Error of % + digits?...

[Cydrome Leader]

In sci.electronics.basics Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <rd400g$egj$2@reader1.panix.com>, presence@MUNGEpanix.com
says...

So the object was precision and not accuracy.

If the goal was keep the needle on their marks it does\'t have to mean
anything was precise. Maybe your guages had no faces, or read mA instead
of degrees, and bent needles. As long as your +/- 3 degree thermocouples
and controllers did not jump up and down + and then -3 degrees all the
time, you were good.



One good example of what we had is this.

In a vat of material is a test hole. In that hole is a rod about 3/8
inch in diameter and a foot long. At the end there are two
thermocouples and two RTDs. The thermocouples wires go about 100 feet
to a PLC (similar to a computer) card that converts the milivolts to
digital that is then displayed on a compute screen. The RTDs go about
10 feet to a converter that converts the change in resistance to a 4 to
20 miliamp signal. That goes to a card on the PLC and then to the
computer display.

While the computer will display to 3 decimal places at 300 deg C from
the lowest to the highest temperature shown on the display can be around
3 deg differnet and all 3 be within the limits of the equipmnet.

At a certain time a sample is sent to the lab and one of the computer
displays is set as a standard and the object of the PLC is to keep the
actual temperature , whatever it actually is, to that \'standard\'. Not
too accurate as to temperature, but very precice. The operators only
needed to keep that one computer display as close to that \'mark\' as they
can if for some reason the PLC messes up and they have to adjust the
control manual.

What\'s the control loop if the PLC dies? How do people control temperatures
manually? Is there a foot pedal to stomp on to switch the heaters on and
off?


There\'s a couple machines I fuss with that use platinum junction RTDs and
we have alarm limits set. If the machine drifts into an alarm state,
outside of a warmup period that\'s pretty much the end of the day and
everything stops until it can be fixed. The loops on these machines are
tuned to maintain and hold a set point of less than 1 degree F. The
displays are all wrong, show fake levels of precision, and read in C, but
are wrong by several degrees, even if you do the math. We gave up trying to
calibrate the displays against what the real temperature with the offset
features when the probes were last changed. It just isn\'t worth the time.
Those machines are not accurate, they\'re not precise (as measured with
their own instrumentation), but they will absolutely hold a stable
temperature if you can determine the set points yourself.

 

[Cydrome Leader]

In sci.electronics.basics Pimpom <nobody@nowhere.com> wrote:

On 6/26/2020 9:53 AM, Cydrome Leader wrote:
In sci.electronics.equipment Pimpom <nobody@nowhere.com> wrote:

My mechanical slide caliper has a resolution of 0.001 inch. This
means that it can display measurements with a precision of 1 mil,

What if your caliper had a resolution of 1 mil +/- 3 counts on the last
digit? That\'s the issue with multimeters that have completely bogus digits
at the end. Those number are just noise and serve no purpose at all. They
don\'t even compare to all bullets missing the target but landing in the
same wrong spot.

You seem intent on picking an argument by inserting a statement
that agrees with the following sentences. BTW, my caliper is not
digital, so the matter of +/- count is irrelevant.

electronic test equipment is digital these days, so my question is very
valid.

How would you feel if your vernier or thimble readouts on your hand tools
had number that randomly moved around? That\'s the goofiness of how these
digital integrating meters work. It makes very little sense when directly
translated into the physical word.

Take a 100 foot surveyor\'s tape measure. Those are simple to read. You have
feet and inches, and they\'re all in order. Let\'s our 100 foot tape is
accurate to 3inches over that 100 feet. Not great, but fine for us.

Now go digital, with the analog feel. Say the tape is now a long e-ink
display and has no factory printed numers on it like a conventional tape.
Every time you pull the tape out it redisplays tape measure printing and
you get stuff like this:

.... 12ft 1in 2in 4in 5in 3in 6in 7in 8in 9in 11in 10in 13ft ...

How would that feel?

It makes absolutely no sense unless you understand the silly types of
errors that are display on devices where we expect direct read out of
numbers.

but that doesn\'t guarantee that a measurement taken with it will
be accurate to 1 mil. I may not always press the jaws snugly
enough and the scale may not be perfectly accurate.

crappy meters can lack \"snug\" readings.

