Accuracy of division using MPY634

[John Fields]

On Wed, 16 Mar 2005 02:51:13 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

There is some technical content here, about 100 lines
down, where John's "flight of fancy" is controverted.

---
Hardly. What you mean is that you've posted some fluff designed to
extricate you from the position you've gotten yourself into and are
determined to try to change the focus of the argument in order to "get
the heat" off of yourself.

Good luck, but you'll have to carry on without me, since I have better
things to do with my life than proving over and over again that you're
full of shit. You're free to go.

--
John Fields

 

[Larry Brasfield]

There is some technical content here, about 100 lines
down, where John's "flight of fancy" is controverted.

"John Fields" <jfields@austininstruments.com> wrote in
message news:57ue31p1cc3mhqvm8ntj4cm0l6oo8qhnju@4ax.com...

On Tue, 15 Mar 2005 14:02:50 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:
"John Fields" <jfields@austininstruments.com> wrote in message
news:0gje31h0op11huj29vgv68hgccno91j43v@4ax.com...
On Tue, 15 Mar 2005 11:37:03 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:
[Teensy point of default agreement cut.]

The OP's schematic matches that shown in the datasheet he cited
over the caption "FIGURE 4. Basic Divider Connection". I had
noted before in this thread that his "schematic resembles it closely",
so I was surprised to see your allegation of an incorrect hookup.
---
Why? Just because you ignorantly discarded it as a possibility?

No, because, as I stated, his schematic already looked right
to me. The topology matched the diagram, no inputs were
left floating, and the output was not saturated. So my
surprise was based on information, not ignorance. Why
do you need to assume ignorance when there are much
simpler and more evident explanations?
---
In your case, ignorance _is_ the simplest explanation.

I fear we are miscommunicating here. Your
"simplest" is little more than "whatever
comes most readily to mind", motivated by
a need to feel superior. As we shall see
later, there is a simpler explanation in
the usual "Law of Parsimony" sense.

As for the "more evident" part, I am forced
to admit error on that point since it is so
dependent upon the observer's perspicacity.

Consider: A schematic drawn correctly doesn't automatically preclude
the possibility of the realization of that schematic being wired
incorrectly. Duh...
---
People hook things up backwards all the time, but I don't guess you'd
know anything about that...

Oh! Now I get it! You mean to say that not
every hand built circuit conforms to the
intended schematic at first? How could I
have missed this obvious possibility after
building engineering prototypes for years?
How wonderful to find a place where one's
betters are so willing to educate! I can
hardly express my appreciation adequately.

[Another minor point of agreement cut.]

... critic ...
---
'critique'?

But you are quite the speller, I'll give you that.
---
"Give" me that? I earned it, you pretentious ass.

Let me try that again. You have earned my
barely finite admiration as someone capable
of discovering spelling and grammar errors.

The function claimed in the spec sheet, after simplifying for the
absence of the optional summing input, is:
Vout = 10V * (Z2 - Z1) / (X1 - X2)
The OP's connection substitutes V2 for (X1-X2) and V1 for (Z2-Z1),
so the expectable result is Vout = 10V * V1 / V2. Using his numbers,
(V1=0.406V, V2=0.008V, gotVout=0.0433V, hopedVout=0.019V),
he hoped for 0.019V = 10V * 0.406 / 0.008 == 507.5, as you claim.
So, it appears that either the part manufacturer's datasheet is somewhat
fanciful, or the OP's expectation is wrong, or the hookup is wrong.
Having excluded the last, and much doubting the first, the middle way
seems worth a look.
---
"Having excluded the last" because you didn't think of it?

I excluded it because a close study of the OP's
schematic and the datasheet led me to believe
his schematic was good. And the nonsaturated
output led me to believe the inputs and power
were all actually connected to levels not far from
what correct wiring would have provided. (If
you doubt this, I can explain it in more detail.)
---
Spare me, I've already had a bellyfull of your "detail"

Having a hard time with authority, I must disobey.
Even if your education is complete, I am inclined
to make what I thought to be obvious enough more
so that you might get a glimmer of how mistaken
you have been since you elected to dump here.

From the datasheet, (eliminating the unused
summing input), the divider function is:
Vout = 10V * (Z2 - Z1) / (X1 - X2)
Substituting the signals from the OP's circuit:
Vout = 10V * V1 / V2
Now, rewriting to incorporate the input offset
that exists for each of the two inputs:
Vout = 10V * (V1 + Ezios) / (V2 + Exios)
Substituting claimed inputs and observed output,
but swapping the inputs (as discussed elsewhere):
0.0433V = 10V * (0.008V + Ezios) / (0.406V + Exios)
Solving for Ezios as a function of Exios:
Ezios = (0.0433 * Exios - 0.0624202) / 10
(If you want to see more algebra, just say so.
I am torn between your "bellyfull" lament and
your complaint about seeing too little math.)
Now, (to make this easier), suppose Exios = 0,
a value well within the typical +/- 25mV spec of
the low-grade part or the maximum +/- 20mV to 30mV
spec of the mid-grade part. This Exios value
then yields Ezios = -6.24202mV, which is also well
within the input offset spec. There are numerous
other pairs of Exios,Ezios values that could also
result in the observed Vout.

