Digital Multimeters

Upside? Do you mean the sticky pointers, fragile (except for taught band meters), parallax error, sluggish response, resistive loading, accuracy specified as % of full scale, position sensitivity, marginal vibration damping, microscopic scale numbers, and no backlighting? The only advantages I can think of is that analog meters can be read quickly, and that peaking and finding a null are much easier than with a digital readout.

Weird, but there are others. Most manufacturers have at least one such (hybrid?) DMM model with an analog scale, mostly for the industrial sector. More: etc... This one gets an honorable mention:

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Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

** Been using the same budget Taut Band 20k ohms/V analogue meter for 30 years. Pretty much a copy of a Simpson as regards ranges and layout. ** Has a mirrored scale to fix that, most do.

** Auto-rangers can be slow settling.

** Not a serious issue, most high-z and amplifier circuits have unregulated PSUs anyhow with big variations in DC levels that swamp meter loading effects. Also, analog meters are not prone to large,"phantom voltage" readings due to having 11Mohms load impedance at supply frequency voltages. ** Analog meters improve their accuracy in practice by using additional 1:2:5 ranges ( 1V:2V:5V:10V ) something DMMs *simply cannot do*.

They are all restricted to using 1:10 ranges ( 2V, 20V, 200V etc) so resolution falls by a factor of 10 when nearing the lower end of a range. Hence the proliferation of 4,000, 6,000 and 20,000 count meters in recent years.

** Well, you cannot sit one on top of a speaker magnet.

** Not an inherent advantage, backlighting relies on the use of high efficiency white LEDs.

.... Phil

Well, challenging is good, but I don't know any applicable UL or IEC standard that applies to testing insulation between test instrument inputs and data port outputs. You'd have to write one up with the full knowledge that a test instrument can have a hundred inputs, and multiple data ports. You'd also have to deal with the (unknown) voltages and currents being probed, and note that a VOM STILL isn't safe if you put it onto high amps scale, touch one probe to HV, and get a finger onto the other probe.

Mainly, data ports are low voltage low current, and are tested accordingly.

Test instruments, by necessity, are flexible. Safety test requirements are not. Sometimes that means nonsensical interactions. You've found only a suitable rating for a hot-chassis instrument, NOT for a multimeter that might take a 20KV probe.

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If squirrel lets go, injury is fairly likely, and that can easily prove fat al to a wild animal. If squirrel hangs on, s/he may be able to work out how to not spin out, and thus get another regular supply of food. When you're living wild you don't turn that down. You've been outsmarted by a squirrel.

NT

Cursitor Doom wrote

You can download the source of xpsa from my site, then you will find it is written in C and compiled with gcc. I use the xforms graphics library for programs that have buttons and graphs etc, it is the fastest and best thing I have come about, and the smallest code size (apart from writing your own X11 routines).

-rwxr-xr-x 1 root root 1844127 Jul 13 2012 /usr/lib/libforms.so.1.0* Or, with your punctuation: 1,844,127 bytes, 1.8MB :-)

Much much better than all the whatsitcalled GTK Qt etc... And I have it running on raspberry too, xpsa runs on raspberry, even the very first ones, but a bit slow.

xforms (libforms) is (IMO) easy to use to make very complicated GUI programs. Even this newsreader if written using xforms.

psides of a real analogue meter.

One upside is the ability to follow varying voltages. Try doing that with a digital - there's too much delay, and the brain can't process the readout fast enough to follow. The other upside is the ability to get a very rough reading without even looking at the meter, occasionally necessary.

I don't think I've ever had a multimeter needle get sticky. Some have fet b uffered input. Most have no damping problem, that only applies to crude mov ing iron meters. All types of meter have accuracy that's a percentage of fs d plus a bit, regardless of what the manual claims. Digitals are also slugg ish otherwise they become unreadable. Etc.

NT

PS done

At least for those 2 fields. Maybe not be needed for the other ones. Will use it a while like this, se what gives.

Wrap the trunks with thin aluminum sheet available in most hardware stores for flashing around chimneys. The squirrels can't climb the trunk and canno t reach the fruit. Attach the aluminum from the bottom up using small nails so there is nothing for the squirrels to grab on to.

If there is a tree nearby they can climb and jump across to your fruit tree , then wrap that trunk as well.

The aluminum is inexpensive. It also has many other uses around the lab.

PS2 done for all (also the sub-forms)

Used setlocale(LC_NUMERIC, "");

And wrote a simple routine using isdigit() to drop anything that is not a digit from input. So you can write

123,456,789 or 123.456.789 or aa123bbb456ccc789 and the result will always be 123456789 (well it will be cut short if too long)

and displayed as 123,456,789 after processing Now for a long testing period.

I do not understand why anyone would like to hang on to all that old junk ;-)

IEC/UL (harmonized) 60950-1 covers information technology equipment (which scopes could arguably be considered one of), covers the functional-basic-reinforced insulation scheme, how much creepage/clearance is necessary, etc.

Data ports like Ethernet would be classified under one of the TNV ratings. Presumably, in-facility wiring would be rated low (SELV), but wiring between facilities could pick up induced lightning, and therefore be a higher TNV category (i.e., having hazardous transients).