 

[Cydrome Leader]

In sci.electronics.basics Pimpom <nobody@nowhere.com> wrote:

On 6/26/2020 9:53 AM, Cydrome Leader wrote:
In sci.electronics.equipment Pimpom <nobody@nowhere.com> wrote:

My mechanical slide caliper has a resolution of 0.001 inch. This
means that it can display measurements with a precision of 1 mil,

What if your caliper had a resolution of 1 mil +/- 3 counts on the last
digit? That\'s the issue with multimeters that have completely bogus digits
at the end. Those number are just noise and serve no purpose at all. They
don\'t even compare to all bullets missing the target but landing in the
same wrong spot.

You seem intent on picking an argument by inserting a statement
that agrees with the following sentences. BTW, my caliper is not
digital, so the matter of +/- count is irrelevant.

electronic test equipment is digital these days, so my question is very
valid.

How would you feel if your vernier or thimble readouts on your hand tools
had number that randomly moved around? That\'s the goofiness of how these
digital integrating meters work. It makes very little sense when directly
translated into the physical word.

Take a 100 foot surveyor\'s tape measure. Those are simple to read. You have
feet and inches, and they\'re all in order. Let\'s our 100 foot tape is
accurate to 3inches over that 100 feet. Not great, but fine for us.

Now go digital, with the analog feel. Say the tape is now a long e-ink
display and has no factory printed numers on it like a conventional tape.
Every time you pull the tape out it redisplays tape measure printing and
you get stuff like this:

.... 12ft 1in 2in 4in 5in 3in 6in 7in 8in 9in 11in 10in 13ft ...

How would that feel?

It makes absolutely no sense unless you understand the silly types of
errors that are display on devices where we expect direct read out of
numbers.

but that doesn\'t guarantee that a measurement taken with it will
be accurate to 1 mil. I may not always press the jaws snugly
enough and the scale may not be perfectly accurate.

crappy meters can lack \"snug\" readings.

 

[Ralph Mowery]

In article <rd6pl5$42t$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

What\'s the control loop if the PLC dies? How do people control temperatures
manually? Is there a foot pedal to stomp on to switch the heaters on and
off?

The process has two PLCs running all the time. There are two or more
computers hooked to the data stream for the PLCs One PLC is the so
called hot backup. It is not controlling, but if the primary one quits,
the secondary one will either switch over automatically or it can be
manually switched.

One thermocouple is connected to the control loop. If that TC goes bad,
there are other TCs that give the temperature readout and the operators
switch the control screen for that temperature to manual and they have
to keep an eye on it and manually enter on the computer keyboard what
percentage of valve opening is needed to mantain the correct
temperature.

 

[Ralph Mowery]

In article <rd6pl5$42t$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

What\'s the control loop if the PLC dies? How do people control temperatures
manually? Is there a foot pedal to stomp on to switch the heaters on and
off?

The process has two PLCs running all the time. There are two or more
computers hooked to the data stream for the PLCs One PLC is the so
called hot backup. It is not controlling, but if the primary one quits,
the secondary one will either switch over automatically or it can be
manually switched.

One thermocouple is connected to the control loop. If that TC goes bad,
there are other TCs that give the temperature readout and the operators
switch the control screen for that temperature to manual and they have
to keep an eye on it and manually enter on the computer keyboard what
percentage of valve opening is needed to mantain the correct
temperature.

 

[Cydrome Leader]

In sci.electronics.basics Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <rd6pl5$42t$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

What\'s the control loop if the PLC dies? How do people control temperatures
manually? Is there a foot pedal to stomp on to switch the heaters on and
off?




The process has two PLCs running all the time. There are two or more
computers hooked to the data stream for the PLCs One PLC is the so
called hot backup. It is not controlling, but if the primary one quits,
the secondary one will either switch over automatically or it can be
manually switched.

One thermocouple is connected to the control loop. If that TC goes bad,
there are other TCs that give the temperature readout and the operators
switch the control screen for that temperature to manual and they have
to keep an eye on it and manually enter on the computer keyboard what
percentage of valve opening is needed to mantain the correct
temperature.

OK, so if a PLC croaks, the operators can switch to the redundant one. If a
probe of whatever you have between it and the current loop or whatever it
was fails, it\'s 100% manual control? How do you share the reading from one
problem? Not trying to pole holes in theory here, just actually curious.

One thing annoying about the probes I deal with is it seems no two are
alike. Never been able to swap one for another, even with short leads, even
with three lead compensation and get the same behavior on the same
controller.

 

[Cydrome Leader]

In sci.electronics.basics Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <rd6pl5$42t$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

What\'s the control loop if the PLC dies? How do people control temperatures
manually? Is there a foot pedal to stomp on to switch the heaters on and
off?




