Annoying Clock on Microwave

J

jeff_wisnia

Guest
From my "I can't believe they'd make it this way" list.

Last year I purchased a new Westinghouse Model WST-3501 microwave oven
for our office lunchroom.

It heats and cooks things fine, but has one lousy feature which I can't
avoid noticing and which irks me very time I see it.

The TOD, which is displayed whenever the unit is on standby, loses about
two minutes a day, and has to be reset every few days to keep from
falling ridiculously behind.

I'm shocked, shocked, that the clock isn't synced to the 120 volt 60 Hz
power the unit runs on, like every other line powered appliance with a
digital TOD display I own.

The only reason I can guess for the poor timekeeping is that the
circuitry/board running the clock is used on their 220 volt 50 Hz
versions without modification, so the makers decided not to use line
sync for the clock, and probably didn't want to spring for a crystal
oscillator either, so used an RC one instead.

I tried emailing Westinghouse about this and they fobbed me off to a
subsidiary who couldn't even bother to respond to an email.

Thanks for reading. Anyone got any other ideas about why the stupid
clock in this microwave loses time?

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.
 
The only reason I can guess for the poor timekeeping is that the
circuitry/board running the clock is used on their 220 volt 50 Hz
versions without modification, so the makers decided not to use
line sync for the clock, and probably didn't want to spring for
a crystal oscillator either, so used an RC one instead.
Click to expand...
A chip would likely be designed to work at either frequency, with a jumper
making the selection.
 
On Friday, April 22, 2011 10:35:47 AM UTC-7, jeff_wisnia wrote:
From my "I can't believe they'd make it this way" list.

Last year I purchased a new Westinghouse Model WST-3501 microwave oven
for our office lunchroom.

The TOD, which is displayed whenever the unit is on standby, loses about
two minutes a day, and has to be reset every few days
Click to expand...
Check your outlet! It sounds like some considerable voltage drop
occurs in the wiring and the clock stops during operation.
I've seen a microwave gain seconds when in use, too (the
TTL chips in the clock circuitry had no bypass capacitors).
 
whit3rd wrote:
On Friday, April 22, 2011 10:35:47 AM UTC-7, jeff_wisnia wrote:

From my "I can't believe they'd make it this way" list.

Last year I purchased a new Westinghouse Model WST-3501 microwave oven
for our office lunchroom.


The TOD, which is displayed whenever the unit is on standby, loses about
two minutes a day, and has to be reset every few days


Check your outlet! It sounds like some considerable voltage drop
occurs in the wiring and the clock stops during operation.
I've seen a microwave gain seconds when in use, too (the
TTL chips in the clock circuitry had no bypass capacitors).
Click to expand...

I doubt if it's voltage drop because the clock loses about 6 minutes
over a three day (holiday) weekend when no one is there using the microwave.

Also, FWIW, a complete power drop out and recovery causes the clock to
start at 12:00.

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.
 
Some years back our group designed a micro controller
project that used AC line zero cross for phase triggering.
Click to expand...
Did it work by looking for a polarity change, or near-zero voltage? If the
latter, line noise might cause it to miss some zero crossings, and the clock
would run slow.
 
On Apr 22, 10:35 am, jeff_wisnia <jwisniaDumpThisP...@conversent.net>
wrote:
 From my "I can't believe they'd make it this way" list.

Last year I purchased a new Westinghouse Model WST-3501 microwave oven
for our office lunchroom.

It heats and cooks things fine, but has one lousy feature which I can't
avoid noticing and which irks me very time I see it.

The TOD, which is displayed whenever the unit is on standby, loses about
two minutes a day, and has to be reset every few days to keep from
falling ridiculously behind.

I'm shocked, shocked, that the clock isn't synced to the 120 volt 60 Hz
power the unit runs on, like every other line powered appliance with a
digital TOD display I own.

The only reason I can guess for the poor timekeeping is that the
circuitry/board running the clock is used on their 220 volt 50 Hz
versions without modification, so the makers decided not to use line
sync for the clock, and probably didn't want to spring for a crystal
oscillator either, so used an RC one instead.

I tried emailing Westinghouse about this and they fobbed me off to a
subsidiary who couldn't even bother to respond to an email.

Thanks for reading. Anyone got any other ideas about why the stupid
clock in this microwave loses time?

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.
Click to expand...
Yes but some years back our group designed a micro controller project
that used AC line zero cross for phase triggering. Making that
controller into a clock and using 50 or 60 Hz as timing reference
would be as easy for them as it was for us. So THAT isn't a valid
excuse.

