Test instrument accuracy vs stage testing during kit builds


James Compton
 

I may be over-thinking a problem I'm observing regarding some of my test equipment (specifically voltmeters) which I use during construction of kits and home-brew projects.  I just completed the SS-40HT and started the SS-40TX yesterday.  I had a few bogus step test readings when I was building the HT and now am "stuck" at the Step 4 Test in the TX.


I sent an email to Jim, but in the Step 4 test, I'm not getting a voltage drop.  The Step 2 & Step 3 test were satisfactory.....I think.....


Here's the rub.  I have several DVMs, including:  

Data Precision 1450 bench DVM

Wavetek BDM 35 bench DVM

2 Fluke 77 hand-held DVMs

Ideal 61-361 hand-held DVM

a couple of Simpson analog meters which belonged to my father.


My first problem was with the SS-40TX Step 3 Test where a voltage reading is supposed to be 0.2V or less than the power supply voltage.  Initially, it looked like the test was a success....until I started checking the output voltage of the "regulated" variable bench DC power supply.

Most of my voltmeters indicate that the actual output voltage is between .2 - .4 volts higher that the LED readout on the power supply itself.  (Example, when the bench supply shows 12.0 volts, the voltage at the tip of the cable measures 12.1 +/-

When I used a measured PCB input voltage instead of the bench supply voltage readout and conducted the Step 3 Test, I got 0.25 V difference.....which is above the recommended voltage difference.  Now.... was the test a PASS or FAIL?   Or is the 0.05 v excess voltage critical? And if the test FAILED, what am I supposed to do about it, assuming the build is correct at that point?


In the Step 4 TEST, I'm getting a 0.01 volt drop....supposed to be 0.2 volts.  Double and triple checked all components, solder joints, everything.....Test FAIL...  Now I'm stuck until I hear from Jim.  Looks like a problem with Q2....maybe?


Then, just because things were getting muddy, I compared the voltage readings of all 5 voltmeters using various DC power sources (batteries, bench supply, etc.).  The comparitive readings are inconsistent, but the best I'm seeing is an average of 0.03 volts difference of 4 and as much as 0.45 volts difference, usually from the Data Precision 1450.....BUT, it's not consistently the "black sheep" in the out-of-the average readings.


I'm getting paranoid.  I don't know how to test a "known" voltage source to determine which, if any, of these DVMs are accurate at any given reading, since I have no way of  knowing exactly what the voltage of any voltage source is, precisely.  And I don't know the degree of precision required when performing tests at various stages of building a kit.. 


It's very frustrating having so much money tied up in test equipment and having such inconsistent readings from multiple supposedly "precision" instruments.  And I just don't have the knowledge to calibrate the equipment or financial resources to have all the various pieces of test gear professionally calibrated.


Any comments, words of wisdom or advice?


Thanks.  Sorry for the long post!


Jim Compton, K4JDC


WA0ITP
 

GE Jim,

It's easy to get caught up searching for in the "exact" number, digital displays do that to us for sure.  Your Fluke should be plenty accurate enough for the job.  I always clip the DMM's gnd lead to the circuits ground, and make voltage readings on the board, not relying on the power supplies setting or display. If your ps is adjustable, set it at 12 volts at the input to the board.   What is the voltage on the collector of Q2?  Mine is 7.90 - remember that JP2 must be shorted to turn on Q2. If you have a reading near that, continue on, all is well.

btw I loved those old Simpson 260's.  I


On 6/21/2014 4:46 PM, jdcompton@... [4sqrp] wrote:

I may be over-thinking a problem I'm observing regarding some of my test equipment (specifically voltmeters) which I use during construction of kits and home-brew projects.  I just completed the SS-40HT and started the SS-40TX yesterday.  I had a few bogus step test readings when I was building the HT and now am "stuck" at the Step 4 Test in the TX.


I sent an email to Jim, but in the Step 4 test, I'm not getting a voltage drop.  The Step 2 & Step 3 test were satisfactory.....I think.....


