Re: [time-nuts] 5 Digit Panel meters

[Bob kb8tq]

Hi

Update rate on the specific part mentioned earlier is five a second. Assuming 
that is correct, it would 
rule out them using the MCP3421 at 18 bits. It will not go that fast at that 
resolution. It also seems odd that
they would have a +/- capable part with built in ability to auto range, and not 
utilize those features.

Bob

> On Sep 7, 2020, at 8:24 PM, Robert LaJeunesse  wrote:
> 
> The similar meters I have are based on the Microchip MCP3421, a tiny 6-pin 
> SOT 18 bit ADC with internal 2.048V 15 ppm (typ) reference, differential 
> inputs, and a PGA. Input span is +/-2.048V at minimum gain to +/-0.256V with 
> a PGA gain of 8. So at max gain 1 LSB is about 2uV, although I'd be surprised 
> if it was that quiet (the spec at PGA=1 is 1.5uV typical, no max given). 
> Initial accuracy is not great at 0.35% max, but that can be trimmed out 
> externally or via software. For an 18 bit ADC with a decent reference it's 
> actually a rather good deal at under US $2 (qty 25+). Just don't expect it to 
> be an accurate 18 bits over a wide temp range, references like that don't 
> sell so cheap.
> 
> Bob L.
> 
> ref: https://ww1.microchip.com/downloads/en/DeviceDoc/22003e.pdf
> 
>> Sent: Monday, September 07, 2020 at 1:15 PM
>> From: "Bob kb8tq" 
>> To: "Discussion of precise time and frequency measurement" 
>> 
>> Subject: Re: [time-nuts] 5 Digit Panel meters
>> 
>> Hi
>> 
>> So, *assuming* there is no other ADC on the board ….
>> 
>> DC performance of the STM8 ADC’s is somewhere in the 8 to 9 bit range as far
>> as ENOB with significant averaging. For the sake of simplicity, let’s say 
>> they *do*
>> make it to 10 bits. 
>> 
>> But … do we get the 10 bits?
>> 
>> The range on the meter is 33V. The reference to the DAC is (likely) 5V. You 
>> just lost
>> nearly 3 bits from that scale mismatch.  At the 5V level, you would be 
>> running just over
>> 7 of your (ideal) 10 bits. 
>> 
>> Net result is that you are trying to check a 16 bit gizmo with a not quite 8 
>> bit device.
>> 
>> Bob
> 
> 
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Re: [time-nuts] 5 Digit Panel meters

[Robert LaJeunesse]

The similar meters I have are based on the Microchip MCP3421, a tiny 6-pin SOT 
18 bit ADC with internal 2.048V 15 ppm (typ) reference, differential inputs, 
and a PGA. Input span is +/-2.048V at minimum gain to +/-0.256V with a PGA gain 
of 8. So at max gain 1 LSB is about 2uV, although I'd be surprised if it was 
that quiet (the spec at PGA=1 is 1.5uV typical, no max given). Initial accuracy 
is not great at 0.35% max, but that can be trimmed out externally or via 
software. For an 18 bit ADC with a decent reference it's actually a rather good 
deal at under US $2 (qty 25+). Just don't expect it to be an accurate 18 bits 
over a wide temp range, references like that don't sell so cheap.

Bob L.

ref: https://ww1.microchip.com/downloads/en/DeviceDoc/22003e.pdf

> Sent: Monday, September 07, 2020 at 1:15 PM
> From: "Bob kb8tq" 
> To: "Discussion of precise time and frequency measurement" 
> 
> Subject: Re: [time-nuts] 5 Digit Panel meters
>
> Hi
> 
> So, *assuming* there is no other ADC on the board ….
> 
> DC performance of the STM8 ADC’s is somewhere in the 8 to 9 bit range as far
> as ENOB with significant averaging. For the sake of simplicity, let’s say 
> they *do*
> make it to 10 bits. 
> 
> But … do we get the 10 bits?
> 
> The range on the meter is 33V. The reference to the DAC is (likely) 5V. You 
> just lost
> nearly 3 bits from that scale mismatch.  At the 5V level, you would be 
> running just over
> 7 of your (ideal) 10 bits. 
> 
> Net result is that you are trying to check a 16 bit gizmo with a not quite 8 
> bit device.
> 
> Bob


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Re: [time-nuts] Impedance question

[Gary Chatters]

Someone else will have to give you the answers, but here are a couple of 
issues to consider:


How long will your cables be?