G˛
 
jeff_wisnia wrote:

I'm shocked, shocked, that the clock isn't synced to the 120 volt 60 Hz
power the unit runs on, like every other line powered appliance with a
digital TOD display I own.

The only reason I can guess for the poor timekeeping is that the
circuitry/board running the clock is used on their 220 volt 50 Hz
versions without modification, so the makers decided not to use line
sync for the clock, and probably didn't want to spring for a crystal
oscillator either, so used an RC one instead.
Click to expand...
I don't think this is a 50/60Hz issue. From the error rate you
describe, it should run faster not slower, and by a larger margin too.

Regardless, locking your clock to mains is not always a great idea.
Some areas are just plain wrong. I have a mains locked clock here that
loses a minute every week or so.
I have cheap non temperature compensated crystal locked clocks that are
by far superior to that.

The answer is worse than that.

The clocks are built to a price, the cheapest possible price.

Consider this: A microwave oven doesn't need a clock at all, just a
timekeeper for timed cooking. Accuracy is not a priority here at all.
The fact they have clocks at all means the manufacturers wanted to get
one leg up on the competitors without expending any money.

We're not talking cameras in cellphones here, there is NO reason for
them to make their clocks accurate, because non of the competition are
going to bother either.
--
To err is human. To moo bovine
 
On 22/04/2011 18:35, jeff_wisnia wrote:
From my "I can't believe they'd make it this way" list.

Last year I purchased a new Westinghouse Model WST-3501 microwave oven
for our office lunchroom.

It heats and cooks things fine, but has one lousy feature which I can't
avoid noticing and which irks me very time I see it.

The TOD, which is displayed whenever the unit is on standby, loses about
two minutes a day, and has to be reset every few days to keep from
falling ridiculously behind.

I'm shocked, shocked, that the clock isn't synced to the 120 volt 60 Hz
power the unit runs on, like every other line powered appliance with a
digital TOD display I own.

The only reason I can guess for the poor timekeeping is that the
circuitry/board running the clock is used on their 220 volt 50 Hz
versions without modification, so the makers decided not to use line
sync for the clock, and probably didn't want to spring for a crystal
oscillator either, so used an RC one instead.

I tried emailing Westinghouse about this and they fobbed me off to a
subsidiary who couldn't even bother to respond to an email.

Thanks for reading. Anyone got any other ideas about why the stupid
clock in this microwave loses time?
Click to expand...
Probably the clock is line sync'd, and then when cooking, is magnetron
supply sync'd - as critically voltage is lost at the connection point
where the clock takes its time period sample.

Try not cooking for a day and see if that fixes the time loss, then try
using a shorter or heavier cable for the line connection?

--
Adrian C
 
On 4/22/2011 10:27 PM John Tserkezis spake thus:

Consider this: A microwave oven doesn't need a clock at all, just a
timekeeper for timed cooking. Accuracy is not a priority here at all.
The fact they have clocks at all means the manufacturers wanted to get
one leg up on the competitors without expending any money.

We're not talking cameras in cellphones here, there is NO reason for
them to make their clocks accurate, because non of the competition are
going to bother either.
Click to expand...
True now, no doubt, but wasn't always so. My Magic Chef, which I got
used, lessee, 23 years ago or so and still works perfectly, has a very
accurate clock. Crystal-controlled, I'm going to guess.


--
The current state of literacy in our advanced civilization:

yo
wassup
nuttin
wan2 hang
k
where
here
k
l8tr
by

- from Usenet (what's *that*?)
 
"David Nebenzahl" <nobody@but.us.chickens> wrote in message
news:4db28ccc$0$10024$822641b3@news.adtechcomputers.com...

My Magic Chef, which I got used, lessee, 23 years ago
or so and still works perfectly, has a very accurate clock.
Crystal-controlled, I'm going to guess.
Click to expand...
In the US, line frequency used to be (and probably still is) "tweaked" so
that clocks with synchronous motors would have zero net error over a long
period of time. This should give better accuracy than a crystal.
 
On 4/23/2011 7:05 AM, William Sommerwerck wrote:
"David Nebenzahl"<nobody@but.us.chickens> wrote in message
news:4db28ccc$0$10024$822641b3@news.adtechcomputers.com...

My Magic Chef, which I got used, lessee, 23 years ago
or so and still works perfectly, has a very accurate clock.
Crystal-controlled, I'm going to guess.

In the US, line frequency used to be (and probably still is) "tweaked" so
that clocks with synchronous motors would have zero net error over a long
period of time. This should give better accuracy than a crystal.


