High precision scale or balance?

I hope this is an appropriate place to ask for advice on selecting a
milligram scale or balance. It is not for jewelry, but I can't think
of any other likely forums except the ones where dabblers in
controlled substances hang out.

My cats receive several medications that must be prepared (not just
dispensed) by a pharmacist. The pharmacist's labor makes them very
expensive -- generally over $1/capsule. Our internist suggested that
I could save money by preparing some of the medications myself if I
get a scale with milligram precision. Obviously I will have no
problem getting appropriate prescriptions from him. I'm seeking advice
on how to select an appropriate scale.

Mostly I need to weigh quantities of powder from about 10 mg to 50 mg
with, say, a 10% margin of error. I will treat the scale with the
care due any precision instrument, and I will expect it to keep
working within those limits without need for maintenance or repair. I
would prefer an instrument that is small and not too heavy, as space
is limited. Naturally I don't want to spend more than necessary, but
in view of the drug costs I seek to avoid, I'm prepared to pay
hundreds of dollars if I must.

I looked on the Web and found two general types of scales that might
be appropriate.

One is an electronic jeweler's scale. Several eBay vendors are
offering them for $60-$70. Here's a URL for a typical example:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=5082080701

The other is an electronic laboratory scale. Many of these are also
advertised as jeweler's scales. They are much more expensive. A new
one will probably cost me $250-$400. An example:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7584280381

My gut tells me that the cheaper ones must be less accurate or less
reliable or both, but maybe not; maybe they just have fewer features.
Interestingly, the cheap ones seem to come with longer manufacturer's
warrantees than the expensive ones.

Comments; suggestions?

My email address is LLM041103 at earthlink dot net.

On Sat, 28 Jan 2006 16:16:42 -0800, in rec.crafts.jewelry Jonathan Sachs
wrote:

I hope this is an appropriate place to ask for advice on selecting a
milligram scale or balance. It is not for jewelry, but I can't think
of any other likely forums except the ones where dabblers in
controlled substances hang out.

you're right, it's not jewelry related as a request, but the equipment isclose
enough, so it's close enough to being appropriate... :-)

My gut tells me that the cheaper ones must be less accurate or less
reliable or both, but maybe not; maybe they just have fewer features.
Interestingly, the cheap ones seem to come with longer manufacturer's
warrantees than the expensive ones.


Mind you, I'm a jeweler, not an electronics technician. But experience with
various types of scales in the past suggests to me that you should go with your
gut feeling. The little pocket scales are convenient, but don't last as long,
nor are they always as reliable. Some are good, some are less so, especially as
they get older. It's useful to remember that although these are often sold as
carat (gem) scales, they are not actually legal for trade in that capacity,
since their margin of error is too great. They read down to the milligram
level, but are not actually accurate to that last decimal place in all too many
instances, and the user has no way of knowing if the reading is really right on,
or off by one or two. The longer warranties are perhaps indicative of the fact
that in the first place, if a fifty dollar scale goes belly up after two years,
users may be less likely to be able to even find the paperwork for warranty
work, or willing to bother with it, than they would be with a more expensive
more serious piece of equipment. And the company, getting a request for
warranty work on the cheap one, simply sends another one. The more costly
instrument might need to actually be repaired...

So it depends on just how good a scale you need and want. If your cat has only
a year to live anyway, go with the little one. If you want a better scale that
will last longer, be more consistantly accurate and reliable, get the better
one.

Just my opinion.

Sympathies for your cat(s). Been there...

Peter


Comments; suggestions?

My email address is LLM041103 at earthlink dot net.

On Sun, 29 Jan 2006 00:26:41 GMT, "Peter W.. Rowe,"
wrote:

Thanks for sharing your thoughts. They are consistent with my own
ideas as they have developed since I posted my question.

My own philosophy of choosing durable goods is to buy quality, so that
I won't have to buy twice. Thus I have pretty much ruled out the
inexpensive "diamond scales," even though your estimate of how long I
will need this instrument is, unfortunately, probably about right. I
can foresee other possible uses for a good balance; I used to dabble
in winemaking, and would like to try it again some day, and a good
balance would help.

I've tentatively decided to get an Acculab VIC-123 or VIC-303. Both
are precise to 1 mg. The 123 has a capacity of 120 g and can be
bought for about $250. The 303 has a capacity of 300 g and can be
bought for about $300. The 303 is attractive because it provides good
overlap with my postal scale (precise to 10 g), and that might come in
handy in the future.

A person in another newsgroup recommended the American Weigh Scales
MiniPro-30, which is very similar to the VIC-123 except that it is
cheaper (about $180), it has less capacity (30 g), and it optionally
runs on batteries. That is a possibility too. I'm going to see if I
can find information about the two brands' accuracy, reliability, and
general construction quality.

I did find a vendor's web site that contains some useful information
about how different types of electronic balances work, and what their
respective strong and weak points are. You may want to look at it if
you're curious about this.

http://www.adamequipment.com/am/weighing

My email address is LLM041103 at earthlink dot net.

