Digital voltmeter inaccurate?

M

m

Guest
This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks nearly
new.

I find on several low ranges, the voltage reading is high by about 1.5%.
I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike
 
"ms" <msa@nospa.com> wrote in message news:3FC7A352.BFF08326@teleport.com...
This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks nearly
new.

I find on several low ranges, the voltage reading is high by about 1.5%.
I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike
Click to expand...
You didn't say what quantity that you're measuring that gives the high
reading. (AC? DC? Voltage? Current? Resistance?)
Assuming that you're measuring DC voltage, that reading is a bit high for a
quality meter such as an Amprobe. The higher quality meters usually have a
means of calibrating the various ranges, but you should get a service manual
that has the calibration procedure for the unit before you attempt to adjust
it. If absolute accuracy isn't critical, and you're sure that the other
meters are correct, then you can probably adjust the Amprobe unit to agree
with the others.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
 
The meter probably needs service or calibration. The first thing to
establish is if there are any defective parts. If not, then calibration is
necessary. To calibrate the meter yourself, you would need the service
manual, and the precision references to use for a standard. This also
depends on how accurate your requirements are.

If you call the manufacture, most have very reasonable rates to do a proper
servicing. If this is a low cost meter, it may not be worth it. We have a
number of meters in the service facility. These are sent out about once a
year for certification. The manufacture is charging very reasonable rates
for their work.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"ms" <msa@nospa.com> wrote in message news:3FC7A352.BFF08326@teleport.com...
This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks nearly
new.

I find on several low ranges, the voltage reading is high by about 1.5%.
I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike
 
Tweetldee wrote:
"ms" <msa@nospa.com> wrote in message news:3FC7A352.BFF08326@teleport.com...
This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks nearly
new.

I find on several low ranges, the voltage reading is high by about 1.5%.
I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike

You didn't say what quantity that you're measuring that gives the high
reading. (AC? DC? Voltage? Current? Resistance?)
Assuming that you're measuring DC voltage, that reading is a bit high for a
quality meter such as an Amprobe. The higher quality meters usually have a
means of calibrating the various ranges, but you should get a service manual
that has the calibration procedure for the unit before you attempt to adjust
it. If absolute accuracy isn't critical, and you're sure that the other
meters are correct, then you can probably adjust the Amprobe unit to agree
with the others.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
Click to expand...
I was measuring 13 VDC on 20 VDC range. Last week, I was on the 2 volt
range, and it measured several 1.5 VDC batteries high, and then a 9 VDC
battery high. Since several ranges are high by the same percentage, it
suggests to me not damage, but as built.

IMO this is a very low cost DVM, don't know the Amprobe brand, you say
it is quality?

The ranges are identical to my other $7.99 DVM's, making me think it has
a similar chip.

If any adjustment, would it be a pot on the circuit board? Or, how else?

Mike
 
ms wrote:
Tweetldee wrote:

"ms" <msa@nospa.com> wrote in message news:3FC7A352.BFF08326@teleport.com...
This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks nearly
new.

I find on several low ranges, the voltage reading is high by about 1.5%.
I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike

You didn't say what quantity that you're measuring that gives the high
reading. (AC? DC? Voltage? Current? Resistance?)
Assuming that you're measuring DC voltage, that reading is a bit high for a
quality meter such as an Amprobe. The higher quality meters usually have a
means of calibrating the various ranges, but you should get a service manual
that has the calibration procedure for the unit before you attempt to adjust
it. If absolute accuracy isn't critical, and you're sure that the other
meters are correct, then you can probably adjust the Amprobe unit to agree
with the others.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!

I was measuring 13 VDC on 20 VDC range. Last week, I was on the 2 volt
range, and it measured several 1.5 VDC batteries high, and then a 9 VDC
battery high. Since several ranges are high by the same percentage, it
suggests to me not damage, but as built.

IMO this is a very low cost DVM, don't know the Amprobe brand, you say
it is quality?

The ranges are identical to my other $7.99 DVM's, making me think it has
a similar chip.

If any adjustment, would it be a pot on the circuit board? Or, how else?

Mike
Click to expand...
BTW, this is an Amprobe AM-20, if this is familiar to you.

Mike
 
BTW, this may be totally obvious, but new Alkaline batteries measure somewhat
higher than their labeled voltage. Something like 1.58 V for a 1.5 V battery.

Maybe the other meters are reading low. :)

--- sam | Sci.Electronics.Repair FAQ Home Page: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Site Info: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: The email address in this message header may no longer work. To
contact me, please use the Feedback Form at repairfaq.org. Thanks.
 