Here's the rub.  I have several DVMs, including:  

Data Precision 1450 bench DVM

Wavetek BDM 35 bench DVM

2 Fluke 77 hand-held DVMs

Ideal 61-361 hand-held DVM

a couple of Simpson analog meters which belonged to my father.


My first problem was with the SS-40TX Step 3 Test where a voltage reading is supposed to be 0.2V or less than the power supply voltage.  Initially, it looked like the test was a success....until I started checking the output voltage of the "regulated" variable bench DC power supply.

Most of my voltmeters indicate that the actual output voltage is between .2 - .4 volts higher that the LED readout on the power supply itself.  (Example, when the bench supply shows 12.0 volts, the voltage at the tip of the cable measures 12.1 +/-

When I used a measured PCB input voltage instead of the bench supply voltage readout and conducted the Step 3 Test, I got 0.25 V difference.....which is above the recommended voltage difference.  Now.... was the test a PASS or FAIL?   Or is the 0.05 v excess voltage critical? And if the test FAILED, what am I supposed to do about it, assuming the build is correct at that point?


In the Step 4 TEST, I'm getting a 0.01 volt drop....supposed to be 0.2 volts.  Double and triple checked all components, solder joints, everything.....Test FAIL...  Now I'm stuck until I hear from Jim.  Looks like a problem with Q2....maybe?


Then, just because things were getting muddy, I compared the voltage readings of all 5 voltmeters using various DC power sources (batteries, bench supply, etc.).  The comparitive readings are inconsistent, but the best I'm seeing is an average of 0.03 volts difference of 4 and as much as 0.45 volts difference, usually from the Data Precision 1450.....BUT, it's not consistently the "black sheep" in the out-of-the average readings.


I'm getting paranoid.  I don't know how to test a "known" voltage source to determine which, if any, of these DVMs are accurate at any given reading, since I have no way of  knowing exactly what the voltage of any voltage source is, precisely.  And I don't know the degree of precision required when performing tests at various stages of building a kit.. 


It's very frustrating having so much money tied up in test equipment and having such inconsistent readings from multiple supposedly "precision" instruments.  And I just don't have the knowledge to calibrate the equipment or financial resources to have all the various pieces of test gear professionally calibrated.


Any comments, words of wisdom or advice?


Thanks.  Sorry for the long post!


Jim Compton, K4JDC


-- 
72 WAØITP
I love this radio stuff.
www.wa0itp.com
www.4sqrp.com


Don Wilhelm <w3fpr@...>
 

Jim,

Precision and accuracy are two different things.
If a voltmeter is capable on showing 4 digits, that is an indication of the precision - in other words, the steps from one displayed value to the adjacent value.
Accuracy is a measure of just how true to a voltage standard any of those readings may be.

So you have lots of precision, but there is a question about accuracy of your various instruments.
You are like the man with many watches but does not know what time it is.

I do have a Precision Voltage Reference on my website that you can build and use to determine the accuracy of your various voltmeters.  Go to www.w3fpr.com and click on the article in the left column.

73,
Don W3FPR

On 6/21/2014 5:46 PM, jdcompton@... [4sqrp] wrote:
 

I may be over-thinking a problem I'm observing regarding some of my test equipment (specifically voltmeters) which I use during construction of kits and home-brew projects.  I just completed the SS-40HT and started the SS-40TX yesterday.  I had a few bogus step test readings when I was building the HT and now am "stuck" at the Step 4 Test in the TX.


I sent an email to Jim, but in the Step 4 test, I'm not getting a voltage drop.  The Step 2 & Step 3 test were satisfactory.....I think.....


Here's the rub.  I have several DVMs, including:  

Data Precision 1450 bench DVM

Wavetek BDM 35 bench DVM

2 Fluke 77 hand-held DVMs

Ideal 61-361 hand-held DVM

a couple of Simpson analog meters which belonged to my father.