Jonathan Sachs wrote:
I hope this is an appropriate place to ask for advice on selecting a
milligram scale or balance. It is not for jewelry, but I can't think
of any other likely forums except the ones where dabblers in
controlled substances hang out.

My cats receive several medications that must be prepared (not just
dispensed) by a pharmacist. The pharmacist's labor makes them very
expensive -- generally over $1/capsule. Our internist suggested that
I could save money by preparing some of the medications myself if I
get a scale with milligram precision. Obviously I will have no
problem getting appropriate prescriptions from him. I'm seeking advice
on how to select an appropriate scale.

Mostly I need to weigh quantities of powder from about 10 mg to 50 mg
with, say, a 10% margin of error. I will treat the scale with the
care due any precision instrument, and I will expect it to keep
working within those limits without need for maintenance or repair. I
would prefer an instrument that is small and not too heavy, as space
is limited. Naturally I don't want to spend more than necessary, but
in view of the drug costs I seek to avoid, I'm prepared to pay
hundreds of dollars if I must.

I looked on the Web and found two general types of scales that might
be appropriate.

One is an electronic jeweler's scale. Several eBay vendors are
offering them for $60-$70. Here's a URL for a typical example:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=5082080701

The other is an electronic laboratory scale. Many of these are also
advertised as jeweler's scales. They are much more expensive. A new
one will probably cost me $250-$400. An example:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7584280381

My gut tells me that the cheaper ones must be less accurate or less
reliable or both, but maybe not; maybe they just have fewer features.
Interestingly, the cheap ones seem to come with longer manufacturer's
warrantees than the expensive ones.

Comments; suggestions?

My email address is LLM041103 at earthlink dot net.



For 1 mg precision I'd go for the laboratory / scientific scales. $200
range jewelry scales would probably give 0.01 ct accuracy (2 mg) at
most, which converts to 20% error for 10 mg dose.
The scale you found on ebay seems to fit if you select the lowest
capacity model (VIC-123). You can find a better deal if you search a
bit more. (see for example:
http://www.scalesgalore.com/acculab_vicon_scales.htm ).

Is it possible to prepare several portions at once? In this case your
error becomes less significant. For example, when you use 5 mg accuracy
scale for making 10 mg dose, you have 50 % error. However, if you make
10 portions with one weighting procedure, you have 5 mg error over 100
mg medicine, namely 5% error. This will work if the drugs composition
accuracy is more important than the quantity itself taken because you
still have an error when you split the resulting mixture to portions.
You better consult your vet on that.

Sarit.
http://sarit-jewelry.com

On Sun, 29 Jan 2006 09:39:41 -0800, in rec.crafts.jewelry Jonathan Sachs
wrote:

I'm going to see if I
can find information about the two brands' accuracy, reliability, and
general construction quality.

Never heard of "american weigh" brand. But the Acculab company has been around
for quite a while, and has a fine reputation. The one's I've had have been good
instruments.

This will probably date me some, but my favorite scale, the one I trust the most
(for gems, mostly, as that the use I have that requires the greatest
resulution), I actually prefer an older non-electronic type. The Mettlerbrand
name (swiss company) was put on the map, so to speak, back in the sixties(or
fifties?) with a new design of beam balance in which the beam was totally
enclosed in the box, and the user saw a front enclosure with a weighing pan, and
dials to turn to dial in a balance weight, along with a lit scale to display the
last decimal place. The diamond scale was their H800C, calibrated in carats,
but they had lots of them in grams and milligrams too. It worked by having the
scale zeroed with a whole set of internal ring shaped weights on a rack that was
part of the beam. Turning the dials lifted successive weights off the rack to
equal the weight of your sample. Compared to earlier traditional double pan
balances, this thing was fast and easy to use, and still is, though not quite as
fast as the electronic modern ones. You had to be sure the scale was level,
(it has levelling feet and a bubble level built in), and then the accuracy
pretty much depended on maintaining the condition of the synthetic corundum
knifes on the beam. The one I've got is slightly less accurate that whenit was
made, beaing repeatable to only about a third of a point (a point is 2
milligrams), but for a forty year old balance, that's pretty good. Unlike the
electronic scales, temperature isn't an issue. No electronics to age or go out
of callibration. Totally linear. When I moved here, I had a Mettler tech come
and clean it and check the calibration and all, and I've had that done one other
time since, which showed no change. Pretty good for an almost forty yearold
scale.

The modern electronic balances are indeed quicker to use, offer lots of nice
features like multiple weighing modes, tare capabilities, and more. But unless
you're spending in the thousands, you're not quite getting total reliability, I
think. And the trouble is that with the electronics, then things are going
wrong, the scale often will still appear to be working right. I have a friend
who for a time was getting larger parcels of small diamonds in from an importer
he knew (he's a diamond setter). Using one of the small hundred buck pocket
style gem scales, he was selling off smaller lots from thse large parcelsto
other setters and jewelers. After some time, he noticed that the weight of what
he had left in the parcel didn't add up correctly. Some checking discovered
that his little scale had lost it's calibration (he'd not understood the need to
recalibrate or check the calibration). When he'd weighed out a carat of the
little stones, and charged for a carat, he'd been giving away about 1.20 worth.
A very nice discount for his customers, however many of them got this deal, and
non of whom seem to have later stepped forward to return the overage (if they
even noticed). He figures that hundred dollar scale cost him a thousand bucks
or so due to those errors. He understands now that it was, in part, his own
error in how he used the scale, since if calibrated, it then appears OK again.
But if he'd been using the old style double pan balance, this wouldn't have been
a possibility.

cheers

Peter

On Sun, 29 Jan 2006 17:39:52 GMT, "Sarit Wolfus"
wrote:

Is it possible to prepare several portions at once?