If all ranges are reading out of tolearnce by the same amount, that's an
indication that the lowest basic voltage range setting is out of adjustment.
The lowest range adjustment sets the basic accuracy for most/all of the
higher ranges. I'm sure that wasn't the way it was built and sold.. it's
just out of adjustment. Equipment costing many thousands of dollars get out
of adjustment.. that's why they need calibration frequently.
You still need a service manual to determine which adjustment applies to the
basic voltage range. Don't just start arbitrarily twisting the adjustments
in the meter.. you'll mess things up for sure.
Amprobe instruments have been around for many years, and will probably be
around for many years to come. It's a well respected name in the meter
industry; not cheap by any means. After doing a couple minutes of surfing,
I see that the AM-20 is an economy model, with DC voltage spec'd at +/-1% of
reading +/-2 LSD. IOW, if your test battery terminal voltage is exactly 1.5
volts, the meter would be within specs with a reading between 1.483 and
1.517 volts. Your meter may just need a slight adjustment...
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
"ms" <msa@nospa.com> wrote in message news:3FC7E36A.EFCEE3B1@teleport.com...
Tweetldee wrote:

"ms" <msa@nospa.com> wrote in message
news:3FC7A352.BFF08326@teleport.com...
This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks
nearly
new.

I find on several low ranges, the voltage reading is high by about
1.5%.
I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike

You didn't say what quantity that you're measuring that gives the high
reading. (AC? DC? Voltage? Current? Resistance?)
Assuming that you're measuring DC voltage, that reading is a bit high
for a
quality meter such as an Amprobe. The higher quality meters usually
have a
means of calibrating the various ranges, but you should get a service
manual
that has the calibration procedure for the unit before you attempt to
adjust
it. If absolute accuracy isn't critical, and you're sure that the
other
meters are correct, then you can probably adjust the Amprobe unit to
agree
with the others.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in
the
address)

Never take a laxative and a sleeping pill at the same time!!

I was measuring 13 VDC on 20 VDC range. Last week, I was on the 2 volt
range, and it measured several 1.5 VDC batteries high, and then a 9 VDC
battery high. Since several ranges are high by the same percentage, it
suggests to me not damage, but as built.

IMO this is a very low cost DVM, don't know the Amprobe brand, you say
it is quality?

The ranges are identical to my other $7.99 DVM's, making me think it has
a similar chip.

If any adjustment, would it be a pot on the circuit board? Or, how else?

Mike
Click to expand...
 
ms wrote:
Tweetldee wrote:

"ms" <msa@nospa.com> wrote in message news:3FC7A352.BFF08326@teleport.com...

This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks nearly
new.

I find on several low ranges, the voltage reading is high by about 1.5%.
I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike

You didn't say what quantity that you're measuring that gives the high
reading. (AC? DC? Voltage? Current? Resistance?)
Assuming that you're measuring DC voltage, that reading is a bit high for a
quality meter such as an Amprobe. The higher quality meters usually have a
means of calibrating the various ranges, but you should get a service manual
that has the calibration procedure for the unit before you attempt to adjust
it. If absolute accuracy isn't critical, and you're sure that the other
meters are correct, then you can probably adjust the Amprobe unit to agree
with the others.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!


I was measuring 13 VDC on 20 VDC range. Last week, I was on the 2 volt
range, and it measured several 1.5 VDC batteries high, and then a 9 VDC
battery high. Since several ranges are high by the same percentage, it
suggests to me not damage, but as built.

IMO this is a very low cost DVM, don't know the Amprobe brand, you say
it is quality?

The ranges are identical to my other $7.99 DVM's, making me think it has
a similar chip.

If any adjustment, would it be a pot on the circuit board? Or, how else?

Mike
Click to expand...
Remember that the difference is the sum of the tolerances of the
instruments you're comparing.
If you decide to recalibrate it, the LAST thing you want to use as a
reference is a $7.99 DMM.
If you're measuring things where 1.5% is a problem, you need a MUCH
better meter than the $7.99 variety.
mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
Honda CB-125S
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
Sam Goldwasser wrote:
BTW, this may be totally obvious, but new Alkaline batteries measure somewhat
higher than their labeled voltage. Something like 1.58 V for a 1.5 V battery.
Click to expand...
Right. I got 1.55V each for a bunch of brand-new Ray-O-Vac AA cells.