My first problem was with the SS-40TX Step 3 Test where a voltage reading is supposed to be 0.2V or less than the power supply voltage.  Initially, it looked like the test was a success....until I started checking the output voltage of the "regulated" variable bench DC power supply.

Most of my voltmeters indicate that the actual output voltage is between .2 - .4 volts higher that the LED readout on the power supply itself.  (Example, when the bench supply shows 12.0 volts, the voltage at the tip of the cable measures 12.1 +/-

When I used a measured PCB input voltage instead of the bench supply voltage readout and conducted the Step 3 Test, I got 0.25 V difference.....which is above the recommended voltage difference.  Now.... was the test a PASS or FAIL?   Or is the 0.05 v excess voltage critical? And if the test FAILED, what am I supposed to do about it, assuming the build is correct at that point?


In the Step 4 TEST, I'm getting a 0.01 volt drop....supposed to be 0.2 volts.  Double and triple checked all components, solder joints, everything.....Test FAIL...  Now I'm stuck until I hear from Jim.  Looks like a problem with Q2....maybe?


Then, just because things were getting muddy, I compared the voltage readings of all 5 voltmeters using various DC power sources (batteries, bench supply, etc.).  The comparitive readings are inconsistent, but the best I'm seeing is an average of 0.03 volts difference of 4 and as much as 0.45 volts difference, usually from the Data Precision 1450.....BUT, it's not consistently the "black sheep" in the out-of-the average readings.


I'm getting paranoid.  I don't know how to test a "known" voltage source to determine which, if any, of these DVMs are accurate at any given reading, since I have no way of  knowing exactly what the voltage of any voltage source is, precisely.  And I don't know the degree of precision required when performing tests at various stages of building a kit.. 


It's very frustrating having so much money tied up in test equipment and having such inconsistent readings from multiple supposedly "precision" instruments.  And I just don't have the knowledge to calibrate the equipment or financial resources to have all the various pieces of test gear professionally calibrated.


Any comments, words of wisdom or advice?


Thanks.  Sorry for the long post!


Jim Compton, K4JDC




James Compton
 

Thanks for the reply!  I'll check the Q2  collector voltage in the morning.  Thanks for the tip!
Jim C.

-----Original Message-----
From: "WA0ITP wa0itp@... [4sqrp]" <4sqrp@...>
Sent: Jun 21, 2014 6:43 PM
To: 4sqrp@..., jdcompton@...
Subject: Re: [4sqrp] Test instrument accuracy vs stage testing during kit builds

GE Jim,

It's easy to get caught up searching for in the "exact" number, digital
displays do that to us for sure. Your Fluke should be plenty accurate
enough for the job. I always clip the DMM's gnd lead to the circuits
ground, and make voltage readings on the board, not relying on the power
supplies setting or display. If your ps is adjustable, set it at 12
volts at the input to the board. What is the voltage on the collector
of Q2? Mine is 7.90 - remember that JP2 must be shorted to turn on Q2.
If you have a reading near that, continue on, all is well.