It was by means of my initial calculation, very
similar to the above, that I concluded and told
the OP: "Your results are consistent with the
input offset voltage specs for that part."

I will be interested to see if you insist upon
continuing to label this hypothesis my "'offset
error' flight of fancy" or will be willing to
acknowledge that it merits less denigration.
(My bet is placed; please do not disappoint me.)

How could I not have thought of the very possibility
that I listed?
---
You listed the possibility that the signal inputs could have been
interchanged? That's news to me...

That's clever, I guess, John. The list item at
issue was: "or the hookup is wrong". After you
suggested I did not think of "it", (referring
to that list item), I claimed that I had to think
of it to list it. Now, you are trying to change
"it"'s referrant from "the hookup is wrong" to
"the signal inputs could have been interchanged".

What point are you trying to make here? I guess
it's that it is news to you that I did something
I have neither done nor claimed to have done. I
have more news: It would be news to me as well.

It seems to me like you're
defending, tooth and nail, your position that such could not have been
the case because the schematic was drawn correctly.

My first post on this thread reflected my belief
that no wiring error was *necessary* to explain
what the OP was seeing. Contrary to what dolts
might conjecture, I have long been familiar with
the possiblity of construction errors. [1] My
position that something other than wiring error
can explain the OP's observations should not be
construed to mean that I deny the possiblity of
wiring error.

Your persistence in misconstruing my position as
"mine is the only explanation" requires you to
ignore my clear statements such as "At this point,
I think we need the OP's further input to resolve
this.", "It still could go either way.", and "I
offered it as one hypothesis."

Why do you persist, in the face of all my words
to the contrary, at leveling your scurrilous
allegation? It really makes me wonder if your
motives are so pure and admirable as you would
prefer them to be seen.

[1. I once conducted a smoke test, involving
a fixture I had designed and built, with a few
idle onlookers present. It performed in quite a
spectacular manner that had some running for the
fire extinguishers. Afterward, one of the guys
told me "Larry, please be sure to always invite
me to your smoke parties." This same device,
built more carefully the next time according to
the schematic, disappointed him but not me. So
I am well acquainted with connection errors. ]

[Some frivolity cut for space.]

The rest is blah, blah, blah, blah fucking blah.

The following quote was my effort to make sense
of what the OP wrote. If you cannot make sense
of it, I am not inclined to improve upon it for you.
---
What the OP wrote made perfect sense to me, and I was able to come to
two possible reasons for his problem without having to resort to "some
offset in the spec" explaining anything.

In other words, you neglected a hypothesis. As
truly competent folks can see, it was/is in fact
a viable hypothesis. Your notion of "having to
resort" to a hypothesis is laughable. Unless a
hypothesis is impossible or too improbable to
bother considering further, there is no reason
to treat it as something one must "resort to".

Your quote is misleading. I never wrote "some
offset in the spec" and your apparent attribution
of such silliness to me is either dishonest or a
very sloppy mistake for someone so familiar with
spelling and grammar.

There are some intriguing inferences to be
made from your misquote. If you intentionally
converted my repeated mention of "input offset
voltage" to "some offset in the spec", it means
either that you are disgustingly dishonest or
simply do not comprehend the importance of an
input offset in the 10's of mV when an input
of 8 mV is being presented. If you had actually
looked up the input offset to check my assertion,
I doubt you could honestly attempt to slight my
attention to input offset in that way. So, I am
led to conclude that you never did look at the
input offset spec since I am not convinced that
you are as dishonest as the alternative indicates.
That failure strikes me as exceedingly arrogant
and moderately comical in light of your incessant
yammering about "due diligence".

Maybe you can explain what really happened if my
above analysis omits more favorable possibilities.

If we assume the OP got his input numbers swapped and forgot to
apply the 10V scale factor, we get 0.197V = 10V * 0.008 / 0.406 .
His expected 0.019 V figure is close to the improperly scaled result.
And as I was saying, (having only looked at ratios without actually
evaluating the above related mappings), simply assuming some input
offset within the spec would explain the remaining discrepency.

Yeah, sure, and simply assuming that frogs have wings doesn't make it
so. You're full of shit Braswell, and you're grasping at straws

Do you see me claiming "This is the one and only correct
explanation for the OP's results."? I offered it as one
hypothesis. That is why I invited the OP to clarify.