--
"...people can quarrel with whether we should have more troops in Afghanistan
or internationalize Iraq or whatever, but it is incontestable that on the
day I left office, there were unaccounted-for stocks of biological and
chemical weapons." -- Bill Clinton, July 21, 2003, on the Larry King Show
 
Tweetldee wrote:
If all ranges are reading out of tolearnce by the same amount, that's an
indication that the lowest basic voltage range setting is out of adjustment.
The lowest range adjustment sets the basic accuracy for most/all of the
higher ranges. I'm sure that wasn't the way it was built and sold.. it's
just out of adjustment. Equipment costing many thousands of dollars get out
of adjustment.. that's why they need calibration frequently.
You still need a service manual to determine which adjustment applies to the
basic voltage range. Don't just start arbitrarily twisting the adjustments
in the meter.. you'll mess things up for sure.
Amprobe instruments have been around for many years, and will probably be
around for many years to come. It's a well respected name in the meter
industry; not cheap by any means. After doing a couple minutes of surfing,
I see that the AM-20 is an economy model, with DC voltage spec'd at +/-1% of
reading +/-2 LSD. IOW, if your test battery terminal voltage is exactly 1.5
volts, the meter would be within specs with a reading between 1.483 and
1.517 volts. Your meter may just need a slight adjustment...
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
"ms" <msa@nospa.com> wrote in message news:3FC7E36A.EFCEE3B1@teleport.com...
Tweetldee wrote:

"ms" <msa@nospa.com> wrote in message
news:3FC7A352.BFF08326@teleport.com...
This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks
nearly
new.

I find on several low ranges, the voltage reading is high by about
1.5%.
I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike

You didn't say what quantity that you're measuring that gives the high
reading. (AC? DC? Voltage? Current? Resistance?)
Assuming that you're measuring DC voltage, that reading is a bit high
for a
quality meter such as an Amprobe. The higher quality meters usually
have a
means of calibrating the various ranges, but you should get a service
manual
that has the calibration procedure for the unit before you attempt to
adjust
it. If absolute accuracy isn't critical, and you're sure that the
other
meters are correct, then you can probably adjust the Amprobe unit to
agree
with the others.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in
the
address)

Never take a laxative and a sleeping pill at the same time!!

I was measuring 13 VDC on 20 VDC range. Last week, I was on the 2 volt
range, and it measured several 1.5 VDC batteries high, and then a 9 VDC
battery high. Since several ranges are high by the same percentage, it
suggests to me not damage, but as built.

IMO this is a very low cost DVM, don't know the Amprobe brand, you say
it is quality?

The ranges are identical to my other $7.99 DVM's, making me think it has
a similar chip.

If any adjustment, would it be a pot on the circuit board? Or, how else?

Mike
Click to expand...
I opened it up, and no adjustments. Also, it looks identical to 4 other
inexpensive DVM's I have. They are 3 different brands, in the $5 to $20
range.

As Sam says, new alkaline cells read around 1.56 VDC. Only once, I found
a new one reading 1.61 !!.

I'm at home, no access to lab equipment for truly accurate measurements.
I think the other 3 DVM's are accurate for home use as they all read
very close, and the reading are what I **expect**. A new 1.5 V cell
reads 1.54... a used cell reads 1.4 or less, etc. These other DVM's read
that.

The Amprobe reads consistantly higher. As pointed out, it reads at the
top of it's tolerance, OK for someone, but gives me questionable data.

Some of you folk have much more experience than I do about this, but to
me this is simply an "as built" issue, not damage, and not repairable.

Maybe in assembly, one resistive element in that lot of circuit boards
was slightly wrong in value, so a bunch of circuit boards read at the
high edge of tolerance.

Again, if someone only has this one DVM, they would never know the
issue.

BTW, 2 of the units I have are from Harbor Freight, $5 imports that have
been working fine for the past 2 years.

Mike
 
ms wrote:
Tweetldee wrote:

If all ranges are reading out of tolearnce by the same amount, that's an
indication that the lowest basic voltage range setting is out of adjustment.
The lowest range adjustment sets the basic accuracy for most/all of the
higher ranges. I'm sure that wasn't the way it was built and sold.. it's
just out of adjustment. Equipment costing many thousands of dollars get out
of adjustment.. that's why they need calibration frequently.
You still need a service manual to determine which adjustment applies to the
basic voltage range. Don't just start arbitrarily twisting the adjustments
in the meter.. you'll mess things up for sure.
Amprobe instruments have been around for many years, and will probably be
around for many years to come. It's a well respected name in the meter
industry; not cheap by any means. After doing a couple minutes of surfing,
I see that the AM-20 is an economy model, with DC voltage spec'd at +/-1% of
reading +/-2 LSD. IOW, if your test battery terminal voltage is exactly 1.5
volts, the meter would be within specs with a reading between 1.483 and
1.517 volts. Your meter may just need a slight adjustment...
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
"ms" <msa@nospa.com> wrote in message news:3FC7E36A.EFCEE3B1@teleport.com...