btw I loved those old Simpson 260's. I


On 6/21/2014 4:46 PM, jdcompton@... [4sqrp] wrote:
>
>
> I may be over-thinking a problem I'm observing regarding some of my
> test equipment (specifically voltmeters) which I use during
> construction of kits and home-brew projects. I just completed the
> SS-40HT and started the SS-40TX yesterday. I had a few bogus step
> test readings when I was building the HT and now am "stuck" at the
> Step 4 Test in the TX.
>
>
> I sent an email to Jim, but in the Step 4 test, I'm not getting a
> voltage drop. The Step 2 & Step 3 test were satisfactory.....I think.....
>
>
> Here's the rub. I have several DVMs, including:
>
> Data Precision 1450 bench DVM
>
> Wavetek BDM 35 bench DVM
>
> 2 Fluke 77 hand-held DVMs
>
> Ideal 61-361 hand-held DVM
>
> a couple of Simpson analog meters which belonged to my father.
>
>
> My first problem was with the SS-40TX Step 3 Test where a voltage
> reading is supposed to be 0.2V or less than the power supply voltage.
> Initially, it looked like the test was a success....until I started
> checking the output voltage of the "regulated" variable bench DC power
> supply.
>
> Most of my voltmeters indicate that the actual output voltage is
> between .2 - .4 volts higher that the LED readout on the power supply
> itself. (Example, when the bench supply shows 12.0 volts, the voltage
> at the tip of the cable measures 12.1 +/-
>
> When I used a measured PCB input voltage instead of the bench supply
> voltage readout and conducted the Step 3 Test, I got 0.25 V
> difference.....which is above the recommended voltage difference.
> Now.... was the test a PASS or FAIL? Or is the 0.05 v excess
> voltage critical? And if the test FAILED, what am I supposed to do
> about it, assuming the build is correct at that point?
>
>
> In the Step 4 TEST, I'm getting a 0.01 volt drop....supposed to be 0.2
> volts. Double and triple checked all components, solder joints,
> everything.....Test FAIL... Now I'm stuck until I hear from Jim.
> Looks like a problem with Q2....maybe?
>
>
> Then, just because things were getting muddy, I compared the voltage
> readings of all 5 voltmeters using various DC power sources
> (batteries, bench supply, etc.). The comparitive readings are
> inconsistent, but the best I'm seeing is an average of 0.03 volts
> difference of 4 and as much as 0.45 volts difference, usually from the
> Data Precision 1450.....BUT, it's not consistently the "black sheep"
> in the out-of-the average readings.
>
>
> I'm getting paranoid. I don't know how to test a "known" voltage
> source to determine which, if any, of these DVMs are accurate at any
> given reading, since I have no way of knowing exactly what the
> voltage of any voltage source is, precisely. And I don't know the
> degree of precision required when performing tests at various stages
> of building a kit..
>
>
> It's very frustrating having so much money tied up in test equipment
> and having such inconsistent readings from multiple supposedly
> "precision" instruments. And I just don't have the knowledge to
> calibrate the equipment or financial resources to have all the various
> pieces of test gear professionally calibrated.
>
>
> Any comments, words of wisdom or advice?
>
>
> Thanks. Sorry for the long post!
>
>
> Jim Compton, K4JDC
>
>
>
>

--
72 WAØITP
I love this radio stuff.
www.wa0itp.com
www.4sqrp.com


James Compton
 

Don,
Just what I am looking for!  You're analogy about the man with many watches couldn't be more appropriate!
One additional question, after building the Precision Voltage Reference, do you try to actually calibrate your specific voltmeter or do you just apply the difference between the accurate voltage and your voltmeter reading to subsequent voltmeter readings?  I ask because I don't think I would know how to calibrate my several voltmeters unless I could find a procedure in a manual.....if I could find manuals online.
Thanks, again!
Jim Compton, K4JDC
-----Original Message-----
From: "Don Wilhelm w3fpr@... [4sqrp]" <4sqrp@...>
Sent: Jun 21, 2014 6:46 PM
To: 4sqrp@..., jdcompton@...
Subject: Re: [4sqrp] Test instrument accuracy vs stage testing during kit builds

Jim,

Precision and accuracy are two different things.
If a voltmeter is capable on showing 4 digits, that is an indication of
the precision - in other words, the steps from one displayed value to
the adjacent value.
Accuracy is a measure of just how true to a voltage standard any of
those readings may be.

So you have lots of precision, but there is a question about accuracy of
your various instruments.
You are like the man with many watches but does not know what time it is.

I do have a Precision Voltage Reference on my website that you can build
and use to determine the accuracy of your various voltmeters. Go to
www.w3fpr.com and click on the article in the left column.