The process has two PLCs running all the time. There are two or more
computers hooked to the data stream for the PLCs One PLC is the so
called hot backup. It is not controlling, but if the primary one quits,
the secondary one will either switch over automatically or it can be
manually switched.

One thermocouple is connected to the control loop. If that TC goes bad,
there are other TCs that give the temperature readout and the operators
switch the control screen for that temperature to manual and they have
to keep an eye on it and manually enter on the computer keyboard what
percentage of valve opening is needed to mantain the correct
temperature.

OK, so if a PLC croaks, the operators can switch to the redundant one. If a
probe of whatever you have between it and the current loop or whatever it
was fails, it\'s 100% manual control? How do you share the reading from one
problem? Not trying to pole holes in theory here, just actually curious.

One thing annoying about the probes I deal with is it seems no two are
alike. Never been able to swap one for another, even with short leads, even
with three lead compensation and get the same behavior on the same
controller.

 

[Ralph Mowery]

In article <rdblel$f8m$5@reader1.panix.com>, presence@MUNGEpanix.com
says...

OK, so if a PLC croaks, the operators can switch to the redundant one. If a
probe of whatever you have between it and the current loop or whatever it
was fails, it\'s 100% manual control? How do you share the reading from one
problem? Not trying to pole holes in theory here, just actually curious.

One thing annoying about the probes I deal with is it seems no two are
alike. Never been able to swap one for another, even with short leads, even
with three lead compensation and get the same behavior on the same
controller.

Here is sort of how it works. One PLC quits. The second PLC takes over
automatically or can be switched manually at any time.


A TC feeding the PLCs fails. An alarm is sounded as the PLC thinks the
process has gone out of limits. The operator is at a computer (was
running a graphics program on Win XP when I left) , He calls up the
control screen and puts the control in manual and sets the signal to the
valve to where it was before the device fails. There is a secondary
temperature TC. The operator looks back in the history of the read outs
and sees that the primary control TC was showing 300.2 deg C when the
lab said the process was on target. At the same time the secondary TC
was showing 301.6 deg C. So the operator now has the control in manual
and adjusts the output of the contoler to try and keep the process at
301.6 deg C showing on the readiout now.

When the bad TC is replaced and the process is checked out by the lab,
The new setting may come back as 301.1 deg C. So that will be the new
target.

The vessels are large enough , around 10 feet tall and 5 feet in
diameter so the temperature change takes a long time.

The process is making polyester material. We put in a powder that looks
like flour and a liquid Glycol. It is heated to about 300 deg C. There
are 5 vessels in the process and it is continious. The powder and
liquid are put in the first vessel and at the bottom is a pipe that
conveys it to the next one. The process is repeated and small ammouts
of other chemicals are added at each stage. It is extruded after the
last vessel to what looks like string.
It takes about 15 hours for the material to make it from start to
finish. We make about 3000 pounds to 10,000 pounds of material each
hour depending on the size of the process line.

About 2 years ago the plant that had around 3000 people 20 years ago
went out of business. Mostly because of other countries makeing the
material much cheaper.

 

[Commander Kinsey]

On Wed, 24 Jun 2020 21:06:04 +0100, Rich <rich@example.invalid> wrote:

In sci.electronics.equipment Commander Kinsey <CFKinsey@military.org.jp> wrote:
On Thu, 18 Jun 2020 15:38:46 +0100, Pimpom <nobody@nowhere.com> wrote:

On 6/18/2020 6:33 PM, Commander Kinsey wrote:
I just bought an amp clamp meter, and it states the error is \"+/-
1.9% + 3 digits\". What does the \"3 digits\" part mean?


If your meter should read, say 1.875 A, the correct reading could
be anywhere from 1.872 to 1.878. This is a possible error in the
display presented to you in the analog-digital display conversion
process. The +/-1.9% possible error is about the measurement
taken including - but not only - any error made by the sensor.

Thanks, I wonder why all my other meters only list a % error. Is it
included within it somehow, or are they just lying, or do some meters
not have this error?

One generally finds the percentage plus digits error measures on more
expensive equipment. Less expensive equipment more often than not only
lists a percentage and nothing more.

So should I assume the cheaper ones are lying? Or have they just made a rough estimate adding the two errors?

 

[Cydrome Leader]

In sci.electronics.equipment Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <rdblel$f8m$5@reader1.panix.com>, presence@MUNGEpanix.com
says...

OK, so if a PLC croaks, the operators can switch to the redundant one. If a
probe of whatever you have between it and the current loop or whatever it
was fails, it\'s 100% manual control? How do you share the reading from one
problem? Not trying to pole holes in theory here, just actually curious.

