Explain odd digital clock behavior?

Guest
Greetings All,
I have a digital clock that's at least 25 years old. I also have a
machine shop that uses a rotary phase converter to supply 3 phase
power to the machines, some of which are CNC. The clock is in my house
which is on the same property as my shop. Whenever I use certain CNC
machines the clock at home gains time. The shop and the house are both
fed power from the same pole xfmr. I think that the digital clock must
use the 60 HZ ac voltage for the time-keeping reference. And I think
that there must be harmonics or something similar coming from the CNC
machines that the clock is unable to filter out and that is why the
clock runs fast when the machines are running. Am I on the right
track? No other clocks in the house run fast and I'm not going to try
to fix the old clock, I just want to know what's going on.
Thanks,
Eric
 
<etpm@whidbey.com> wrote in message
news:4956e13f.2349268@news.whidbey.net...
Greetings All,
I have a digital clock that's at least 25 years old. I also have a
machine shop that uses a rotary phase converter to supply 3 phase
power to the machines, some of which are CNC. The clock is in my house
which is on the same property as my shop. Whenever I use certain CNC
machines the clock at home gains time. The shop and the house are both
fed power from the same pole xfmr. I think that the digital clock must
use the 60 HZ ac voltage for the time-keeping reference. And I think
that there must be harmonics or something similar coming from the CNC
machines that the clock is unable to filter out and that is why the
clock runs fast when the machines are running. Am I on the right
track? No other clocks in the house run fast and I'm not going to try
to fix the old clock, I just want to know what's going on.
Thanks,
Eric
Click to expand...

Yep, most plug-in-the-wall digiclocks use the line frequency to count time
because it's very accurate. Your CNC machine is probably distorting the line
voltage due to non-sinusoidal current draw by the machine and high source
impedance somewhere in your power feed.

Also, your clock isn't do a good job of ignoring non-monotonic line voltage
so it's multi clocking on each true waveform edge.

The best thing to do is to let me come take your CNC machine and I'll give
you a better clock in exchange. I've always wanted a CNC mill.

Bob
--
== All google group posts are automatically deleted due to spam ==
 
<etpm@whidbey.com
I have a digital clock that's at least 25 years old.
Click to expand...

** Is that an electronic clock ( with LED, LCD or a fluorescent display )
or a digital mechanical clock with numbered wheels or flip cards ??


I also have a
machine shop that uses a rotary phase converter to supply 3 phase
power to the machines, some of which are CNC. The clock is in my house
which is on the same property as my shop. Whenever I use certain CNC
machines the clock at home gains time. The shop and the house are both
fed power from the same pole xfmr. I think that the digital clock must
use the 60 HZ ac voltage for the time-keeping reference. And I think
that there must be harmonics or something similar coming from the CNC
machines that the clock is unable to filter out and that is why the
clock runs fast when the machines are running. Am I on the right
track? No other clocks in the house run fast and I'm not going to try
to fix the old clock, I just want to know what's going on.
Click to expand...

** Assuming you clock is of the electronic kind, my hunch is that the
neutral line is heavily contaminated with harmonic current pulses from the 3
phase supply.

If you owned a scope you could easily check the neutral voltage waveform in
the house for this.

Harmonic voltages on the neutral will create additional, false zero
crossings in the AC supply - and it is likely your clock is detecting zero
crossings to derive it's 60 Hz time base.




...... Phil
 
etpm@whidbey.com wrote:

Greetings All,
I have a digital clock that's at least 25 years old.
Click to expand...
Do you mean digital as in electronic or those clocks that had numbers that
flipped over mechanically ?

Graham
 
BobW wrote:

etpm@whidbey.com> wrote in message

Greetings All,
I have a digital clock that's at least 25 years old. I also have a
machine shop that uses a rotary phase converter to supply 3 phase
power to the machines, some of which are CNC. The clock is in my house
which is on the same property as my shop. Whenever I use certain CNC
machines the clock at home gains time. The shop and the house are both
fed power from the same pole xfmr. I think that the digital clock must
use the 60 HZ ac voltage for the time-keeping reference. And I think
that there must be harmonics or something similar coming from the CNC
machines that the clock is unable to filter out and that is why the
clock runs fast when the machines are running. Am I on the right
track? No other clocks in the house run fast and I'm not going to try
to fix the old clock, I just want to know what's going on.
Thanks,
Eric

Yep, most plug-in-the-wall digiclocks use the line frequency to count time
because it's very accurate. Your CNC machine is probably distorting the line
voltage due to non-sinusoidal current draw by the machine and high source
impedance somewhere in your power feed.

Also, your clock isn't do a good job of ignoring non-monotonic line voltage
so it's multi clocking on each true waveform edge.

The best thing to do is to let me come take your CNC machine and I'll give
you a better clock in exchange. I've always wanted a CNC mill.
Click to expand...
I understand your sentiments on that point !