73,
Don W3FPR

On 6/21/2014 5:46 PM, jdcompton@... [4sqrp] wrote:
>
> I may be over-thinking a problem I'm observing regarding some of my
> test equipment (specifically voltmeters) which I use during
> construction of kits and home-brew projects. I just completed the
> SS-40HT and started the SS-40TX yesterday. I had a few bogus step
> test readings when I was building the HT and now am "stuck" at the
> Step 4 Test in the TX.
>
>
> I sent an email to Jim, but in the Step 4 test, I'm not getting a
> voltage drop. The Step 2 & Step 3 test were satisfactory.....I think.....
>
>
> Here's the rub. I have several DVMs, including:
>
> Data Precision 1450 bench DVM
>
> Wavetek BDM 35 bench DVM
>
> 2 Fluke 77 hand-held DVMs
>
> Ideal 61-361 hand-held DVM
>
> a couple of Simpson analog meters which belonged to my father.
>
>
> My first problem was with the SS-40TX Step 3 Test where a voltage
> reading is supposed to be 0.2V or less than the power supply voltage.
> Initially, it looked like the test was a success....until I started
> checking the output voltage of the "regulated" variable bench DC power
> supply.
>
> Most of my voltmeters indicate that the actual output voltage is
> between .2 - .4 volts higher that the LED readout on the power supply
> itself. (Example, when the bench supply shows 12.0 volts, the voltage
> at the tip of the cable measures 12.1 +/-
>
> When I used a measured PCB input voltage instead of the bench supply
> voltage readout and conducted the Step 3 Test, I got 0.25 V
> difference.....which is above the recommended voltage difference.
> Now.... was the test a PASS or FAIL? Or is the 0.05 v excess
> voltage critical? And if the test FAILED, what am I supposed to do
> about it, assuming the build is correct at that point?
>
>
> In the Step 4 TEST, I'm getting a 0.01 volt drop....supposed to be 0.2
> volts. Double and triple checked all components, solder joints,
> everything.....Test FAIL... Now I'm stuck until I hear from Jim.
> Looks like a problem with Q2....maybe?
>
>
> Then, just because things were getting muddy, I compared the voltage
> readings of all 5 voltmeters using various DC power sources
> (batteries, bench supply, etc.). The comparitive readings are
> inconsistent, but the best I'm seeing is an average of 0.03 volts
> difference of 4 and as much as 0.45 volts difference, usually from the
> Data Precision 1450.....BUT, it's not consistently the "black sheep"
> in the out-of-the average readings.
>
>
> I'm getting paranoid. I don't know how to test a "known" voltage
> source to determine which, if any, of these DVMs are accurate at any
> given reading, since I have no way of knowing exactly what the
> voltage of any voltage source is, precisely. And I don't know the
> degree of precision required when performing tests at various stages
> of building a kit..
>
>
> It's very frustrating having so much money tied up in test equipment
> and having such inconsistent readings from multiple supposedly
> "precision" instruments. And I just don't have the knowledge to
> calibrate the equipment or financial resources to have all the various
> pieces of test gear professionally calibrated.
>
>
> Any comments, words of wisdom or advice?
>
>
> Thanks. Sorry for the long post!
>
>
> Jim Compton, K4JDC
>
>


Don Wilhelm <w3fpr@...>
 

Jim,

If the instrument has an adjustment, by all means adjust it.
If there is no adjustment, then a "sticky" on the meter to show the amount of deviation may be the best solution.

As for precision, normally 2 significant digits is all that is appropriate.  In other words, a voltage reading of 2.456 volts can be rounded to 2.5 volts and be entirely adequate for most measurements.
The nice part about having extra precision is that one may be able to measure small differences in voltage when one is tracing voltage drops due to unwanted resistance in the circuit.
As an example, a voltage of 13.256 at the power supply and a voltage of 13.225 at the rig end would indicate a drop of 0.031 volts - again notice that 2 significant digits is appropriate, but it took a measurement of 5 significant digits to determine the voltage drop.  How much precision is necessary depends on the measurement to be made.