To me, it looks like you are the one with some unpleasant
load to dump. It seems to occur almost daily, whether I
am the dumpee or not.
---
Yeah, you're right. I don't like bullshitters and I try to expose them
whenever I can, but maybe I'm wrong.

That is very noble of you, in a way. You
come along and cannot understand something
before it is explained in minute detail, so
you presume it must be bullshit and spend
more effort upon your dumping than you put
toward actually understanding anything.

You are way too sure that you are right as
compared to your demonstrated talent. I
suspect this is why you exhibit hateful
reactions when you perceive somebody as
putting on airs, reminding you of a trait
you dislike and would disown in yourself.

But maybe I am mistaken.

Why don't you explain this
"offset" you're talking about, quantify it, and see if there's
anywhere in the spec where:

"And as I was saying, (having only looked at ratios without actually
evaluating the above related mappings), simply assuming some input
offset within the spec would explain the remaining discrepency.

would apply?

Well, see the above starting at "From the
datasheet". Funny how your willingness to
let me explain the role of input offset has
changed so soon from "Spare me, I've already
had a bellyfull". What happened?

because you didn't spot the mistake and respond to it in your first
bullshit post, LOL!

Here, you engage in projection. You imagine my motive
based only on why you might act as you incorrectly
perceive I have acted. My mistake, if that's what it was,
lies simply in not applying the effort earlier. Perhaps
your notion of "due dilligence" makes that a mistake.
---
Finding the magic trick because of due diligence and pretending that
you would have come up with the magic trick later, even if you hadn't
been told what is was, are two quite different things.

You've got me confused here. I do not
know what "magic trick" you are going on
about. What I have come up with is my
own hypothesis as to how the OP came to
make his observations and why the output
he saw differed from what he expected,
(not to mention differing from anything
your ever predicted). I cannot imagine
who you are suggesting handed that idea
to me. It certainly was not you.

Perhaps you have confused my mention of
swapped inputs for an attempt to "take
credit" for "your" idea. What you seem
to not yet grasp is that my earliest
calculation, done before you ever piped
in, simply assumed the input arrangement
that would be needed to get what the OP
saw output rather than some 500V (which
would surely have saturated the output,
contrary to what was observed). I did
not even notice that the OP's description
had swapped (or may have swapped) those
inputs until after you had posted.

If that is the "magic trick" you accuse
me of "pretending would have come up
with", I challenge you to quote my words
to that effect. I have never thought to
attempt such a pretense, so I doubt you
can justify the notion that I did so.

At this point, I think we need the OP's further input to resolve this.
---
I'll stick with my original claim that he either wired the thing up
wrong or put the numbers in bass-ackwards, and you can stick with your
"offset error" flight of fancy, OK?

Fine. It still could go either way. However, if the
OP resolves this my way, I expect you will show
the intellectual honesty to retract that comment.
---
Expect nothing. If I'm wrong, then prove me wrong and knock of the
horseshit.

I confess to laying it on a little thickly there.
The fact is I do not expect intellectual honesty.
Thank goodness for your diligent scrutiny.

You did spot the scaling error, I'll give you that...

Generous of you.
---
I thought so.

I was jesting! I earned it! Wah!


--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

Hi all,

I'm doing a simple project which will do the voltage division,
Vo = 10(V1/V2). I do this using MPY634.

My connections are as below:

_____________________
V2 --- | X1(1) (14)+Vs|--- +15V
GND--- | X2(2) (12)Out| -----------
|SF(4) (11)Z1 |--- GND |
GND--- | Y1(6) (10)Z2 |--- V1 |
__|Y2(7) (8)-Vs |--- -15V |
| --------------------- |
|_________________________________|

The output that i got will be very inaccurate. For eg, when i pump in
V1=0.406V and V2=0.008V, the answer =0.0433V. The answer should be
0.019V. The measurements are done repeatedly and it shows consistent
results.

My circuit's connections are based on the data sheet of MPY634 at page
7 (Basic Divider Connection). You can refer to the datasheet at the
following webpage.

www.dodeca.ru/files/bb/mpy634.pdf

Does anybody know why this inaccuracy happen? Please advise.

Thanks,
Albert

 

[John Fields]

On 14 Mar 2005 19:27:04 -0800, albertleng@gmail.com wrote:

Hi all,

I'm doing a simple project which will do the voltage division,
Vo = 10(V1/V2). I do this using MPY634.