A wavelength at 10 MHz is 30 meters.  A quarter wave (7.5m) coax line 
sort of inverts the termination impedance.  So if you connect using a 
high impedance, your source will be almost a short circuit (milliohms). 
Nominally, I would assume that you are working on a bench with short 50 
ohm cables, so not much of a problem, but assuming can have unintended 
consequences.


What is the voltage level of your sources?

Your counters will have a limit as to how much power input they can 
tolerate.  P=E^2/R.  The voltage that the 50 ohm input can tolerate may 
be much lower that what the megohm impedance can tolerate.  My 5334A 
says 5V RMS max when load set to 50 ohms.  Again, don't assume, check.


Gary




On 9/7/20 8:03 PM, SimBeej wrote:

Dear fellow Time-Nuts,

I have a question about impedance matching (and I apologise in advance for
my blatant ignorance on this matter, but I don't have a background in
electronics and hardware, so am having to learn along the way).

When using frequency counters (in my case a 53230A and SR620) for making
frequency or time interval measurements, should I be choosing 50 ohm for 1
mega ohm as the input impedance (where the input to the counter might be
either a 10 MHz signal or two 1 pps signals from a variety of oscillators,
depending on whether I am doing frequency or time interval measurements)?
Initially I thought it would be best to match the impedances (in which case
I should be using 50 ohm), but now I am not so sure.

When I tried to read up on it, I found there is a lot of conflicting
information out there. I trust the Agilent Application Note 200
(Fundamentals of Electronic Counters)  and it says "for frequencies up to
10 MHz an input of 1 mega ohm is usually preferred". However, the same
document also states that "the higher the impedance the more susceptible to
noise and false counts the counter becomes". And could there possibly be a
problem with reflections if the impedances aren't matched?

If anyone out there has a good handle on this sort of stuff and can provide
me with some advice, it would be greatly appreciated.

Thanks.

Belinda
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Re: [time-nuts] Impedance question

[Tom Holmes]

Belinda...

In general you want to have the impedances matched in order to keep the
waveforms clean. What that implies is that you have to know the source
impedance as well as the load impedance. Not all sources are 50 ohms, it
seems, so some homework is in order to be successful. 

Tom Holmes, N8ZM

-Original Message-
From: time-nuts  On Behalf Of SimBeej
Sent: Monday, September 07, 2020 8:04 PM
To: time-nuts@lists.febo.com
Subject: [time-nuts] Impedance question

Dear fellow Time-Nuts,

I have a question about impedance matching (and I apologise in advance for
my blatant ignorance on this matter, but I don't have a background in
electronics and hardware, so am having to learn along the way).

When using frequency counters (in my case a 53230A and SR620) for making
frequency or time interval measurements, should I be choosing 50 ohm for 1
mega ohm as the input impedance (where the input to the counter might be
either a 10 MHz signal or two 1 pps signals from a variety of oscillators,
depending on whether I am doing frequency or time interval measurements)?
Initially I thought it would be best to match the impedances (in which case
I should be using 50 ohm), but now I am not so sure.

When I tried to read up on it, I found there is a lot of conflicting
information out there. I trust the Agilent Application Note 200
(Fundamentals of Electronic Counters)  and it says "for frequencies up to
10 MHz an input of 1 mega ohm is usually preferred". However, the same
document also states that "the higher the impedance the more susceptible to
noise and false counts the counter becomes". And could there possibly be a
problem with reflections if the impedances aren't matched?

If anyone out there has a good handle on this sort of stuff and can provide
me with some advice, it would be greatly appreciated.

Thanks.