One thing annoying about the probes I deal with is it seems no two are
alike. Never been able to swap one for another, even with short leads, even
with three lead compensation and get the same behavior on the same
controller.



Here is sort of how it works. One PLC quits. The second PLC takes over
automatically or can be switched manually at any time.


A TC feeding the PLCs fails. An alarm is sounded as the PLC thinks the
process has gone out of limits. The operator is at a computer (was
running a graphics program on Win XP when I left) , He calls up the
control screen and puts the control in manual and sets the signal to the
valve to where it was before the device fails. There is a secondary
temperature TC. The operator looks back in the history of the read outs
and sees that the primary control TC was showing 300.2 deg C when the
lab said the process was on target. At the same time the secondary TC
was showing 301.6 deg C. So the operator now has the control in manual
and adjusts the output of the contoler to try and keep the process at
301.6 deg C showing on the readiout now.

When the bad TC is replaced and the process is checked out by the lab,
The new setting may come back as 301.1 deg C. So that will be the new
target.

The vessels are large enough , around 10 feet tall and 5 feet in
diameter so the temperature change takes a long time.

The process is making polyester material. We put in a powder that looks
like flour and a liquid Glycol. It is heated to about 300 deg C. There
are 5 vessels in the process and it is continious. The powder and
liquid are put in the first vessel and at the bottom is a pipe that
conveys it to the next one. The process is repeated and small ammouts
of other chemicals are added at each stage. It is extruded after the
last vessel to what looks like string.
It takes about 15 hours for the material to make it from start to
finish. We make about 3000 pounds to 10,000 pounds of material each
hour depending on the size of the process line.

About 2 years ago the plant that had around 3000 people 20 years ago
went out of business. Mostly because of other countries makeing the
material much cheaper.

Interesting.

I met an engineer who worked at Eastman decades ago. He had good stories
about the complexity of starting a new production line of chemicals or
plastics whatever they were making at the time. The amusing part was none
of the people that designed the new systems could never get the first
batches to work at full scale. They\'d have an old timer operator figure it
out for them after they all gave up. This process could take days.

The final \"say\" on the machines I deal with are the colors of test strips
that run through the entire process.

 

[Cydrome Leader]

In sci.electronics.equipment Commander Kinsey <CFKinsey@military.org.jp> wrote:

On Wed, 24 Jun 2020 21:06:04 +0100, Rich <rich@example.invalid> wrote:

In sci.electronics.equipment Commander Kinsey <CFKinsey@military.org.jp> wrote:
On Thu, 18 Jun 2020 15:38:46 +0100, Pimpom <nobody@nowhere.com> wrote:

On 6/18/2020 6:33 PM, Commander Kinsey wrote:
I just bought an amp clamp meter, and it states the error is \"+/-
1.9% + 3 digits\". What does the \"3 digits\" part mean?


If your meter should read, say 1.875 A, the correct reading could
be anywhere from 1.872 to 1.878. This is a possible error in the
display presented to you in the analog-digital display conversion
process. The +/-1.9% possible error is about the measurement
taken including - but not only - any error made by the sensor.

Thanks, I wonder why all my other meters only list a % error. Is it
included within it somehow, or are they just lying, or do some meters
not have this error?

One generally finds the percentage plus digits error measures on more
expensive equipment. Less expensive equipment more often than not only
lists a percentage and nothing more.

So should I assume the cheaper ones are lying? Or have they just made a rough estimate adding the two errors?

might be both. I dug out my first DMM, a Wavetek DM2, circa 1990s. It might
have been from a raffle or something like that.

The DC voltage specs range from 0.8% +1 digit (not bad really) over to the
AC ranges which are \"1.2% RDG +10 Digits\". If I had new leads, I\'d trust it
with outlet voltage, but would stay away from 208volts. The meter has 3.5
digits or max display of 1999. I\'m figuring a real 100volt AC reading could
be 99 to 101 plus another error of +/- 1 volt for the 10 digits tolerance
on the display or count. so 100volts from your Japanese outlet reference
might read 98 to 102 volts. So while in the ballpark, it\'s better than you
can read off a Simpson 260 meter in the AC voltage range. I could be wrong
on this too.

It\'s a pretty decent meter for poking at DC circuits for the tens of
dollars is must have cost when new.