My connections are as below:

_____________________
V2 --- | X1(1) (14)+Vs|--- +15V
GND--- | X2(2) (12)Out| -----------
|SF(4) (11)Z1 |--- GND |
GND--- | Y1(6) (10)Z2 |--- V1 |
__|Y2(7) (8)-Vs |--- -15V |
| --------------------- |
|_________________________________|

The output that i got will be very inaccurate. For eg, when i pump in
V1=0.406V and V2=0.008V, the answer =0.0433V. The answer should be
0.019V. The measurements are done repeatedly and it shows consistent
results.

My circuit's connections are based on the data sheet of MPY634 at page
7 (Basic Divider Connection). You can refer to the datasheet at the
following webpage.

www.dodeca.ru/files/bb/mpy634.pdf

Does anybody know why this inaccuracy happen? Please advise.

---

They have the transfer function shown as:


10V (Z2-Z1)
Vout = ------------- + Y1
X1 - X2


so if we plug in your numbers:


10V (Z2-Z1) 10 * (0.406 - 0)
Vout = ------------- + Y1 = ------------------ + 0 = 507.5V
X1 - X2 0.008 - 0


If, however, we exchange the values of Z2 and X1 we'll have:


10 * (0.008 - 0)
Vout = ------------------ + 0 = 0.1907V
0.406 - 0


So it looks like you either have a wiring error or an error in
transcription from your V1 and V2 to their X1 and Z2.

--
John Fields

 

[Rich Grise]

On Tue, 15 Mar 2005 10:43:49 -0600, John Fields wrote:

On 14 Mar 2005 19:27:04 -0800, albertleng@gmail.com wrote:
I'm doing a simple project which will do the voltage division,
Vo = 10(V1/V2). I do this using MPY634.

_____________________
V2 --- | X1(1) (14)+Vs|--- +15V
GND--- | X2(2) (12)Out| -----------
|SF(4) (11)Z1 |--- GND |
GND--- | Y1(6) (10)Z2 |--- V1 |
__|Y2(7) (8)-Vs |--- -15V |
| --------------------- |
|_________________________________|

The output that i got will be very inaccurate. For eg, when i pump in
V1=0.406V and V2=0.008V, the answer =0.0433V. The answer should be
0.019V. The measurements are done repeatedly and it shows consistent
results.

They have the transfer function shown as:


10V (Z2-Z1)
Vout = ------------- + Y1
X1 - X2


so if we plug in your numbers:


10V (Z2-Z1) 10 * (0.406 - 0)
Vout = ------------- + Y1 = ------------------ + 0 = 507.5V
X1 - X2 0.008 - 0

I beg to differ, since it looks like in Albert's circuit, assuming Y1 and
Y2 are a differential input, that Y1 is equal to -Out, so there's some
kind of a feedback term you're neglecting, which I'm way too lazy to get
into any deeper here. And don't you have Z2 and Z1 backwards?

Thanks,
Rich

 

[John Fields]

On Tue, 15 Mar 2005 17:51:35 GMT, Rich Grise <richgrise@example.net>
wrote:

On Tue, 15 Mar 2005 10:43:49 -0600, John Fields wrote:
On 14 Mar 2005 19:27:04 -0800, albertleng@gmail.com wrote:
I'm doing a simple project which will do the voltage division,
Vo = 10(V1/V2). I do this using MPY634.

_____________________
V2 --- | X1(1) (14)+Vs|--- +15V
GND--- | X2(2) (12)Out| -----------
|SF(4) (11)Z1 |--- GND |
GND--- | Y1(6) (10)Z2 |--- V1 |
__|Y2(7) (8)-Vs |--- -15V |
| --------------------- |
|_________________________________|

The output that i got will be very inaccurate. For eg, when i pump in
V1=0.406V and V2=0.008V, the answer =0.0433V. The answer should be
0.019V. The measurements are done repeatedly and it shows consistent
results.

They have the transfer function shown as:


10V (Z2-Z1)
Vout = ------------- + Y1
X1 - X2


so if we plug in your numbers:


10V (Z2-Z1) 10 * (0.406 - 0)
Vout = ------------- + Y1 = ------------------ + 0 = 507.5V
X1 - X2 0.008 - 0


I beg to differ, since it looks like in Albert's circuit, assuming Y1 and
Y2 are a differential input, that Y1 is equal to -Out, so there's some
kind of a feedback term you're neglecting, which I'm way too lazy to get
into any deeper here. And don't you have Z2 and Z1 backwards?

---
If you're too lazy to do due diligence, then why should I bother
fucking around with you? Answer: I shouldn't. Goodbye.


--
John Fields

 

[Larry Brasfield]

"John Fields" <jfields@austininstruments.com> wrote in message
news:0gje31h0op11huj29vgv68hgccno91j43v@4ax.com...

On Tue, 15 Mar 2005 11:37:03 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:
....
Oh, gawd, are you back???

If you were paying attention, you would see that I
never went away. So, no, I am not "back".