Belinda
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Re: [time-nuts] Impedance question

[Bob kb8tq]

Hi

You actually have at least three components to your setup:

1) You have the *source* impedance of your signal

2) You have the impedance / length / loss / stability of the cable connecting 
the 
source to the load

3) You have the load impedance. 

In an ideal world, you would have cable that is truly 50 ohms at all 
frequencies. 
With that cable a 50 ohm termination at *either* end of the cable would absorb
all reflections. Either it is eliminated on hitting the load ( = load is 
matched) or
it is eliminated when it returns to the source ( = source is matched). Either 
way,
you have no ringing reflections. 

Indeed you often terminate *both* ends of the cable. That helps with cables that
may not *really* be 50 ohms. You get reflections reduced at both ends, so the
net is a bit better. 



In the case of a pure sine wave, things can be a bit “interesting”. Whatever the
impedances involved and whatever the cable impedance, it all works to a phase
shift and a loss. Loss is never a good thing. Phase shift (as long as it is 
perfectly
stable) is really not much of an issue. 

===

So what *is* your setup? 

PPS outputs may or may not be source matched. PPS outputs that are matched 
and running into a matched load result in logic levels that are 1/2 what you 
expected
them to be ( = you have a 2;1 attenuator). Normally PPS is matched at one end 
*or*
the other, but not both.

Cable length can matter. A 1 KM cable is a very different thing than a 1 M 
cable. 
Generally if the cable is < 1/10 the wavelength of the signal ( 10 MHz has a 30 
M 
wavelength) the cable is better treaded as lumped elements than with 
transmission 
line equations. The typical cables normally used tend to fall into this ( < 3 
M) range. 

Yes, this can go on and on …..

Lots of fun !!

Bob 

> On Sep 7, 2020, at 8:03 PM, SimBeej  wrote:
> 
> Dear fellow Time-Nuts,
> 
> I have a question about impedance matching (and I apologise in advance for
> my blatant ignorance on this matter, but I don't have a background in
> electronics and hardware, so am having to learn along the way).
> 
> When using frequency counters (in my case a 53230A and SR620) for making
> frequency or time interval measurements, should I be choosing 50 ohm for 1
> mega ohm as the input impedance (where the input to the counter might be
> either a 10 MHz signal or two 1 pps signals from a variety of oscillators,
> depending on whether I am doing frequency or time interval measurements)?
> Initially I thought it would be best to match the impedances (in which case
> I should be using 50 ohm), but now I am not so sure.
> 
> When I tried to read up on it, I found there is a lot of conflicting
> information out there. I trust the Agilent Application Note 200
> (Fundamentals of Electronic Counters)  and it says "for frequencies up to
> 10 MHz an input of 1 mega ohm is usually preferred". However, the same
> document also states that "the higher the impedance the more susceptible to
> noise and false counts the counter becomes". And could there possibly be a
> problem with reflections if the impedances aren't matched?
> 
> If anyone out there has a good handle on this sort of stuff and can provide
> me with some advice, it would be greatly appreciated.
> 
> Thanks.
> 
> Belinda
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> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com
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[time-nuts] Impedance question

[SimBeej]

Dear fellow Time-Nuts,

I have a question about impedance matching (and I apologise in advance for
my blatant ignorance on this matter, but I don't have a background in
electronics and hardware, so am having to learn along the way).

When using frequency counters (in my case a 53230A and SR620) for making
frequency or time interval measurements, should I be choosing 50 ohm for 1
mega ohm as the input impedance (where the input to the counter might be
either a 10 MHz signal or two 1 pps signals from a variety of oscillators,
depending on whether I am doing frequency or time interval measurements)?
Initially I thought it would be best to match the impedances (in which case
I should be using 50 ohm), but now I am not so sure.

When I tried to read up on it, I found there is a lot of conflicting
information out there. I trust the Agilent Application Note 200
(Fundamentals of Electronic Counters)  and it says "for frequencies up to
10 MHz an input of 1 mega ohm is usually preferred". However, the same
document also states that "the higher the impedance the more susceptible to
noise and false counts the counter becomes". And could there possibly be a
problem with reflections if the impedances aren't matched?