Most measurements of such things as the voltage of transistor leads can be limited to 2 significant digits - remember that resistors and capacitors are usually of the 5% variety, so voltage differences that vary only in the 3rd significant digit are swamped out by the component tolerances.  Use the 3rd digit for the indicator of whether to increase or decrease the 2nd significant digit - remember "rounding off" from high school math - it is appropriate here.

73,
Don W3FPR

On 6/21/2014 7:30 PM, Jim Compton jdcompton@... [4sqrp] wrote:
 
Don,
Just what I am looking for!  You're analogy about the man with many watches couldn't be more appropriate!
One additional question, after building the Precision Voltage Reference, do you try to actually calibrate your specific voltmeter or do you just apply the difference between the accurate voltage and your voltmeter reading to subsequent voltmeter readings?  I ask because I don't think I would know how to calibrate my several voltmeters unless I could find a procedure in a manual.....if I could find manuals online.
Thanks, again!
Jim Compton, K4JDC
-----Original Message-----
From: "Don Wilhelm w3fpr@... [4sqrp]" <4sqrp@...>
Sent: Jun 21, 2014 6:46 PM
To: 4sqrp@..., jdcompton@...
Subject: Re: [4sqrp] Test instrument accuracy vs stage testing during kit builds

Jim,

Precision and accuracy are two different things.
If a voltmeter is capable on showing 4 digits, that is an indication of
the precision - in other words, the steps from one displayed value to
the adjacent value.
Accuracy is a measure of just how true to a voltage standard any of
those readings may be.

So you have lots of precision, but there is a question about accuracy of
your various instruments.
You are like the man with many watches but does not know what time it is.

I do have a Precision Voltage Reference on my website that you can build
and use to determine the accuracy of your various voltmeters. Go to
www.w3fpr.com and click on the article in the left column.

73,
Don W3FPR

On 6/21/2014 5:46 PM, jdcompton@... [4sqrp] wrote:
>
> I may be over-thinking a problem I'm observing regarding some of my
> test equipment (specifically voltmeters) which I use during
> construction of kits and home-brew projects. I just completed the
> SS-40HT and started the SS-40TX yesterday. I had a few bogus step
> test readings when I was building the HT and now am "stuck" at the
> Step 4 Test in the TX.
>
>
> I sent an email to Jim, but in the Step 4 test, I'm not getting a
> voltage drop. The Step 2 & Step 3 test were satisfactory.....I think.....
>
>
> Here's the rub. I have several DVMs, including:
>
> Data Precision 1450 bench DVM
>
> Wavetek BDM 35 bench DVM
>
> 2 Fluke 77 hand-held DVMs
>
> Ideal 61-361 hand-held DVM
>
> a couple of Simpson analog meters which belonged to my father.
>
>
> My first problem was with the SS-40TX Step 3 Test where a voltage
> reading is supposed to be 0.2V or less than the power supply voltage.
> Initially, it looked like the test was a success....until I started
> checking the output voltage of the "regulated" variable bench DC power
> supply.
>
> Most of my voltmeters indicate that the actual output voltage is
> between .2 - .4 volts higher that the LED readout on the power supply
> itself. (Example, when the bench supply shows 12.0 volts, the voltage
> at the tip of the cable measures 12.1 +/-
>
> When I used a measured PCB input voltage instead of the bench supply
> voltage readout and conducted the Step 3 Test, I got 0.25 V
> difference.....which is above the recommended voltage difference.
> Now.... was the test a PASS or FAIL? Or is the 0.05 v excess
> voltage critical? And if the test FAILED, what am I supposed to do
> about it, assuming the build is correct at that point?
>
>
> In the Step 4 TEST, I'm getting a 0.01 volt drop....supposed to be 0.2
> volts. Double and triple checked all components, solder joints,
> everything.....Test FAIL... Now I'm stuck until I hear from Jim.
> Looks like a problem with Q2....maybe?
>
>
> Then, just because things were getting muddy, I compared the voltage
> readings of all 5 voltmeters using various DC power sources
> (batteries, bench supply, etc.). The comparitive readings are
> inconsistent, but the best I'm seeing is an average of 0.03 volts
> difference of 4 and as much as 0.45 volts difference, usually from the
> Data Precision 1450.....BUT, it's not consistently the "black sheep"
> in the out-of-the average readings.
>
>
> I'm getting paranoid. I don't know how to test a "known" voltage
> source to determine which, if any, of these DVMs are accurate at any
> given reading, since I have no way of knowing exactly what the
> voltage of any voltage source is, precisely. And I don't know the
> degree of precision required when performing tests at various stages
> of building a kit..
>
>
> It's very frustrating having so much money tied up in test equipment
> and having such inconsistent readings from multiple supposedly
> "precision" instruments. And I just don't have the knowledge to
> calibrate the equipment or financial resources to have all the various
> pieces of test gear professionally calibrated.
>
>
> Any comments, words of wisdom or advice?
>
>
> Thanks. Sorry for the long post!
>
>
> Jim Compton, K4JDC
>
>