The OP's schematic matches that shown in the datasheet he cited
over the caption "FIGURE 4. Basic Divider Connection". I had
noted before in this thread that his "schematic resembles it closely",
so I was surprised to see your allegation of an incorrect hookup.
---
Why? Just because you ignorantly discarded it as a possibility?

No, because, as I stated, his schematic already looked right
to me. The topology matched the diagram, no inputs were
left floating, and the output was not saturated. So my
surprise was based on information, not ignorance. Why
do you need to assume ignorance when there are much
simpler and more evident explanations?

People hook things up backwards all the time, but I don't guess you'd
know anything about that...

Gawd (sic), you can be obnoxious at times.

Getting to the meat of your critic, (and ignoring the hookup issue):
---
'critique'?

But you are quite the speller, I'll give you that.

The function claimed in the spec sheet, after simplifying for the
absence of the optional summing input, is:
Vout = 10V * (Z2 - Z1) / (X1 - X2)
The OP's connection substitutes V2 for (X1-X2) and V1 for (Z2-Z1),
so the expectable result is Vout = 10V * V1 / V2. Using his numbers,
(V1=0.406V, V2=0.008V, gotVout=0.0433V, hopedVout=0.019V),
he hoped for 0.019V = 10V * 0.406 / 0.008 == 507.5, as you claim.
So, it appears that either the part manufacturer's datasheet is somewhat
fanciful, or the OP's expectation is wrong, or the hookup is wrong.
Having excluded the last, and much doubting the first, the middle way
seems worth a look.

---
"Having excluded the last" because you didn't think of it?

I excluded it because a close study of the OP's
schematic and the datasheet led me to believe
his schematic was good. And the nonsaturated
output led me to believe the inputs and power
were all actually connected to levels not far from
what correct wiring would have provided. (If
you doubt this, I can explain it in more detail.)

How could I not have thought of the very possibility
that I listed? If that is intended as an insult, you
need to brush up on that skill. Otherwise, it looks
much more like hastily composed nonsense.

The rest is blah, blah, blah, blah fucking blah.

The following quote was my effort to make sense
of what the OP wrote. If you cannot make sense
of it, I am not inclined to improve upon it for you.

If we assume the OP got his input numbers swapped and forgot to
apply the 10V scale factor, we get 0.197V = 10V * 0.008 / 0.406 .
His expected 0.019 V figure is close to the improperly scaled result.
And as I was saying, (having only looked at ratios without actually
evaluating the above related mappings), simply assuming some input
offset within the spec would explain the remaining discrepency.
---
Yeah, sure, and simply assuming that frogs have wings doesn't make it
so. You're full of shit Braswell, and you're grasping at straws

Do you see me claiming "This is the one and only correct
explanation for the OP's results."? I offered it as one
hypothesis. That is why I invited the OP to clarify.

To me, it looks like you are the one with some unpleasant
load to dump. It seems to occur almost daily, whether I
am the dumpee or not.

because you didn't spot the mistake and respond to it in your first
bullshit post, LOL!

Here, you engage in projection. You imagine my motive
based only on why you might act as you incorrectly
perceive I have acted. My mistake, if that's what it was,
lies simply in not applying the effort earlier. Perhaps
your notion of "due dilligence" makes that a mistake.

At this point, I think we need the OP's further input to resolve this.
---
I'll stick with my original claim that he either wired the thing up
wrong or put the numbers in bass-ackwards, and you can stick with your
"offset error" flight of fancy, OK?

Fine. It still could go either way. However, if the
OP resolves this my way, I expect you will show
the intellectual honesty to retract that comment.

You did spot the scaling error, I'll give you that...

Generous of you.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[John Fields]

On Tue, 15 Mar 2005 14:02:50 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:0gje31h0op11huj29vgv68hgccno91j43v@4ax.com...
On Tue, 15 Mar 2005 11:37:03 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:
...
Oh, gawd, are you back???

If you were paying attention, you would see that I
never went away. So, no, I am not "back".

The OP's schematic matches that shown in the datasheet he cited
over the caption "FIGURE 4. Basic Divider Connection". I had
noted before in this thread that his "schematic resembles it closely",
so I was surprised to see your allegation of an incorrect hookup.
---
Why? Just because you ignorantly discarded it as a possibility?

No, because, as I stated, his schematic already looked right
to me. The topology matched the diagram, no inputs were
left floating, and the output was not saturated. So my
surprise was based on information, not ignorance. Why
do you need to assume ignorance when there are much
simpler and more evident explanations?

---
In your case, ignorance _is_ the simplest explanation.

Consider: A schematic drawn correctly doesn't automatically preclude
the possibility of the realization of that schematic being wired
incorrectly. Duh...
---

People hook things up backwards all the time, but I don't guess you'd
know anything about that...