If anyone out there has a good handle on this sort of stuff and can provide
me with some advice, it would be greatly appreciated.

Thanks.

Belinda
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[time-nuts] Quartzlock E10-MRX

[Arthur Dent]

I have a Quartzlock 3 that was an OCXO based 10Mhz standard.

It has a really nice distribution amp so I replaced the OCXO with

an LPRO-101 and added a fan. The switching power supply is

external. I’m sure some will cringe with the thought of a fan in

the enclosure but it works really well and is quiet. I added a fine

adjustment and a test BNC 10Mhz jack to the front panel.



https://oi906.photobucket.com/albums/ac262/rjb1998/Inside_zpskowa2fvj.jpg



https://img.photobucket.com/albums/ac262/rjb1998/Front_zpsiwxnlizx.jpg


-Arthur
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[time-nuts] Nortel Trimble NTBW50AA

[Jimmy Burrell]

Dear Time Nuts,

I have decided to part with my Nortel/Trimble GPS Receiver / GPSDO. This is a 
so called “cousin to the Thunderbolt”. tvb took a look at these and did some 
testing a while back. You can see his results in the form of lots of pretty 
graphs here: http://www.leapsecond.com/pages/nortel 


I’ve made a home-brew power cable and bought a power supply from digikey. These 
are included along with two BNC style pigtails. The unit plays nice with Lady 
Heather via rs232.

I’ve got it posted on over on everyone’s favorite fleabay site :)

https://www.ebay.com/itm/114396615550 

Please let me know if you have questions.

King Regards,

Jimmy…
N5SPE
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Re: [time-nuts] 5 Digit Panel meters

[Tim Shoppa]

This all probably belongs on volt-nuts not here. But 16 bit ADS1115’s are 
common as dirt for a few bucks and will yield most of 5 digits of monotonic 
non-skipping counts.

The internal reference and programmable gain of the ADS1115 is 0.1% ballpark. 
So any implication that all 5 digits are accurate is of course bogus. It still 
is useful for a lot of high dynamic range applications that we used to do with 
log detectors.

Tim N3QE

> On Sep 7, 2020, at 1:21 PM, Bob kb8tq  wrote:
> 
> Hi
> 
> So, *assuming* there is no other ADC on the board ….
> 
> DC performance of the STM8 ADC’s is somewhere in the 8 to 9 bit range as far
> as ENOB with significant averaging. For the sake of simplicity, let’s say 
> they *do*
> make it to 10 bits. 
> 
> But … do we get the 10 bits?
> 
> The range on the meter is 33V. The reference to the DAC is (likely) 5V. You 
> just lost
> nearly 3 bits from that scale mismatch.  At the 5V level, you would be 
> running just over
> 7 of your (ideal) 10 bits. 
> 
> Net result is that you are trying to check a 16 bit gizmo with a not quite 8 
> bit device.
> 
> Bob
> 
>> On Sep 7, 2020, at 10:01 AM, DM  wrote:
>> 
>> I must caution all who would buy the 5-digit panel meters, thinking that 
>> they are actually capable of accuracy that you would normally expect from a 
>> 5-digit meter. 
>> The panel meters in question use a STM8S003F3 micro-controller, which 
>> contains a single 10-bit A/D. Depending on which eBay or AliExpress listing 
>> you look at, accuracy varies from 0.3% to 0.05%. 
>> Make your own deductions from this info, just be aware that all is not what 
>> you might expect of this cheap little meter. 
>> 
>> Cheers, 
>> Dave M 
>> 
>> 
>> From: "Perry Sandeen via time-nuts"  
>> To: time-nuts@lists.febo.com 
>> Cc: "Perry Sandeen"  
>> Sent: Monday, September 7, 2020 12:20:12 AM 
>> Subject: [time-nuts] 5 Digit Panel meters 
>> 
>> Learned List, 
>> From the on and off list comments I've received I realize that I didn't 
>> provide a fuller explanation of my proposed idea for this I apologize. 
>> What I was proposing was to try and use the tiny panel meters fount on ebay 
>> when you use the category listed as *Digital Panel Meters*. One listing 
>> number is 203076543505. Measurement range: DC: 0.000-33.000V. for $3.83 plus 
>> free shipping. This is just one of many listings for similar items. As I 
>> stated in my original post, I have no idea if they are accurate, stable or 
>> suitable to what I proposed. 
>> Some of the replies mentioned temperature drift and other potential problems 
>> which may make then unsuitable for my idea. This was to measure three 
>> different voltages simultaneously and see if there was some useful 
>> correlation in the readings. 
>> This is an experimental concept idea which may or may not be 
>> useful..Sometimes these ideas work or we learn to go to plan *B, C, or D* 
>> Because of the low cost i felt that this might a useful idea. Others with 
>> more experience of these voltages and how much they do or do not change may 
>> judge my idea as impracticable. 
>> That's fine. 
>> 
>> I learn from the list comments and I'd rather hear that it's not a good idea 
>> from the members before spending the money and effort. 
>> I do have a Fluke/Phillips 6.5 for making precise reading when needed. 
>> 
>> Regards, 
>> Perrier 
>> 
>> 
>> 
>> 
>> ___ 
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> 
> 
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Re: [time-nuts] 5 Digit Panel meters