 

[Rich]

In sci.electronics.equipment Commander Kinsey <CFKinsey@military.org.jp> wrote:

On Wed, 24 Jun 2020 21:06:04 +0100, Rich <rich@example.invalid> wrote:

In sci.electronics.equipment Commander Kinsey <CFKinsey@military.org.jp> wrote:
On Thu, 18 Jun 2020 15:38:46 +0100, Pimpom <nobody@nowhere.com> wrote:

On 6/18/2020 6:33 PM, Commander Kinsey wrote:
I just bought an amp clamp meter, and it states the error is \"+/-
1.9% + 3 digits\". What does the \"3 digits\" part mean?


If your meter should read, say 1.875 A, the correct reading could
be anywhere from 1.872 to 1.878. This is a possible error in the
display presented to you in the analog-digital display conversion
process. The +/-1.9% possible error is about the measurement
taken including - but not only - any error made by the sensor.

Thanks, I wonder why all my other meters only list a % error. Is
it included within it somehow, or are they just lying, or do some
meters not have this error?

One generally finds the percentage plus digits error measures on
more expensive equipment. Less expensive equipment more often than
not only lists a percentage and nothing more.

So should I assume the cheaper ones are lying?

More likely they simply invested less effort in measuring their
respective meters accuracy. And a generally safe assumption is that
lower cost often equates to less accurate.

> Or have they just made a rough estimate adding the two errors?

This is likely, but without being able to ask the maker, anything we
surmise here is just a guess anyway.

 

[Ralph Mowery]

In article <rdecuc$m73$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

So should I assume the cheaper ones are lying? Or have they just made a rough estimate adding the two errors?

might be both. I dug out my first DMM, a Wavetek DM2, circa 1990s. It might
have been from a raffle or something like that.

The DC voltage specs range from 0.8% +1 digit (not bad really) over to the
AC ranges which are \"1.2% RDG +10 Digits\". If I had new leads, I\'d trust it
with outlet voltage, but would stay away from 208volts. The meter has 3.5
digits or max display of 1999. I\'m figuring a real 100volt AC reading could
be 99 to 101 plus another error of +/- 1 volt for the 10 digits tolerance
on the display or count. so 100volts from your Japanese outlet reference
might read 98 to 102 volts. So while in the ballpark, it\'s better than you
can read off a Simpson 260 meter in the AC voltage range. I could be wrong
on this too.

It\'s a pretty decent meter for poking at DC circuits for the tens of
dollars is must have cost when new.

It seems that maybe due to modern manufactoring the meters are more
accurate than they were 20 years ago. I bought some DC voltmeters from
China. They display 3 digits. They read from 0 to 99.9 volts. I coulg
get 4 of them for less than $ 15 including the shipping. I hooked all 4
of them in parallel with a Fluke 87 . Three of them tracked right along
with the Fluke with the last digit sometimes being one high or low from
0 to 24 volts. The fourth one was off by an average of 2 on the last
digit. I found an adjustment screw on the back of the meter and tweaked
it and re ran the test. It then fell in line with the other meters.

I had 3 or 4 of the Harbor Freight \'free\' multimeters. The ones that
usually sell for around $ 5. They seem to be reasonable accurate for
the money. Plenty accurate for the home user to test things around the
house. I do admit that the safety issue of putting them across the 120
or 240 volt power wires is somewhat doubtful. I sure would not use one
where I worked to put across the 480 volt 3 phase system that is fused
with 200 amps.

 

[Cydrome Leader]

In sci.electronics.equipment Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <rdecuc$m73$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

So should I assume the cheaper ones are lying? Or have they just made a rough estimate adding the two errors?

might be both. I dug out my first DMM, a Wavetek DM2, circa 1990s. It might
have been from a raffle or something like that.

The DC voltage specs range from 0.8% +1 digit (not bad really) over to the
AC ranges which are \"1.2% RDG +10 Digits\". If I had new leads, I\'d trust it
with outlet voltage, but would stay away from 208volts. The meter has 3.5
digits or max display of 1999. I\'m figuring a real 100volt AC reading could
be 99 to 101 plus another error of +/- 1 volt for the 10 digits tolerance
on the display or count. so 100volts from your Japanese outlet reference
might read 98 to 102 volts. So while in the ballpark, it\'s better than you
can read off a Simpson 260 meter in the AC voltage range. I could be wrong
on this too.

It\'s a pretty decent meter for poking at DC circuits for the tens of
dollars is must have cost when new.