So it's nice that Ethernet has 1.5kV isolation (of whatever type it happens to be rated as).

That's actually a little scary, considering Ethernet cables have exposed connections at the ends (connectors). Don't fondle the ends of long Ethernet cables during a lightning storm, and you'll probably be okay...

Right, test equipment gets a lot of sway. The assumption is that it is only operated within an environment specified by the manufacturer (i.e., in the manual), and by technicians who understand this and operate the equipment responsibly.

By very nature -- you can buy transmitters and EMP generators, in essence; these must not be illegal (well, I guess they could be licensed, but that too might be kind of over the top), because they are necessary to healthy commerce and industry.

So, it's very easy to get a CE rating on test equipment -- downside is, it's no assurance of actual emissions or susceptibility performance then.

Standards like 60950-1 are primarily concerned with safety, ensuring that, even under a single-failure condition, a user is not exposed to hazardous line voltage. What happens on the other side of the machine isn't very interesting to them, as long as it's SELV or not touchable.

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Design 
Website: https://www.seventransistorlabs.com/

Not as scary as what it replaced. 10-base-2 had exposed conductors when installed, and I've been shocked by by it. typically it was only grounded by the chain on the terminator at each end of the segment so if there was a disagreement over ground there could be tens of volts beween the BNC tee and the chassis of the PC.

--
     ?

There's no shame in admitting a squirrel got the better of you. In interactions with humans, the typical squirrel is a master-manipulator.

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That's much better now. Well done!

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Opinions on the matter seem to vary: At the height of most bird feeders, and the launch velocity of the squirrel, I would think injury would be unlikely. I've spent some quality time at a ladyfriends house, watching a resident squirrels fall off a bird feeder which has a spring loaded plate for the bird perch. The weight of the squirrel causes the plate to tip, and the squirrel to fall. My guess(tm) is the drop is about 10ft into some soft bushes. Out of hundreds of drops, I haven't seen any injured squirrels. I should make a video as one quite beautiful black squirrel will provide use with entertainment for hours. I suspect that the centrifugal squirrel launching mechanism would also not produce any injured squirrels.

Here's a video of a different squirrel that figured out that if he hangs on long enough, the battery will eventually run down: I suspect that the squirrel sensed that the motor was slowing down and that it might be advantageous to hang on until it stopped.

There's no such thing as a free lunch, unless you're a squirrel.

Drivel: Occasionally, one of the local squirrels decides to have some fun with one of the local cats. On a tree, the squirrel gets as close to the ground as possible and "scolds" the nearby cat. At some point, the cat will lunge at the squirrel and both will scurry up the tree. The squirrel is always faster than the cat, leaving the cat stuck 30 to 50ft above the ground in the tree. It usually takes hours for the cat to claw its way backwards down the tree and onto the ground. I would judge the squirrel to be smarter than the cat.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Have you noticed that we only add commas to very large strings of numbers to the right of the decimal point? Yet, we don't add commas to long strings of numbers to the left of the decimal point. Discussions on the matter don't even consider the possibility of separators to the left of the decimal point.

In the GIF file below: the center frequency readout now has commas, but just below it, the local oscillator frequency has the same number of digits, but does not include commas because most of the digits are to the left of the decimal point.

This suggests that humans only have problems decoding large numbers, but not small numbers, or consider small numbers to be unworthy of including separators.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558

Oddly, Digital Equipment Comany (while they were around) actually had insulated

10base2 connections all worked out; it'd be safe to handle except when a wiring change was being made. Some similar things are still available

Thankfully, in a building fitted with half-inch copper bars welded to ground cables, we never got a shock due to the shields. 10base2 was pretty scarce by the end of last century.

** Needles hitting end stops hard makes a sharp sound in a quiet workshop - a simple warning that DMMs never supply. Since diode protection of movemen ts became standard ( c 1970 ) you do not have to worry about the sub 1mW co il dissipation involved.

The first person I recommended buy himself a DMM to replace his aging analo g owned a live sound business. I pointed out advantages like being almost a buse proof: you could drop one repeatedly with no harm and even unintention ally probe the AC supply using an ohms range without fear - two big killers of analog multimeters.

Next time I saw him, he was grumpy how his new meter showed an unreadable d isplay when connected to a loudspeaker system while his old meter worked fi ne.

He was perfectly correct, the X1 ohms range of an analog meter works at muc h higher current than the X1 range of a DMM ( c 50mA v

Actually grounded at one end only. Having other ground contacts, such as a BNC connector touching a grounded structure and he segment might not work. The ground potential difference between equipment fed from different feeders can be quite significant in normal situations, so galvanic isolation of data connections (including Ethernet) is critical.

When two buildings with separate feeds and separate grounding electrodes are connected together, there can be hundreds of kilovolts potential difference, when a lightning hits one building only. Clearly ordinary galvanic isolation doesn't survive such transients, only optical fiber connections will work even during such lightning hits.

surely it's earthed at every PC it's plugged into. I don't recall any bare conductors either, unless an end was unterminated.

NT