Gawd (sic), you can be obnoxious at times.

---
Yes.
---

Getting to the meat of your critic, (and ignoring the hookup issue):
---
'critique'?

But you are quite the speller, I'll give you that.

---
"Give" me that? I earned it, you pretentious ass.
---

The function claimed in the spec sheet, after simplifying for the
absence of the optional summing input, is:
Vout = 10V * (Z2 - Z1) / (X1 - X2)
The OP's connection substitutes V2 for (X1-X2) and V1 for (Z2-Z1),
so the expectable result is Vout = 10V * V1 / V2. Using his numbers,
(V1=0.406V, V2=0.008V, gotVout=0.0433V, hopedVout=0.019V),
he hoped for 0.019V = 10V * 0.406 / 0.008 == 507.5, as you claim.
So, it appears that either the part manufacturer's datasheet is somewhat
fanciful, or the OP's expectation is wrong, or the hookup is wrong.
Having excluded the last, and much doubting the first, the middle way
seems worth a look.

---
"Having excluded the last" because you didn't think of it?

I excluded it because a close study of the OP's
schematic and the datasheet led me to believe
his schematic was good. And the nonsaturated
output led me to believe the inputs and power
were all actually connected to levels not far from
what correct wiring would have provided. (If
you doubt this, I can explain it in more detail.)

---
Spare me, I've already had a bellyfull of your "detail"
---

How could I not have thought of the very possibility
that I listed?

---
You listed the possibility that the signal inputs could have been
interchanged? That's news to me... It seems to me like you're
defending, tooth and nail, your position that such could not have been
the case because the schematic was drawn correctly.
---

If that is intended as an insult, you
need to brush up on that skill. Otherwise, it looks
much more like hastily composed nonsense.

---
LOL, yeah, I can see you know a _lot_ about hastily composed nonsense!
---

The rest is blah, blah, blah, blah fucking blah.

The following quote was my effort to make sense
of what the OP wrote. If you cannot make sense
of it, I am not inclined to improve upon it for you.

---
What the OP wrote made perfect sense to me, and I was able to come to
two possible reasons for his problem without having to resort to "some
offset in the spec" explaining anything.
---

If we assume the OP got his input numbers swapped and forgot to
apply the 10V scale factor, we get 0.197V = 10V * 0.008 / 0.406 .
His expected 0.019 V figure is close to the improperly scaled result.
And as I was saying, (having only looked at ratios without actually
evaluating the above related mappings), simply assuming some input
offset within the spec would explain the remaining discrepency.
---
Yeah, sure, and simply assuming that frogs have wings doesn't make it
so. You're full of shit Braswell, and you're grasping at straws

Do you see me claiming "This is the one and only correct
explanation for the OP's results."? I offered it as one
hypothesis. That is why I invited the OP to clarify.

To me, it looks like you are the one with some unpleasant
load to dump. It seems to occur almost daily, whether I
am the dumpee or not.

---
Yeah, you're right. I don't like bullshitters and I try to expose them
whenever I can, but maybe I'm wrong. Why don't you explain this
"offset" you're talking about, quantify it, and see if there's
anywhere in the spec where:

"And as I was saying, (having only looked at ratios without actually
evaluating the above related mappings), simply assuming some input
offset within the spec would explain the remaining discrepency.

would apply?
---

because you didn't spot the mistake and respond to it in your first
bullshit post, LOL!

Here, you engage in projection. You imagine my motive
based only on why you might act as you incorrectly
perceive I have acted. My mistake, if that's what it was,
lies simply in not applying the effort earlier. Perhaps
your notion of "due dilligence" makes that a mistake.

---
Finding the magic trick because of due diligence and pretending that
you would have come up with the magic trick later, even if you hadn't
been told what is was, are two quite different things.
---

At this point, I think we need the OP's further input to resolve this.
---
I'll stick with my original claim that he either wired the thing up
wrong or put the numbers in bass-ackwards, and you can stick with your
"offset error" flight of fancy, OK?

Fine. It still could go either way. However, if the
OP resolves this my way, I expect you will show
the intellectual honesty to retract that comment.

---
Expect nothing. If I'm wrong, then prove me wrong and knock of the
horseshit.
---

You did spot the scaling error, I'll give you that...

Generous of you.

---
I thought so.

--
John Fields

 

[John Fields]

On Tue, 15 Mar 2005 11:37:03 -0800, "Larry Brasfield"
<donotspam_larry_brasfield@hotmail.com> wrote:

"John Fields" <jfields@austininstruments.com> wrote in message
news:4sae315i1qb4qbmfv3giqe8fl4ogfc4v1j@4ax.com...
On Tue, 15 Mar 2005 17:51:35 GMT, Rich Grise <richgrise@example.net
wrote:

On Tue, 15 Mar 2005 10:43:49 -0600, John Fields wrote:
On 14 Mar 2005 19:27:04 -0800, albertleng@gmail.com wrote:
I'm doing a simple project which will do the voltage division,
Vo = 10(V1/V2). I do this using MPY634.