Tweetldee wrote:

"ms" <msa@nospa.com> wrote in message

news:3FC7A352.BFF08326@teleport.com...

This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks

nearly

new.

I find on several low ranges, the voltage reading is high by about

1.5%.

I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike

You didn't say what quantity that you're measuring that gives the high
reading. (AC? DC? Voltage? Current? Resistance?)
Assuming that you're measuring DC voltage, that reading is a bit high

for a

quality meter such as an Amprobe. The higher quality meters usually

have a

means of calibrating the various ranges, but you should get a service

manual

that has the calibration procedure for the unit before you attempt to

adjust

it. If absolute accuracy isn't critical, and you're sure that the

other

meters are correct, then you can probably adjust the Amprobe unit to

agree

with the others.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in

the

address)

Never take a laxative and a sleeping pill at the same time!!

I was measuring 13 VDC on 20 VDC range. Last week, I was on the 2 volt
range, and it measured several 1.5 VDC batteries high, and then a 9 VDC
battery high. Since several ranges are high by the same percentage, it
suggests to me not damage, but as built.

IMO this is a very low cost DVM, don't know the Amprobe brand, you say
it is quality?

The ranges are identical to my other $7.99 DVM's, making me think it has
a similar chip.

If any adjustment, would it be a pot on the circuit board? Or, how else?

Mike


I opened it up, and no adjustments. Also, it looks identical to 4 other
inexpensive DVM's I have. They are 3 different brands, in the $5 to $20
range.

As Sam says, new alkaline cells read around 1.56 VDC. Only once, I found
a new one reading 1.61 !!.

I'm at home, no access to lab equipment for truly accurate measurements.
I think the other 3 DVM's are accurate for home use as they all read
very close, and the reading are what I **expect**. A new 1.5 V cell
reads 1.54... a used cell reads 1.4 or less, etc. These other DVM's read
that.

The Amprobe reads consistantly higher. As pointed out, it reads at the
top of it's tolerance, OK for someone, but gives me questionable data.

Some of you folk have much more experience than I do about this, but to
me this is simply an "as built" issue, not damage, and not repairable.

Maybe in assembly, one resistive element in that lot of circuit boards
was slightly wrong in value, so a bunch of circuit boards read at the
high edge of tolerance.

Again, if someone only has this one DVM, they would never know the
issue.

BTW, 2 of the units I have are from Harbor Freight, $5 imports that have
been working fine for the past 2 years.

Mike
Click to expand...
To quote an old saying:
A man with one watch always knows what time it is.
A man with two watches is never quite sure.
You have too many watches.
mike

--
Bunch of stuff For Sale and Wanted at the link below.
laptops and parts Test Equipment
Honda CB-125S
TEK Sampling Sweep Plugin and RM564
Tek 2465 $800, ham radio, 30pS pulser
Tektronix Concept Books, spot welding head...
http://www.geocities.com/SiliconValley/Monitor/4710/
 
"ms" bravely wrote to "All" (30 Nov 03 13:34:17)
--- on the heady topic of "Re: Digital voltmeter inaccurate?"

You might try a modern bandgap voltage reference IC. These can be bought
with varied precision ratings (price). For example the commonly found
(i.e. cheap) TL431 series has a basic +/-1% tolerance. There are even
more precise voltage references than this if you care to look them up.


ms> From: ms<msa@nospa.com>

ms> I opened it up, and no adjustments. Also, it looks identical to 4
ms> other inexpensive DVM's I have. They are 3 different brands, in the $5
ms> to $20 range.

ms> As Sam says, new alkaline cells read around 1.56 VDC. Only once, I
ms> found a new one reading 1.61 !!.

ms> I'm at home, no access to lab equipment for truly accurate
ms> measurements. I think the other 3 DVM's are accurate for home use as
ms> they all read very close, and the reading are what I **expect**. A new
ms> 1.5 V cell reads 1.54... a used cell reads 1.4 or less, etc. These
ms> other DVM's read that.

ms> The Amprobe reads consistantly higher. As pointed out, it reads at the
ms> top of it's tolerance, OK for someone, but gives me questionable data.

ms> Some of you folk have much more experience than I do about this, but
ms> to me this is simply an "as built" issue, not damage, and not
ms> repairable.
ms> Maybe in assembly, one resistive element in that lot of circuit
ms> boards was slightly wrong in value, so a bunch of circuit boards read
ms> at the high edge of tolerance.