It seems that maybe due to modern manufactoring the meters are more
accurate than they were 20 years ago. I bought some DC voltmeters from
China. They display 3 digits. They read from 0 to 99.9 volts. I coulg
get 4 of them for less than $ 15 including the shipping. I hooked all 4
of them in parallel with a Fluke 87 . Three of them tracked right along
with the Fluke with the last digit sometimes being one high or low from
0 to 24 volts. The fourth one was off by an average of 2 on the last
digit. I found an adjustment screw on the back of the meter and tweaked
it and re ran the test. It then fell in line with the other meters.

Have you run this test with AC? That seems to be where the wheels come
off. I brought up this thread to a friend and he mentioned his quest to
repair some sort of HP true RMS meter that uses a thermocouple and heater
to properly measure complex waveforms. I can\'t even guess how slow such a
meter might be.

I had 3 or 4 of the Harbor Freight \'free\' multimeters. The ones that
usually sell for around $ 5. They seem to be reasonable accurate for
the money. Plenty accurate for the home user to test things around the
house. I do admit that the safety issue of putting them across the 120
or 240 volt power wires is somewhat doubtful. I sure would not use one
where I worked to put across the 480 volt 3 phase system that is fused
with 200 amps.

I\'m pretty timid with anything upstream from a plain outlet. I had an
edison base fuse burst in my hand once. Never seen one come apart before.
It was just a 120v lighting circuit, but right off the service panel.
There\'s way more excitement near those things.

 

[Jasen Betts]

On 2020-07-02, Cydrome Leader <presence@MUNGEpanix.com> wrote:

In sci.electronics.equipment Ralph Mowery <rmowery28146@earthlink.net> wrote:
In article <rdecuc$m73$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

So should I assume the cheaper ones are lying? Or have they just made a rough estimate adding the two errors?

might be both. I dug out my first DMM, a Wavetek DM2, circa 1990s. It might
have been from a raffle or something like that.

The DC voltage specs range from 0.8% +1 digit (not bad really) over to the
AC ranges which are \"1.2% RDG +10 Digits\". If I had new leads, I\'d trust it
with outlet voltage, but would stay away from 208volts. The meter has 3.5
digits or max display of 1999. I\'m figuring a real 100volt AC reading could
be 99 to 101 plus another error of +/- 1 volt for the 10 digits tolerance
on the display or count. so 100volts from your Japanese outlet reference
might read 98 to 102 volts. So while in the ballpark, it\'s better than you
can read off a Simpson 260 meter in the AC voltage range. I could be wrong
on this too.

It\'s a pretty decent meter for poking at DC circuits for the tens of
dollars is must have cost when new.



It seems that maybe due to modern manufactoring the meters are more
accurate than they were 20 years ago. I bought some DC voltmeters from
China. They display 3 digits. They read from 0 to 99.9 volts. I coulg
get 4 of them for less than $ 15 including the shipping. I hooked all 4
of them in parallel with a Fluke 87 . Three of them tracked right along
with the Fluke with the last digit sometimes being one high or low from
0 to 24 volts. The fourth one was off by an average of 2 on the last
digit. I found an adjustment screw on the back of the meter and tweaked
it and re ran the test. It then fell in line with the other meters.

Have you run this test with AC? That seems to be where the wheels come
off. I brought up this thread to a friend and he mentioned his quest to
repair some sort of HP true RMS meter that uses a thermocouple and heater
to properly measure complex waveforms. I can\'t even guess how slow such a
meter might be.

The heaters used in thermal printers manage a speed better than 10mS
stuff done in a microchip (like LT1088) could be even faster.

--
Jasen.

 

[Ralph Mowery]

In article <rdjsa6$28b$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

Have you run this test with AC? That seems to be where the wheels come
off. I brought up this thread to a friend and he mentioned his quest to
repair some sort of HP true RMS meter that uses a thermocouple and heater
to properly measure complex waveforms. I can\'t even guess how slow such a
meter might be.

I had 3 or 4 of the Harbor Freight \'free\' multimeters. The ones that
usually sell for around $ 5. They seem to be reasonable accurate for
the money. Plenty accurate for the home user to test things around the
house. I do admit that the safety issue of putting them across the 120
or 240 volt power wires is somewhat doubtful. I sure would not use one
where I worked to put across the 480 volt 3 phase system that is fused
with 200 amps.

I\'m pretty timid with anything upstream from a plain outlet. I had an
edison base fuse burst in my hand once. Never seen one come apart before.
It was just a 120v lighting circuit, but right off the service panel.
There\'s way more excitement near those things.

I have not ran any tests for AC . The things I work with don\'t care
about very much about being accurate to more than around 5 %. Usually
it is more of do I have a voltage/current or not.