James Compton
 

Thanks, Don.  I appreciate the information.
Jim C,

-----Original Message-----
From: "Don Wilhelm w3fpr@... [4sqrp]" <4sqrp@...>
Sent: Jun 21, 2014 8:24 PM
To: 4sqrp@..., Jim Compton
Subject: Re: [4sqrp] Test instrument accuracy vs stage testing during kit builds

Jim,

If the instrument has an adjustment, by all means adjust it.
If there is no adjustment, then a "sticky" on the meter to show the
amount of deviation may be the best solution.

As for precision, normally 2 significant digits is all that is
appropriate. In other words, a voltage reading of 2.456 volts can be
rounded to 2.5 volts and be entirely adequate for most measurements.
The nice part about having extra precision is that one may be able to
measure small differences in voltage when one is tracing voltage drops
due to unwanted resistance in the circuit.
As an example, a voltage of 13.256 at the power supply and a voltage of
13.225 at the rig end would indicate a drop of 0.031 volts - again
notice that 2 significant digits is appropriate, but it took a
measurement of 5 significant digits to determine the voltage drop. How
much precision is necessary depends on the measurement to be made.

Most measurements of such things as the voltage of transistor leads can
be limited to 2 significant digits - remember that resistors and
capacitors are usually of the 5% variety, so voltage differences that
vary only in the 3rd significant digit are swamped out by the component
tolerances. Use the 3rd digit for the indicator of whether to increase
or decrease the 2nd significant digit - remember "rounding off" from
high school math - it is appropriate here.