_____________________
V2 --- | X1(1) (14)+Vs|--- +15V
GND--- | X2(2) (12)Out| -----------
|SF(4) (11)Z1 |--- GND |
GND--- | Y1(6) (10)Z2 |--- V1 |
__|Y2(7) (8)-Vs |--- -15V |
| --------------------- |
|_________________________________|

The output that i got will be very inaccurate. For eg, when i pump in
V1=0.406V and V2=0.008V, the answer =0.0433V. The answer should be
0.019V. The measurements are done repeatedly and it shows consistent
results.

They have the transfer function shown as:


10V (Z2-Z1)
Vout = ------------- + Y1
X1 - X2


so if we plug in your numbers:


10V (Z2-Z1) 10 * (0.406 - 0)
Vout = ------------- + Y1 = ------------------ + 0 = 507.5V
X1 - X2 0.008 - 0


I beg to differ, since it looks like in Albert's circuit, assuming Y1 and
Y2 are a differential input, that Y1 is equal to -Out, so there's some
kind of a feedback term you're neglecting, which I'm way too lazy to get
into any deeper here. And don't you have Z2 and Z1 backwards?

---
If you're too lazy to do due diligence, then why should I bother
fucking around with you? Answer: I shouldn't. Goodbye.


I guess I'll do some diligence here, overlooking whether
it is due or not.

---
Oh, gawd, are you back???
---

The OP's schematic matches that shown in the datasheet he cited
over the caption "FIGURE 4. Basic Divider Connection". I had
noted before in this thread that his "schematic resembles it closely",
so I was surprised to see your allegation of an incorrect hookup.

---
Why? Just because you ignorantly discarded it as a possibility?
People hook things up backwards all the time, but I don't guess you'd
know anything about that...
---

Getting to the meat of your critic, (and ignoring the hookup issue):

---
'critique'?
---

The function claimed in the spec sheet, after simplifying for the
absence of the optional summing input, is:
Vout = 10V * (Z2 - Z1) / (X1 - X2)
The OP's connection substitutes V2 for (X1-X2) and V1 for (Z2-Z1),
so the expectable result is Vout = 10V * V1 / V2. Using his numbers,
(V1=0.406V, V2=0.008V, gotVout=0.0433V, hopedVout=0.019V),
he hoped for 0.019V = 10V * 0.406 / 0.008 == 507.5, as you claim.
So, it appears that either the part manufacturer's datasheet is somewhat
fanciful, or the OP's expectation is wrong, or the hookup is wrong.
Having excluded the last, and much doubting the first, the middle way
seems worth a look.

---
"Having excluded the last" because you didn't think of it?

The rest is blah, blah, blah, blah fucking blah.
---

If we assume the OP got his input numbers swapped and forgot to
apply the 10V scale factor, we get 0.197V = 10V * 0.008 / 0.406 .
His expected 0.019 V figure is close to the improperly scaled result.
And as I was saying, (having only looked at ratios without actually
evaluating the above related mappings), simply assuming some input
offset within the spec would explain the remaining discrepency.

---
Yeah, sure, and simply assuming that frogs have wings doesn't make it
so. You're full of shit Braswell, and you're grasping at straws
because you didn't spot the mistake and respond to it in your first
bullshit post, LOL!
---

At this point, I think we need the OP's further input to resolve this.

---
I'll stick with my original claim that he either wired the thing up
wrong or put the numbers in bass-ackwards, and you can stick with your
"offset error" flight of fancy, OK?

You did spot the scaling error, I'll give you that...

--
John Fields

 

[Larry Brasfield]

"John Fields" <jfields@austininstruments.com> wrote in message
news:4sae315i1qb4qbmfv3giqe8fl4ogfc4v1j@4ax.com...

On Tue, 15 Mar 2005 17:51:35 GMT, Rich Grise <richgrise@example.net
wrote:

On Tue, 15 Mar 2005 10:43:49 -0600, John Fields wrote:
On 14 Mar 2005 19:27:04 -0800, albertleng@gmail.com wrote:
I'm doing a simple project which will do the voltage division,
Vo = 10(V1/V2). I do this using MPY634.

_____________________
V2 --- | X1(1) (14)+Vs|--- +15V
GND--- | X2(2) (12)Out| -----------
|SF(4) (11)Z1 |--- GND |
GND--- | Y1(6) (10)Z2 |--- V1 |
__|Y2(7) (8)-Vs |--- -15V |
| --------------------- |
|_________________________________|

The output that i got will be very inaccurate. For eg, when i pump in
V1=0.406V and V2=0.008V, the answer =0.0433V. The answer should be
0.019V. The measurements are done repeatedly and it shows consistent
results.