When I work on most anything other than low voltage (below 100 volts) I
ues either my Simpson 260 analog meter or a Fluke meter that is rated
for cat 3 and 4. If you have not heard of the Cat numbers, they are for
devices used in different power circuits. I don\'t know the numbers off
hand, but it goes something like this, Cat 1 is for low voltage items,
Cat 2 for things like stoves and refrigerators, Cat 3 for homw
wiring,and Cat 4 for the very high power circuits like I often worked on
like the 480 volt AC and 300 amps.

For a real scare you should see some of the safety movies that Fluke put
out. They show under test conditions what can hapen to inexpensive
meters and their meters under different conditions like having the
meter set for amps and putting across a 480 volt circuit that has plenty
of amps .

 

[Ralph Mowery]

In article <rdblel$f8m$5@reader1.panix.com>, presence@MUNGEpanix.com
says...

OK, so if a PLC croaks, the operators can switch to the redundant one. If a
probe of whatever you have between it and the current loop or whatever it
was fails, it\'s 100% manual control? How do you share the reading from one
problem? Not trying to pole holes in theory here, just actually curious.

One thing annoying about the probes I deal with is it seems no two are
alike. Never been able to swap one for another, even with short leads, even
with three lead compensation and get the same behavior on the same
controller.

Here is sort of how it works. One PLC quits. The second PLC takes over
automatically or can be switched manually at any time.


A TC feeding the PLCs fails. An alarm is sounded as the PLC thinks the
process has gone out of limits. The operator is at a computer (was
running a graphics program on Win XP when I left) , He calls up the
control screen and puts the control in manual and sets the signal to the
valve to where it was before the device fails. There is a secondary
temperature TC. The operator looks back in the history of the read outs
and sees that the primary control TC was showing 300.2 deg C when the
lab said the process was on target. At the same time the secondary TC
was showing 301.6 deg C. So the operator now has the control in manual
and adjusts the output of the contoler to try and keep the process at
301.6 deg C showing on the readiout now.

When the bad TC is replaced and the process is checked out by the lab,
The new setting may come back as 301.1 deg C. So that will be the new
target.

The vessels are large enough , around 10 feet tall and 5 feet in
diameter so the temperature change takes a long time.

The process is making polyester material. We put in a powder that looks
like flour and a liquid Glycol. It is heated to about 300 deg C. There
are 5 vessels in the process and it is continious. The powder and
liquid are put in the first vessel and at the bottom is a pipe that
conveys it to the next one. The process is repeated and small ammouts
of other chemicals are added at each stage. It is extruded after the
last vessel to what looks like string.
It takes about 15 hours for the material to make it from start to
finish. We make about 3000 pounds to 10,000 pounds of material each
hour depending on the size of the process line.

About 2 years ago the plant that had around 3000 people 20 years ago
went out of business. Mostly because of other countries makeing the
material much cheaper.

 

[RheillyPhoull]

On 2/07/2020 10:41 pm, Ralph Mowery wrote:

In article <rdjsa6$28b$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

Have you run this test with AC? That seems to be where the wheels come
off. I brought up this thread to a friend and he mentioned his quest to
repair some sort of HP true RMS meter that uses a thermocouple and heater
to properly measure complex waveforms. I can\'t even guess how slow such a
meter might be.

I had 3 or 4 of the Harbor Freight \'free\' multimeters. The ones that
usually sell for around $ 5. They seem to be reasonable accurate for
the money. Plenty accurate for the home user to test things around the
house. I do admit that the safety issue of putting them across the 120
or 240 volt power wires is somewhat doubtful. I sure would not use one
where I worked to put across the 480 volt 3 phase system that is fused
with 200 amps.

I\'m pretty timid with anything upstream from a plain outlet. I had an
edison base fuse burst in my hand once. Never seen one come apart before.
It was just a 120v lighting circuit, but right off the service panel.
There\'s way more excitement near those things.



I have not ran any tests for AC . The things I work with don\'t care
about very much about being accurate to more than around 5 %. Usually
it is more of do I have a voltage/current or not.

When I work on most anything other than low voltage (below 100 volts) I
ues either my Simpson 260 analog meter or a Fluke meter that is rated
for cat 3 and 4. If you have not heard of the Cat numbers, they are for
devices used in different power circuits. I don\'t know the numbers off
hand, but it goes something like this, Cat 1 is for low voltage items,
Cat 2 for things like stoves and refrigerators, Cat 3 for homw
wiring,and Cat 4 for the very high power circuits like I often worked on
like the 480 volt AC and 300 amps.