ms> Again, if someone only has this one DVM, they would never know the
ms> issue.

ms> BTW, 2 of the units I have are from Harbor Freight, $5 imports that
ms> have been working fine for the past 2 years.

ms> Mike

.... Real techs don't lick nine-volt batteries!
 
ms wrote:
Tweetldee wrote:

If all ranges are reading out of tolearnce by the same amount, that's an
indication that the lowest basic voltage range setting is out of adjustment.
The lowest range adjustment sets the basic accuracy for most/all of the
higher ranges. I'm sure that wasn't the way it was built and sold.. it's
just out of adjustment. Equipment costing many thousands of dollars get out
of adjustment.. that's why they need calibration frequently.
You still need a service manual to determine which adjustment applies to the
basic voltage range. Don't just start arbitrarily twisting the adjustments
in the meter.. you'll mess things up for sure.
Amprobe instruments have been around for many years, and will probably be
around for many years to come. It's a well respected name in the meter
industry; not cheap by any means. After doing a couple minutes of surfing,
I see that the AM-20 is an economy model, with DC voltage spec'd at +/-1% of
reading +/-2 LSD. IOW, if your test battery terminal voltage is exactly 1.5
volts, the meter would be within specs with a reading between 1.483 and
1.517 volts. Your meter may just need a slight adjustment...
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)

Never take a laxative and a sleeping pill at the same time!!
"ms" <msa@nospa.com> wrote in message news:3FC7E36A.EFCEE3B1@teleport.com...
Tweetldee wrote:

"ms" <msa@nospa.com> wrote in message
news:3FC7A352.BFF08326@teleport.com...
This is an Amprobe DVM. I have 3 other DVM, other brands, and they all
read the same to the second digit.

I got this Amprobe at a garage sale, does not look abused, looks
nearly
new.

I find on several low ranges, the voltage reading is high by about
1.5%.
I know this is small in an analog VOM, but I'm used to digital meters
being accurate.

Could this be a high reading as built? That the chip used in the
voltmeter converts analog to digital in error? I realize if you bought
it new, and had no other comparison, you'd never know it was off.

Advice?

Mike

You didn't say what quantity that you're measuring that gives the high
reading. (AC? DC? Voltage? Current? Resistance?)
Assuming that you're measuring DC voltage, that reading is a bit high
for a
quality meter such as an Amprobe. The higher quality meters usually
have a
means of calibrating the various ranges, but you should get a service
manual
that has the calibration procedure for the unit before you attempt to
adjust
it. If absolute accuracy isn't critical, and you're sure that the
other
meters are correct, then you can probably adjust the Amprobe unit to
agree
with the others.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in
the
address)

Never take a laxative and a sleeping pill at the same time!!

I was measuring 13 VDC on 20 VDC range. Last week, I was on the 2 volt
range, and it measured several 1.5 VDC batteries high, and then a 9 VDC
battery high. Since several ranges are high by the same percentage, it
suggests to me not damage, but as built.

IMO this is a very low cost DVM, don't know the Amprobe brand, you say
it is quality?

The ranges are identical to my other $7.99 DVM's, making me think it has
a similar chip.

If any adjustment, would it be a pot on the circuit board? Or, how else?

Mike

I opened it up, and no adjustments. Also, it looks identical to 4 other
inexpensive DVM's I have. They are 3 different brands, in the $5 to $20
range.

As Sam says, new alkaline cells read around 1.56 VDC. Only once, I found
a new one reading 1.61 !!.

I'm at home, no access to lab equipment for truly accurate measurements.
I think the other 3 DVM's are accurate for home use as they all read
very close, and the reading are what I **expect**. A new 1.5 V cell
reads 1.54... a used cell reads 1.4 or less, etc. These other DVM's read
that.

The Amprobe reads consistantly higher. As pointed out, it reads at the
top of it's tolerance, OK for someone, but gives me questionable data.

Some of you folk have much more experience than I do about this, but to
me this is simply an "as built" issue, not damage, and not repairable.

Maybe in assembly, one resistive element in that lot of circuit boards
was slightly wrong in value, so a bunch of circuit boards read at the
high edge of tolerance.

Again, if someone only has this one DVM, they would never know the
issue.

BTW, 2 of the units I have are from Harbor Freight, $5 imports that have
been working fine for the past 2 years.

Mike
Click to expand...
One thing I should have mentioned in my OP, I'm not new to test
equipment, but on a budget in retirement so use cheap DVM's which, at
home, suffice.

Mike
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top