73,
Don W3FPR

On 6/21/2014 7:30 PM, Jim Compton jdcompton@... [4sqrp] wrote:
>
> Don,
>
> Just what I am looking for! You're analogy about the man with
> many watches couldn't be more appropriate!
>
> One additional question, after building the Precision Voltage
> Reference, do you try to actually calibrate your specific
> voltmeter or do you just apply the difference between the accurate
> voltage and your voltmeter reading to subsequent voltmeter
> readings? I ask because I don't think I would know how to
> calibrate my several voltmeters unless I could find a procedure in
> a manual.....if I could find manuals online.
>
> Thanks, again!
>
> Jim Compton, K4JDC
>
> -----Original Message-----
> From: "Don Wilhelm w3fpr@... [4sqrp]"
> <4sqrp@...>
> Sent: Jun 21, 2014 6:46 PM
> To: 4sqrp@..., jdcompton@...
> Subject: Re: [4sqrp] Test instrument accuracy vs stage testing
> during kit builds
>
> Jim,
>
> Precision and accuracy are two different things.
> If a voltmeter is capable on showing 4 digits, that is an
> indication of
> the precision - in other words, the steps from one displayed value to
> the adjacent value.
> Accuracy is a measure of just how true to a voltage standard any of
> those readings may be.
>
> So you have lots of precision, but there is a question about
> accuracy of
> your various instruments.
> You are like the man with many watches but does not know what time
> it is.
>
> I do have a Precision Voltage Reference on my website that you can
> build
> and use to determine the accuracy of your various voltmeters. Go to
> www.w3fpr.com and click on the article in the left column.
>
> 73,
> Don W3FPR
>
> On 6/21/2014 5:46 PM, jdcompton@... [4sqrp] wrote:
> >
> > I may be over-thinking a problem I'm observing regarding some of my
> > test equipment (specifically voltmeters) which I use during
> > construction of kits and home-brew projects. I just completed the
> > SS-40HT and started the SS-40TX yesterday. I had a few bogus step
> > test readings when I was building the HT and now am "stuck" at the
> > Step 4 Test in the TX.
> >
> >
> > I sent an email to Jim, but in the Step 4 test, I'm not getting a
> > voltage drop. The Step 2 & Step 3 test were satisfactory.....I
> think.....
> >
> >
> > Here's the rub. I have several DVMs, including:
> >
> > Data Precision 1450 bench DVM
> >
> > Wavetek BDM 35 bench DVM
> >
> > 2 Fluke 77 hand-held DVMs
> >
> > Ideal 61-361 hand-held DVM
> >
> > a couple of Simpson analog meters which belonged to my father.
> >
> >
> > My first problem was with the SS-40TX Step 3 Test where a voltage
> > reading is supposed to be 0.2V or less than the power supply
> voltage.
> > Initially, it looked like the test was a success....until I started
> > checking the output voltage of the "regulated" variable bench DC
> power
> > supply.
> >
> > Most of my voltmeters indicate that the actual output voltage is
> > between .2 - .4 volts higher that the LED readout on the power
> supply
> > itself. (Example, when the bench supply shows 12.0 volts, the
> voltage
> > at the tip of the cable measures 12.1 +/-
> >
> > When I used a measured PCB input voltage instead of the bench
> supply
> > voltage readout and conducted the Step 3 Test, I got 0.25 V
> > difference.....which is above the recommended voltage difference.
> > Now.... was the test a PASS or FAIL? Or is the 0.05 v excess
> > voltage critical? And if the test FAILED, what am I supposed to do
> > about it, assuming the build is correct at that point?
> >
> >
> > In the Step 4 TEST, I'm getting a 0.01 volt drop....supposed to
> be 0.2
> > volts. Double and triple checked all components, solder joints,
> > everything.....Test FAIL... Now I'm stuck until I hear from Jim.
> > Looks like a problem with Q2....maybe?
> >
> >
> > Then, just because things were getting muddy, I compared the
> voltage
> > readings of all 5 voltmeters using various DC power sources
> > (batteries, bench supply, etc.). The comparitive readings are
> > inconsistent, but the best I'm seeing is an average of 0.03 volts
> > difference of 4 and as much as 0.45 volts difference, usually
> from the
> > Data Precision 1450.....BUT, it's not consistently the "black
> sheep"
> > in the out-of-the average readings.
> >
> >
> > I'm getting paranoid. I don't know how to test a "known" voltage
> > source to determine which, if any, of these DVMs are accurate at
> any
> > given reading, since I have no way of knowing exactly what the
> > voltage of any voltage source is, precisely. And I don't know the
> > degree of precision required when performing tests at various
> stages
> > of building a kit..
> >
> >
> > It's very frustrating having so much money tied up in test
> equipment
> > and having such inconsistent readings from multiple supposedly
> > "precision" instruments. And I just don't have the knowledge to
> > calibrate the equipment or financial resources to have all the
> various
> > pieces of test gear professionally calibrated.
> >
> >
> > Any comments, words of wisdom or advice?
> >
> >
> > Thanks. Sorry for the long post!
> >
> >
> > Jim Compton, K4JDC
> >
> >
>
>