Fast clock- ferrite ring

[Hv&Lv]

Why is this a power company problem at all? Sounds more like an appliance problem (get the clock panels replaced). Or did it move into the finger-pointing stage.

finger pointing, and it’s two clocks. The rest are radio calibrated.
My first suggestion was to buy them two clocks until I found out one of them is in with the new stove.
I then went the 50 hz route as Larry suggested, until two clocks came into play.
Sending service guys out now to check on all connections. This is one house on a tap by themselves.

I’ve put a PQM on there to register flicker, but my limits won’t go low enough to capture anything.

 

[Hv&Lv]

As hbiss says, the schmidt trigger would be part of an ic clock chip, not a stand alone component.

I think it could be 'bad', in the sense of a poor design with inadequate filtering, or with insufficient hysteresis, or with defective filter components. Something that is functional in most situations but noise sensitive.

And to echo Speedskater: we don't know that these clocks are mains synchronized. Because of available chips many modern clocks do use mains as their frequency standard but many do not.

Jon

I remember a paper I have somewhere back from the 90s that addressed this. I’m trying to find it in a few computers.
It addressed this issue to some extent. Can’t quite remember..
But the mention of a Schmidt trigger got me going and it hit me last night in bed about this paper..

 

[WasGSOHM]

What I’m getting is “minutes a day”..

after the suggestions received this far I’m going to have them give me a weeks worth of times.

Yeah. Can of worms, iffy outcome.

 

[synchro]

Perhaps the customers are sometimes using a mixer, blender, electric knife, etc. that has a universal motor with brushes and it's generating conducted interference that causes false triggering of the clock. If such an appliance is being plugged into the same branch circuit as the stove then that would make this scenario more likely.

A suggested experiment is to plug in a power tool (drill, saw, etc.) that has a universal motor on the clock's branch circuit and see if it has an effect on the clock. Larger and older power tools would be a worst case test.

 

[Hv&Lv]

Perhaps the customers are sometimes using a mixer, blender, electric knife, etc. that has a universal motor with brushes and it's generating conducted interference that causes false triggering of the clock. If such an appliance is being plugged into the same branch circuit as the stove then that would make this scenario more likely.

A suggested experiment is to plug in a power tool (drill, saw, etc.) that has a universal motor on the clock's branch circuit and see if it has an effect on the clock. Larger and older power tools would be a worst case test.

I believe that’s my next step as I have found the paper I was looking for.
Get my O scope connected and see what’s going on.

 

[Hv&Lv]

Pretty good little paper here.

 

[WasGSOHM]

Get my O scope connected and see what’s going on.

I hope it is not susceptible to RFI/EMI.
With a radio tower some distance away you can see the carrier freq and the modulation on the trace, it showed up as a blurry, thick trace.

 

[kwired]

Perhaps the customers are sometimes using a mixer, blender, electric knife, etc. that has a universal motor with brushes and it's generating conducted interference that causes false triggering of the clock. If such an appliance is being plugged into the same branch circuit as the stove then that would make this scenario more likely.

A suggested experiment is to plug in a power tool (drill, saw, etc.) that has a universal motor on the clock's branch circuit and see if it has an effect on the clock. Larger and older power tools would be a worst case test.

won't that take quite a bit of operation time before you notice the clock is off?

I'd think the problem here is clock is significantly off in somewhat short time period, like it gains a couple minutes in a week where these appliances maybe only cause up to couple minutes in a year.

 

[gadfly56]

How fast is fast? Could the stove be designed for 50 Hz?

This seems unlikely. At a 60/50 ratio, the clock would be gaining a minute every 5 true minutes and 12 minutes every true hour. In 24 true hours, the clock would be 4 hours and 48 minutes ahead. The OP said the delta is "minutes per day".

 

[winnie]

Very interesting little paper. The line about the _optional_ RC filter on the clock sense line suggests that some production designs will be more or less sensitive to the noise being discussed. Also the potential noise sources suggest that far from being a nuisance problem of cheap clocks, it may be worth investigating the source of the noise. ( I presume arcing distribution switch gear is something you want to discover when the problem is relatively minor...)

-Jon

 

[synchro]

won't that take quite a bit of operation time before you notice the clock is off?

I'd think the problem here is clock is significantly off in somewhat short time period, like it gains a couple minutes in a week where these appliances maybe only cause up to couple minutes in a year.

Digital logic is extremely fast and so the decade counters could move very quickly on higher frequency noise, and so it depends on how effective any filtering or other line signal conditioning is in removing such noise (assuming there is any).
But I agree that the problem could very likely be something else, especially if the clock does not move in bursts but is advancing on a relatively consistent basis.
I think it would still be worthwhile do a test with a universal motor just to see if the clock is susceptible to noise, because if it was sensititive to this then it would likely be effected by POCO noise as well.

 

[hbiss]

Digital logic is extremely fast and so the decade counters could move very quickly on higher frequency noise, and so it depends on how effective any filtering or other line signal conditioning is in removing such noise (assuming there is any).

I'm assuming there isn't. Cheap design. Line noise and dirty power is nothing out of the ordinary and 99% of other clocks out there seem to deal with is just fine.

-Hal