However, given the tiny amount of power required, a simple LC or even RC filter
in the supply might fix it.

Graham
 
On Sat, 27 Dec 2008 18:38:27 -0800, "BobW"
<nimby_GIMME_SOME_SPAM@roadrunner.com> wrote:

etpm@whidbey.com> wrote in message
news:4956e13f.2349268@news.whidbey.net...
Greetings All,
I have a digital clock that's at least 25 years old. I also have a
machine shop that uses a rotary phase converter to supply 3 phase
power to the machines, some of which are CNC. The clock is in my house
which is on the same property as my shop. Whenever I use certain CNC
machines the clock at home gains time. The shop and the house are both
fed power from the same pole xfmr. I think that the digital clock must
use the 60 HZ ac voltage for the time-keeping reference. And I think
that there must be harmonics or something similar coming from the CNC
machines that the clock is unable to filter out and that is why the
clock runs fast when the machines are running. Am I on the right
track? No other clocks in the house run fast and I'm not going to try
to fix the old clock, I just want to know what's going on.
Thanks,
Eric


Yep, most plug-in-the-wall digiclocks use the line frequency to count time
because it's very accurate. Your CNC machine is probably distorting the line
voltage due to non-sinusoidal current draw by the machine and high source
impedance somewhere in your power feed.

Also, your clock isn't do a good job of ignoring non-monotonic line voltage
so it's multi clocking on each true waveform edge.

The best thing to do is to let me come take your CNC machine and I'll give
you a better clock in exchange. I've always wanted a CNC mill.

Bob
--
== All google group posts are automatically deleted due to spam ==


Greetings Bob,
Click to expand...
If you can carry the CNC out of the shop yourself then I'll do the
trade. Mind you, there are a few obstacles that you will need to lift
the machine over. But if you can clean and jerk 5000 lbs then I guess
you could just get the machine anytime without my permission.
Eric
 
On Sun, 28 Dec 2008 12:09:05 +0000, Eeyore
<rabbitsfriendsandrelations@hotmail.com> wrote:

etpm@whidbey.com wrote:

Greetings All,
I have a digital clock that's at least 25 years old.

Do you mean digital as in electronic or those clocks that had numbers that
flipped over mechanically ?

Graham

Greetings Graham,
Click to expand...
I should have said it was the type with an electronic (LED in this
case) display, not mechanical.
Cheers,
Eric
 
On Sun, 28 Dec 2008 20:41:08 +0000, etpm wrote:
On Sat, 27 Dec 2008 18:38:27 -0800, "BobW"
etpm@whidbey.com> wrote in message
news:4956e13f.2349268@news.whidbey.net...
Greetings All,
I have a digital clock that's at least 25 years old. I also have a
machine shop that uses a rotary phase converter to supply 3 phase power
to the machines, some of which are CNC. The clock is in my house which
is on the same property as my shop. Whenever I use certain CNC machines
the clock at home gains time. The shop and the house are both fed power
from the same pole xfmr. I think that the digital clock must use the 60
HZ ac voltage for the time-keeping reference. And I think that there
must be harmonics or something similar coming from the CNC machines
that the clock is unable to filter out and that is why the clock runs
fast when the machines are running. Am I on the right track? No other
clocks in the house run fast and I'm not going to try to fix the old
clock, I just want to know what's going on. Thanks,

Yep, most plug-in-the-wall digiclocks use the line frequency to count
time because it's very accurate. Your CNC machine is probably distorting
the line voltage due to non-sinusoidal current draw by the machine and
high source impedance somewhere in your power feed.

Also, your clock isn't do a good job of ignoring non-monotonic line
voltage so it's multi clocking on each true waveform edge.

The best thing to do is to let me come take your CNC machine and I'll
give you a better clock in exchange. I've always wanted a CNC mill.

Greetings Bob,
If you can carry the CNC out of the shop yourself then I'll do the trade.
Mind you, there are a few obstacles that you will need to lift the machine
over. But if you can clean and jerk 5000 lbs then I guess you could just
get the machine anytime without my permission. Eric
Click to expand...
Got a pallet jack? ;-p

Cheers!
Rich
 
On Sun, 28 Dec 2008 20:42:33 +0000, etpm wrote:
On Sun, 28 Dec 2008 12:09:05 +0000, Eeyore
etpm@whidbey.com wrote:

Greetings All,
I have a digital clock that's at least 25 years old.

Do you mean digital as in electronic or those clocks that had numbers
that flipped over mechanically ?

Greetings Graham,
I should have said it was the type with an electronic (LED in this case)
display, not mechanical.
Cheers,
Eric
Click to expand...
It's very likely line harmonics from the 3-phase converter, overclocking
the clock.

If the clock is important to you, you could add a crystal osc. and
counter chain to give you a decent 60Hz pulse stream.

Good Luck!
Rich
 
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