For a real scare you should see some of the safety movies that Fluke put
out. They show under test conditions what can hapen to inexpensive
meters and their meters under different conditions like having the
meter set for amps and putting across a 480 volt circuit that has plenty
of amps .

Ahh the old \"Leaving it on amps\" trick. How many of us can say they
never did it ?

 

[Jasen Betts]

On 2020-07-02, Ralph Mowery <rmowery28146@earthlink.net> wrote:

In article <rdjsa6$28b$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

Have you run this test with AC? That seems to be where the wheels come
off. I brought up this thread to a friend and he mentioned his quest to
repair some sort of HP true RMS meter that uses a thermocouple and heater
to properly measure complex waveforms. I can\'t even guess how slow such a
meter might be.

I had 3 or 4 of the Harbor Freight \'free\' multimeters. The ones that
usually sell for around $ 5. They seem to be reasonable accurate for
the money. Plenty accurate for the home user to test things around the
house. I do admit that the safety issue of putting them across the 120
or 240 volt power wires is somewhat doubtful. I sure would not use one
where I worked to put across the 480 volt 3 phase system that is fused
with 200 amps.

I\'m pretty timid with anything upstream from a plain outlet. I had an
edison base fuse burst in my hand once. Never seen one come apart before.
It was just a 120v lighting circuit, but right off the service panel.
There\'s way more excitement near those things.


I have not ran any tests for AC . The things I work with don\'t care
about very much about being accurate to more than around 5 %. Usually
it is more of do I have a voltage/current or not.

When I work on most anything other than low voltage (below 100 volts) I
ues either my Simpson 260 analog meter or a Fluke meter that is rated
for cat 3 and 4. If you have not heard of the Cat numbers, they are for
devices used in different power circuits. I don\'t know the numbers off
hand, but it goes something like this, Cat 1 is for low voltage items,
Cat 2 for things like stoves and refrigerators, Cat 3 for homw
wiring,and Cat 4 for the very high power circuits like I often worked on
like the 480 volt AC and 300 amps.

For a real scare you should see some of the safety movies that Fluke put
out. They show under test conditions what can hapen to inexpensive
meters and their meters under different conditions like having the
meter set for amps and putting across a 480 volt circuit that has plenty
of amps .

or even just this document.

https://content.fluke.com/promotions/promo-dmm/0518-dmm-campaign/dmm/fluke_dmm-chfr/files/safetyguidelines.pdf

--
Jasen.

 

[RheillyPhoull]

On 2/07/2020 10:41 pm, Ralph Mowery wrote:

In article <rdjsa6$28b$1@reader1.panix.com>, presence@MUNGEpanix.com
says...

Have you run this test with AC? That seems to be where the wheels come
off. I brought up this thread to a friend and he mentioned his quest to
repair some sort of HP true RMS meter that uses a thermocouple and heater
to properly measure complex waveforms. I can\'t even guess how slow such a
meter might be.

I had 3 or 4 of the Harbor Freight \'free\' multimeters. The ones that
usually sell for around $ 5. They seem to be reasonable accurate for
the money. Plenty accurate for the home user to test things around the
house. I do admit that the safety issue of putting them across the 120
or 240 volt power wires is somewhat doubtful. I sure would not use one
where I worked to put across the 480 volt 3 phase system that is fused
with 200 amps.

I\'m pretty timid with anything upstream from a plain outlet. I had an
edison base fuse burst in my hand once. Never seen one come apart before.
It was just a 120v lighting circuit, but right off the service panel.
There\'s way more excitement near those things.



I have not ran any tests for AC . The things I work with don\'t care
about very much about being accurate to more than around 5 %. Usually
it is more of do I have a voltage/current or not.

When I work on most anything other than low voltage (below 100 volts) I
ues either my Simpson 260 analog meter or a Fluke meter that is rated
for cat 3 and 4. If you have not heard of the Cat numbers, they are for
devices used in different power circuits. I don\'t know the numbers off
hand, but it goes something like this, Cat 1 is for low voltage items,
Cat 2 for things like stoves and refrigerators, Cat 3 for homw
wiring,and Cat 4 for the very high power circuits like I often worked on
like the 480 volt AC and 300 amps.

For a real scare you should see some of the safety movies that Fluke put
out. They show under test conditions what can hapen to inexpensive
meters and their meters under different conditions like having the
meter set for amps and putting across a 480 volt circuit that has plenty
of amps .

Ahh the old \"Leaving it on amps\" trick. How many of us can say they
never did it ?