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--
oozing on the muggy shore of the gulf coast
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M. G. Devour wrote:
> Bob,
> We have heard that the TDS-1 tester is not the best thing to use in >
> judgeing CS and that the TDS meter is junk and doesn`t work and is a > waste
> of time and we're all *stupid* for being sucked into buying one > and
> *you've* got to try to confuse things with facts...
> Actually, I'm wondering if your "ionic current" assertion is actually
> entirely compatible with my "conductivity measurement" assertion and
> we're just quibbling over semantics?
Hi Mike, Thats right, it's semantics mostly. The TDS-1 does what it was
designed to do at a very low price, a most excellent tool. It will not
count particles, or tell how big they are, or even tell us if there is
dirt in the water. It`s not supposed to do that at all. What it does do
is tell us if there are ions in the water, which is a good indication of
mineral and metal in the water, since they usually produce ions or have
ions with them. If the water is *deionized* (distilled) there is not
supposed to be any minerals or metals or anything in the water. My
distilled water will read 001ppm which says there is not much of
anything in the water. As we run a current through the water with silver
electrodes in it some of the silver is released into the water in the
form of ions. The TDS-1 tells us these ions are there and in what
quantity. Thats all its supposed to do.
>
> I agree with you that it will only measure the charged particles, or
> ions. If you measure things like sugar that are non-polar when
> dissolved, you'll get nothing, nada, squat. Anything that's charged
> (ionic) will show up, more or less well.
>
> Well how is that different than conductivity, huh? The only reason
> something like water conducts is that there are ions in it. In the
> case of metals or semiconductors, there are free electrons or holes
> that keep the field charges from getting stuck in the lattice and
> allow current to pass through. In aqueous solutions, however, it is
> all ion transport, no?
Thats right Mike, its ionic all the way. As more ions are in the water
the conductivity will get better. The ionic reading is just another way
of stating conductivity. As we make CS more ions enter the water from
the electrodes and the conductivity gets better and the current becomes
larger and larger. Because of the low impedance of LVDC supplies the
current can run away (thats not good) and needs to be limited. On the
other hand HVAC supplies are high impedance and the current can not run
away, they don`t need current limiting.
>
> I do know that the PWT and TDS both operate on the same electronic
> principle. One of their engineers told me that much. One reads in
> ppm, the other in units of conductivity.
>
> Did you measure the voltage on the pins of the TDS in both AC and DC
> mode? With an electronic DVM, not analog?
I have taken apart one of my TDS-1`s (and put it back together again)
to see what is in it. It is a high impedance input operational amplifier
(opamp, in slang). The input is a bridge with temperature compensation
for stable ,correct reading at different water temperatures. The
temperature thermister is in the little round bump beside the two
probes. The output of the opamp is then converted into a digital display
via a ADC (analog to digital converter). The probes in contact with the
water sense the ionic potential. A current flows in the bridge which the
opamp amplifies to a usuable level for display processing. All this for
just 15 to 20 dollars, depending where you get it from.
>
> I've got an oscilloscope buried around here somewhere. It's time for
> me to see what kind of signal they're using to probe the sample. I'm
> not inclined to believe that there is some effect of ions in the
> water that can be measured passively without applying some signal.
> I guess I`m being obtuse, here, but what voltage are we talking about? > I
> just don`t see how you can get a potential to measure?
No electric voltage (potential) or ac signal is at the TDS-1 probes.
I have measured them and found nothing. The ionic potential of the water
and whats in it provides the voltage which causes a current to flow in
the input bridge. The bridge is very high imdedance and only a very
small micro current (microvoltage) in needed to cause current flow in
the bridge circuit. Well, where do we get this from in the CS?. Any time
we disassociate ions from atoms (electrons) we have a potential
(voltage) no matter how small. In a battery we disassociate them at a
fast enough rate to get a large current flow. When we don`t the battery
will be dead. The ions (electrons) will flow around the circuit trying
to equalize the potential caused by disassociation. Even in the CS we
have disassociation taking place (if we didn`t there wouldn`t be any
ions) and the small micro potential in the CS will cause a current
(microcurrent) to flow in the TDS-1 bridge.
Think of all the ions as small batteries wanting to equalize themselves
through the bridge circuit. As a matter of fact ,with the starved
current technic the water is so saturated with ions I have measured as
high as 65 millivolts in the water, just the CS, no power applied. Its
not magic, just think small. And all the TDS-1 needs is microvolts, not
millivolts which is a thousand times larger. For your money your getting
a heck of a buy. Putting a 4 inch long wire on the TDS-1 probes will
cause it to read 5ppm in the air, and when I blow on the wires the
reading changes as the ions in the air I`m blowing cause changes in the
air ionization which changes the ion flow in the TDS-1 bridge. Remember
we like negative air ions for good health, but thats another subject.
> So how would you really use the TDS-1 when you make your CS.
I take current reading every five minutes and TDS-1 reading at the same
time. I draw on paper a graph with a line for the current and a line for
the TDS-1 ppm readings. After awhile you will be able to see the
correlation of current to ppm (ions) and be able to make consistent
batches of CS time after time. I have been able to hold several charts
up to the light and see them overlay exactly for all batches.
> Thats been my belief! I like the spec`s on the PWT model, though. It`s >the
> equivalent of a 0-200 ppm TDS-1, I think. The testing range is much >better
> matched to what we are doing. Costs about forty-something bucks.
Thats a good choice, but for the money the TDS-1 can`t be beat. I have
several, and they all read the same, the agreement is pretty good.
> Mike D.
> [Mike Devour, Citizen, Patriot, Libertarian]
> [[email protected] ]
> [Speaking only for myself... ]
Bless you bob Lee
--
oozing on the muggy shore of the gulf coast
[email protected]
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