[Bob kb8tq]

Hi

So, *assuming* there is no other ADC on the board ….

DC performance of the STM8 ADC’s is somewhere in the 8 to 9 bit range as far
as ENOB with significant averaging. For the sake of simplicity, let’s say they 
*do*
make it to 10 bits. 

But … do we get the 10 bits?

The range on the meter is 33V. The reference to the DAC is (likely) 5V. You 
just lost
nearly 3 bits from that scale mismatch.  At the 5V level, you would be running 
just over
7 of your (ideal) 10 bits. 

Net result is that you are trying to check a 16 bit gizmo with a not quite 8 
bit device.

Bob

> On Sep 7, 2020, at 10:01 AM, DM  wrote:
> 
> I must caution all who would buy the 5-digit panel meters, thinking that they 
> are actually capable of accuracy that you would normally expect from a 
> 5-digit meter. 
> The panel meters in question use a STM8S003F3 micro-controller, which 
> contains a single 10-bit A/D. Depending on which eBay or AliExpress listing 
> you look at, accuracy varies from 0.3% to 0.05%. 
> Make your own deductions from this info, just be aware that all is not what 
> you might expect of this cheap little meter. 
> 
> Cheers, 
> Dave M 
> 
> 
> From: "Perry Sandeen via time-nuts"  
> To: time-nuts@lists.febo.com 
> Cc: "Perry Sandeen"  
> Sent: Monday, September 7, 2020 12:20:12 AM 
> Subject: [time-nuts] 5 Digit Panel meters 
> 
> Learned List, 
> From the on and off list comments I've received I realize that I didn't 
> provide a fuller explanation of my proposed idea for this I apologize. 
> What I was proposing was to try and use the tiny panel meters fount on ebay 
> when you use the category listed as *Digital Panel Meters*. One listing 
> number is 203076543505. Measurement range: DC: 0.000-33.000V. for $3.83 plus 
> free shipping. This is just one of many listings for similar items. As I 
> stated in my original post, I have no idea if they are accurate, stable or 
> suitable to what I proposed. 
> Some of the replies mentioned temperature drift and other potential problems 
> which may make then unsuitable for my idea. This was to measure three 
> different voltages simultaneously and see if there was some useful 
> correlation in the readings. 
> This is an experimental concept idea which may or may not be 
> useful..Sometimes these ideas work or we learn to go to plan *B, C, or D* 
> Because of the low cost i felt that this might a useful idea. Others with 
> more experience of these voltages and how much they do or do not change may 
> judge my idea as impracticable. 
> That's fine. 
> 
> I learn from the list comments and I'd rather hear that it's not a good idea 
> from the members before spending the money and effort. 
> I do have a Fluke/Phillips 6.5 for making precise reading when needed. 
> 
> Regards, 
> Perrier 
> 
> 
> 
> 
> ___ 
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Re: [time-nuts] 5 Digit Panel meters

[Bob kb8tq]

Hi

Measurement accuracy as stated in the listing is 0.3% or 3,000 ppm. Some 
listings call it out
as 0.3% +/- 2 LSD.  Since they removed the markings from some of the chips, 
figuring out exactly 
what’s in there could be a bit exciting.  