They have the transfer function shown as:


10V (Z2-Z1)
Vout = ------------- + Y1
X1 - X2


so if we plug in your numbers:


10V (Z2-Z1) 10 * (0.406 - 0)
Vout = ------------- + Y1 = ------------------ + 0 = 507.5V
X1 - X2 0.008 - 0


I beg to differ, since it looks like in Albert's circuit, assuming Y1 and
Y2 are a differential input, that Y1 is equal to -Out, so there's some
kind of a feedback term you're neglecting, which I'm way too lazy to get
into any deeper here. And don't you have Z2 and Z1 backwards?

---
If you're too lazy to do due diligence, then why should I bother
fucking around with you? Answer: I shouldn't. Goodbye.

I guess I'll do some diligence here, overlooking whether
it is due or not.

The OP's schematic matches that shown in the datasheet he cited
over the caption "FIGURE 4. Basic Divider Connection". I had
noted before in this thread that his "schematic resembles it closely",
so I was surprised to see your allegation of an incorrect hookup.

Getting to the meat of your critic, (and ignoring the hookup issue):

The function claimed in the spec sheet, after simplifying for the
absence of the optional summing input, is:
Vout = 10V * (Z2 - Z1) / (X1 - X2)
The OP's connection substitutes V2 for (X1-X2) and V1 for (Z2-Z1),
so the expectable result is Vout = 10V * V1 / V2. Using his numbers,
(V1=0.406V, V2=0.008V, gotVout=0.0433V, hopedVout=0.019V),
he hoped for 0.019V = 10V * 0.406 / 0.008 == 507.5, as you claim.
So, it appears that either the part manufacturer's datasheet is somewhat
fanciful, or the OP's expectation is wrong, or the hookup is wrong.
Having excluded the last, and much doubting the first, the middle way
seems worth a look.

If we assume the OP got his input numbers swapped and forgot to
apply the 10V scale factor, we get 0.197V = 10V * 0.008 / 0.406 .
His expected 0.019 V figure is close to the improperly scaled result.
And as I was saying, (having only looked at ratios without actually
evaluating the above related mappings), simply assuming some input
offset within the spec would explain the remaining discrepency.

At this point, I think we need the OP's further input to resolve this.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.

 

[Rich Grise]

On Tue, 15 Mar 2005 11:37:03 -0800, Larry Brasfield wrote:

On 14 Mar 2005 19:27:04 -0800, albertleng@gmail.com wrote:
I'm doing a simple project which will do the voltage division,
Vo = 10(V1/V2). I do this using MPY634.

_____________________
V2 --- | X1(1) (14)+Vs|--- +15V
GND--- | X2(2) (12)Out| -----------
|SF(4) (11)Z1 |--- GND |
GND--- | Y1(6) (10)Z2 |--- V1 |
__|Y2(7) (8)-Vs |--- -15V |
| --------------------- |
|_________________________________|

The output that i got will be very inaccurate. For eg, when i pump in
V1=0.406V and V2=0.008V, the answer =0.0433V. The answer should be
0.019V. The measurements are done repeatedly and it shows consistent
results.

The function claimed in the spec sheet, after simplifying for the
absence of the optional summing input, is:
Vout = 10V * (Z2 - Z1) / (X1 - X2)

But what's that thing that looks like a line from "Out" around back to Y2?
What does the data sheet say about Y1 & Y2?

Thanks,
Rich

 

[Larry Brasfield]

"John Fields" <jfields@austininstruments.com> wrote in message
news:g75g3158h93u3v6sg1g19hnrs0p18b7dun@4ax.com...

On Wed, 16 Mar 2005 02:51:13 -0800, "Larry Brasfield"
donotspam_larry_brasfield@hotmail.com> wrote:

There is some technical content here, about 100 lines
down, where John's "flight of fancy" is controverted.
---
Hardly. What you mean is that you've posted some fluff designed to
extricate you from the position you've gotten yourself into and are
determined to try to change the focus of the argument in order to "get
the heat" off of yourself.

"fluff" == "Cannot intelligently refute".

If your inane dumps are "heat", I am not worrying, believe me.

Good luck, but you'll have to carry on without me, since I have better
things to do with my life than proving over and over again that you're
full of shit.

Thanks, buddy. You have acted true to form,
allowing me to win that bet I mentioned.

You're free to go.

Now that's pretentious.

--
--Larry Brasfield
email: donotspam_larry_brasfield@hotmail.com
Above views may belong only to me.