Not in the sense you mean. I do not plan to mix drugs; the whole
problem is one of sufficiently accurate measurement. I have
considered measuring a larger quantity and then dividing it into two
or four equal parts by eye. (I believe this is called quartition.)
In any case I have decided to buy a laboratory scale, so I should be
able to do the measuring either way, depending on which is more
convenient.

My email address is LLM041103 at earthlink dot net.

On Sun, 29 Jan 2006 18:00:02 GMT, "Peter W.. Rowe,"
wrote:

This will probably date me some, but my favorite scale...
a new design of beam balance in which the beam was totally
enclosed in the box, and the user saw a front enclosure with a weighing pan, and
dials to turn to dial in a balance weight, along with a lit scale to display the
last decimal place.

I used a similar instrument, probably one of theirs, in college
chemistry. That would have been 1967 or 1968. Dates me too.

I saw Mettler analytic balances in my price range on eBay. They're
readable to 0.1 mg, but they're big and complex and delicate. I
wouldn't trust one I could afford.

Pharmacists now use electronic balances with some kind of special
software that the regulatory bodies require. Typically they cost
$1500 or more. I wouldn't try to handle a drug with a low safety
margin unless I had something comparable. I'm aware of the calibration
problem (which is worse with the "inexpensive" type of laboratory
balance I'm buying), and I intend to calibrate before each use, but
for the drugs I will work with, it probably won't even matter.

Thinking ahead, I foresee one additional problem after I have measured
a tiny amount of a drug: how to get it into a gelatin capsule with an
interior diameter of about 4 mm? I wonder whether the jeweler's craft
has any techniques that might be useful. All I can think of is a tiny
funnel, but I don't know where I would find a funnel that small, or
how I would keep the powder from sticking to the walls of the funnel
or clogging the neck.

I believe pharmacists deal with this by mixing the drug with an
appropriate volume of an inactive filler and then filling each capsule
to the brim. Mixing the compounds evenly would require skills that I
don't know, and probably expensive equipment that I don't have.

My email address is LLM041103 at earthlink dot net.

Peter W.. Rowe, wrote:

The modern electronic balances are indeed quicker to use, offer lots ofnice
features like multiple weighing modes, tare capabilities, and more. But unless
you're spending in the thousands, you're not quite getting total reliability, I
think. And the trouble is that with the electronics, then things are going
wrong, the scale often will still appear to be working right.

True for most of modern technologies. One has to know the limits of a
technology in order to get the most out of it.
Load cells, in the heart of each electronic scale, are very accurate.
These sensors convert mechanical force, strain, etc. to electrical
signal, easily detectable by today's electronics. Some of these sensors
detect expansion/contraction in the deep sub-micron regime and offer an
unbeatable accuracy. However, as you say, one has to keep a standard
weight and calibrate it once in a while according to the manufacturer's
instructions.
Sarit.
http://sarit-jewelry.com

"Jonathan Sachs" wrote in message
...

Thinking ahead, I foresee one additional problem after I have measured
a tiny amount of a drug: how to get it into a gelatin capsule with an
interior diameter of about 4 mm? I wonder whether the jeweler's craft
has any techniques that might be useful. All I can think of is a tiny
funnel, but I don't know where I would find a funnel that small, or
how I would keep the powder from sticking to the walls of the funnel
or clogging the neck.

You might check your local gun shop for a small funnel. They use them to
pour gunpowder into cases for reloading.

Brian

Like many folks with more money than experience, you'll waste an
enormous bunch of money on this gadget.

Your gut is wrong, IMHO. People apply standards appropriate to the
evaluation of mechanical widgets to electronic widgets as if there were
no differences in kind. If you knew anything about digital electronics,
you'd know the limit isn't the accuracy, it's mostly the DISPLAY on
that cheaper widget which divides the looks of better stuff from
poorer. (There is no actually POOR offering in this category, I haven't
seen any systemic digital electronic failures in years in any gizmo.
Even elderly junks I pick up at flea markets are easy to return to
proper function.)

The chances are overwhelming you're solving an ego problem, not one
involving scales. Marketspeak through advertising has created an
American habit of overbuying just about everything. What is
technologically *possible* becomes what is necessary. This year's
fashion becomes the new definition of barely good enough. Last year's
ceiling is this year's floor.

The up side is that at least you'll have a good bargain to offer when
you tire of it and resell a name brand widget for someone who actually
needs an instrument he can abuse on trips galore. It should be in good
condition, given it will probably sit on your kitchen counter until the
cat dies.