cheap Harbor Freight digital meter is the one I actually use (plenty good enough for my very basic needs). Anyway, if someone wants the 260 or the Sencore (which also works fine) then email me privately.
Why? Given the "digital is better" bias these days, only a few people call out the Simpson 260 as a valued instrument - Dave McGuire for instance, in that email list we used to use.
I've got a 260 (missing the center knob) as well as a Sencore meter. Both could use good homes. I don't know what they are worth. http://snarc.net/simpson260.jpg http://snarc.net/sencore.jpg
On Nov 13, 2015, at 11:59 AM, Herb Johnson via vcf-midatlantic <vcf-midatlantic@lists.vintagecomputerfederation.org> wrote:
I prefer analog meters when making "runs" of comparative measurements. It's easy to see if one reading is "more" or "less" than another, the needle is literally in different positions.
I prefer them for that and, for diagnosing intermediate or "wandering" problems (or quickly checking continuity), it's MUCH easier to see a needle moving than wait for the update of an LCD.
I've found variations in current measurements among several Simpson 260 meters (and among their scales) I've acquired. My guess is that some of the shunts were "cooked" by excessive current, or corroded by time and tide. I have not yet gone to the trouble of diagnosing them, I simply use the meters that have the best readings through the procedures noted. They are cheap today.
I've definitely cooked current shunts in both digital and analog meters. Nothing is immune, even the fused ones (those fuses do have a finite blow time, which is more than enough to damage something if you accidentally touch mains).
Why? Given the "digital is better" bias these days, only a few people call out the Simpson 260 as a valued instrument - Dave McGuire for instance, in that email list we used to use.
Digital is marginally better in situations where you need to record a number, but that's really just laziness. They can actually be more precise where that matters, but it seldom does. And I like the autoranging of digital meters, but that goes back to laziness. I have a very nice Fluke 87-V that I use for just about everything, but there are a lot of times I wish I had a dependable and portable analog meter as a counterpart. - Dave
participants (7)
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Chris Fala -
Dave McGuire -
David Riley -
Duane -
Evan Koblentz -
Herb Johnson -
Systems Glitch