Full scale is 33V so the full range display would be 33.000 . The LSD is 1 mv 
so +/- 2 LSD would
be +/- 2 MV. 

We are looking for 5 / 2^16 volts. That’s 76 uV. Ten DAC LSB’s still don’t get 
you to 1 mv. 

I’d bet the target audience for these meters are some sort of 24V battery 
setup. The voltage 
range would make sense in that case. 

Bob


> On Sep 7, 2020, at 1:20 AM, Perry Sandeen via time-nuts 
>  wrote:
> 
> 203076543505

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Re: [time-nuts] 5 Digit Panel meters

[DM]

I must caution all who would buy the 5-digit panel meters, thinking that they 
are actually capable of accuracy that you would normally expect from a 5-digit 
meter. 
The panel meters in question use a STM8S003F3 micro-controller, which contains 
a single 10-bit A/D. Depending on which eBay or AliExpress listing you look at, 
accuracy varies from 0.3% to 0.05%. 
Make your own deductions from this info, just be aware that all is not what you 
might expect of this cheap little meter. 

Cheers, 
Dave M 


From: "Perry Sandeen via time-nuts"  
To: time-nuts@lists.febo.com 
Cc: "Perry Sandeen"  
Sent: Monday, September 7, 2020 12:20:12 AM 
Subject: [time-nuts] 5 Digit Panel meters 

Learned List, 
>From the on and off list comments I've received I realize that I didn't 
>provide a fuller explanation of my proposed idea for this I apologize. 
What I was proposing was to try and use the tiny panel meters fount on ebay 
when you use the category listed as *Digital Panel Meters*. One listing number 
is 203076543505. Measurement range: DC: 0.000-33.000V. for $3.83 plus free 
shipping. This is just one of many listings for similar items. As I stated in 
my original post, I have no idea if they are accurate, stable or suitable to 
what I proposed. 
Some of the replies mentioned temperature drift and other potential problems 
which may make then unsuitable for my idea. This was to measure three different 
voltages simultaneously and see if there was some useful correlation in the 
readings. 
This is an experimental concept idea which may or may not be useful..Sometimes 
these ideas work or we learn to go to plan *B, C, or D* 
Because of the low cost i felt that this might a useful idea. Others with more 
experience of these voltages and how much they do or do not change may judge my 
idea as impracticable. 
That's fine. 

I learn from the list comments and I'd rather hear that it's not a good idea 
from the members before spending the money and effort. 
I do have a Fluke/Phillips 6.5 for making precise reading when needed. 

Regards, 
Perrier 




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[time-nuts] 5 Digit Panel meters

[Perry Sandeen via time-nuts]

Learned List,
From the on and off list comments I've received I realize that I didn't provide 
a fuller explanation of my proposed idea for this I apologize.
What I was proposing was to try and use the tiny panel meters fount on ebay 
when you use the category listed as *Digital Panel Meters*. One listing number 
is 203076543505.  Measurement range: DC: 0.000-33.000V. for $3.83 plus free 
shipping.  This is just one of many listings for similar items.  As I stated in 
my original post, I have no idea if they are accurate, stable or suitable to 
what I proposed.
Some of the replies mentioned temperature drift and other potential problems 
which may make then unsuitable for my idea.  This was to measure three 
different voltages simultaneously and see if there was some useful correlation 
in the readings.
This is an experimental concept idea which may or may not be useful..Sometimes 
these ideas work or we learn to go to plan *B, C, or D*
Because of the low cost i felt that this might a useful idea.  Others with more 
experience of these voltages and how much they do or do not change may judge my 
idea as impracticable.
That's fine.

I learn from the list comments and I'd rather hear that it's not a good idea 
from the members before spending the money and effort.
I do have a Fluke/Phillips 6.5 for making precise reading when needed.

Regards,
Perrier

  


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