DM42- clock losing time

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ctrclckws
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Re: DM42- clock losing time

Post by ctrclckws » Fri May 10, 2019 7:57 pm

Received my DM42 in August of 2018 so it's pretty new S/N 3108.
No real issues with time keeping.
So maybe the design has been tweaked in more recent batches?

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Walter
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Re: DM42- clock losing time

Post by Walter » Fri May 10, 2019 9:08 pm

Jebem wrote:
Fri May 10, 2019 6:04 pm
I don't remember to see any adverts from the manufacturer concerning the precision of the clock but i might be wrong.
Nor do I. Though it's not a matter of specification or advertising, it's just a matter of customer expectation. If and when you include something like an RTC in a calculator nowadays, a customer will expect it showing the real time. And this may be off for seconds but not for minutes IMHO.

ctrclckws wrote:
Fri May 10, 2019 7:57 pm
Received my DM42 in August of 2018 so it's pretty new S/N 3108.
No real issues with time keeping.
So maybe the design has been tweaked in more recent batches?
Maybe. But one correct device may be a lucky chance hit as well. Nobody knows but SM.
DM42 SN: 00041 --- Follower of Platon.

HP-35, HP-45, ..., HP-50, WP 34S, WP 31S, DM16L

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TwoWeims
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Re: DM42- clock losing time

Post by TwoWeims » Fri May 10, 2019 11:44 pm

I tune my HF rig to WWV and let my DM42 listen to it over night... :lol:

You just have to inject some humor into this very serious discussion.
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cappy
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Re: DM42- clock losing time

Post by cappy » Sat May 11, 2019 3:43 am

TwoWeims wrote:
Fri May 10, 2019 11:44 pm
I tune my HF rig to WWV and let my DM42 listen to it over night... :lol:

You just have to inject some humor into this very serious discussion.
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cappy
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Re: DM42- clock losing time

Post by cappy » Sat May 11, 2019 3:45 am

ctrclckws wrote:
Fri May 10, 2019 7:57 pm
Received my DM42 in August of 2018 so it's pretty new S/N 3108.
No real issues with time keeping.
So maybe the design has been tweaked in more recent batches?
In my case, it lost time while the dm42 wasn’t in use.
It may be something to do when the calc is turned off as opposed to being used very often.
DM42 SN: 0612

ctrclckws
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Re: DM42- clock losing time

Post by ctrclckws » Sat May 11, 2019 8:22 am

Mine is also mostly in my work bag, waiting for its time in the sun.

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Jebem
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Re: DM42- clock losing time

Post by Jebem » Sat May 11, 2019 7:03 pm

Walter wrote:
Fri May 10, 2019 9:08 pm
Jebem wrote:
Fri May 10, 2019 6:04 pm
I don't remember to see any adverts from the manufacturer concerning the precision of the clock but i might be wrong.
Nor do I. Though it's not a matter of specification or advertising, it's just a matter of customer expectation. If and when you include something like an RTC in a calculator nowadays, a customer will expect it showing the real time. And this may be off for seconds but not for minutes IMHO.
I see you point.

However the installed crystal features 20ppm, resulting in around 60 seconds per month drift.
So the worst case scenario for the reported clock issues should be around 6 minutes after 6 months.
Crystal tolerances and temperature variations explain the other better looking reported values.

To have a proper precise RTC significant effort and cost would be required during the design stage, starting with very stable and expensive components selection (crystal and load components like capacitors and resistors) .

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Walter
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Re: DM42- clock losing time

Post by Walter » Sat May 11, 2019 9:03 pm

OK, 20ppm corresponds to 10.5 minutes per year (that's far worse than any cheap quartz watch sold nowadays). But now we must talk about the 20ppm - how do you get them?
  1. Are these crystals produced according to this spec in an industrial process? I hope so. Then, to warrant almost all crystals meeting this spec, standard deviation (desvio padral) of the production process (following a normal distribution) shall be less than 20ppm/6 = 3.3ppm. The crystals would come out distributed with 95% or more of them between -10 and +10ppm.
  2. If, OTOH, these crystals are picked out of a population having a significantly greated SD (due to a less precisely controlled production process), you'd need a sorting machine featuring a precision of ~1.3ppm and expect the crystal accuracy being uniformly distributed between -20 and +20ppm.
Finding out more about it would require some time accuracy statistics: how many DM42 show which deviation from real time?
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Jebem
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Re: DM42- clock losing time

Post by Jebem » Sat May 11, 2019 10:48 pm

Walter wrote:
Sat May 11, 2019 9:03 pm
OK, 20ppm corresponds to 10.5 minutes per year (that's far worse than any cheap quartz watch sold nowadays). But now we must talk about the 20ppm - how do you get them?
These are regular electronics components found in shops. Nothing fancing like the ones used in professional and lab equipments where the oscillator is temperature controlled and tolerances are tight.

Some time ago i created a thread in the other forum where i tried to detail the hardware components used in the DM42. I have used a picture posted by someone in the net and the crystal chip is clearly visible. By checking the crystal specifications from the reference code printed on the chip Q1 we kniw it is a 20ppm component:

https://www.hpmuseum.org/forum/thread-1 ... light=Dm42


20ppm on a crystal is just the regular low precision part. 10ppm or less will be more expensive.
But as i said, the precision is not only dependent on this component. The load circuit is critical to maintain the oscillator frequency as close as possible to the specification. For instance, bad quality capacitors will cause frequency deviation with temperature.

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Walter
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Re: DM42- clock losing time

Post by Walter » Sun May 12, 2019 6:28 am

Bom dia Jose, y muito obrigado for pointing to your comprehensive investigation. I admit I've read it a year ago but didn't remember. BTW, please note you called the quartz a "high precision crystal" in your post of 2018-02-11 and didn't relativize this statement any later AFAICS.
DM42 SN: 00041 --- Follower of Platon.

HP-35, HP-45, ..., HP-50, WP 34S, WP 31S, DM16L

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