Correct. In fact back in the early 70s when they had the big
Click to expand...
power outage in the NorthEast US my sister was working at a
radio station that checked their electric clock against WWV
every day. When the blackout occurred their clock lost a bunch
of time (I don't remember exactly how much) due to the load
slowing down all of the generators. They reset it and then for
the next week or more they had to set it back every day as the
mains frequency was cranked up a bit until the long term
frequency was returned to 60 Hz. In fact it was for a long
time known that long term stability of the 60 Hz power was
some of the best available. Short term was never as good, it
tended to cycle up and down a bit according to various things
happening.

Bill
 
"John Tserkezis is a Tserk "


Regardless, locking your clock to mains is not always a great idea.
Some areas are just plain wrong. I have a mains locked clock here that
loses a minute every week or so.
Click to expand...

** This fucking, retarded fuckwit has just gotta be totally INSANE !!

The fool has NO IDEA what an energy " supply grid " even is.

Hint - all the alternators are LOCKED IN PHASE all of the time.

No magic - no alternative is even possible for them.





..... Phil
 
On Apr 22, 12:35 pm, jeff_wisnia <jwisniaDumpThisP...@conversent.net>
wrote:
 From my "I can't believe they'd make it this way" list.

Last year I purchased a new Westinghouse Model WST-3501 microwave oven
for our office lunchroom.

It heats and cooks things fine, but has one lousy feature which I can't
avoid noticing and which irks me very time I see it.

The TOD, which is displayed whenever the unit is on standby, loses about
two minutes a day, and has to be reset every few days to keep from
falling ridiculously behind.

I'm shocked, shocked, that the clock isn't synced to the 120 volt 60 Hz
power the unit runs on, like every other line powered appliance with a
digital TOD display I own.

The only reason I can guess for the poor timekeeping is that the
circuitry/board running the clock is used on their 220 volt 50 Hz
versions without modification, so the makers decided not to use line
sync for the clock, and probably didn't want to spring for a crystal
oscillator either, so used an RC one instead.

I tried emailing Westinghouse about this and they fobbed me off to a
subsidiary who couldn't even bother to respond to an email.

Thanks for reading. Anyone got any other ideas about why the stupid
clock in this microwave loses time?

Jeff

--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.8*10e12 furlongs per fortnight.
Click to expand...
Donate it...and buy a new one. I've never had an appliance with a
digital clock that kept poor time. Coffee maker, oven/range, MW, or
VCR.
 
On Fri, 22 Apr 2011 13:35:47 -0400, jeff_wisnia
<jwisniaDumpThisPart@conversent.net> wrote:

From my "I can't believe they'd make it this way" list.

Last year I purchased a new Westinghouse Model WST-3501 microwave oven
for our office lunchroom.

It heats and cooks things fine, but has one lousy feature which I can't
avoid noticing and which irks me very time I see it.

The TOD, which is displayed whenever the unit is on standby, loses about
two minutes a day, and has to be reset every few days to keep from
falling ridiculously behind.

[snip]

Jeff
Click to expand...
I have a small coffee maker that has never kept good time. My guess
is that *any* noise on the AC line affects the pulse counting. I have
a weather station whose clock is synced to NIST, so no longer bother
to set the clock on the coffee maker.

John
 
On Apr 22, 10:27 pm, John Tserkezis
<j...@techniciansyndrome.org.invalid> wrote:
jeff_wisnia wrote:
I'm shocked, shocked, that the clock isn't synced to the 120 volt 60 Hz
power the unit runs on, like every other line powered appliance with a
digital TOD display I own.
The only reason I can guess for the poor timekeeping is that the
circuitry/board running the clock is used on their 220 volt 50 Hz
versions without modification, so the makers decided not to use line
sync for the clock, and probably didn't want to spring for a crystal
oscillator either, so used an RC one instead.

 I don't think this is a 50/60Hz issue.  From the error rate you
describe, it should run faster not slower, and by a larger margin too.

 Regardless, locking your clock to mains is not always a great idea.
Some areas are just plain wrong.  I have a mains locked clock here that
loses a minute every week or so.
 I have cheap non temperature compensated crystal locked clocks that are
by far superior to that.

 The answer is worse than that.

 The clocks are built to a price, the cheapest possible price.

 Consider this: A microwave oven doesn't need a clock at all, just a
timekeeper for timed cooking.  Accuracy is not a priority here at all.
 The fact they have clocks at all means the manufacturers wanted to get
one leg up on the competitors without expending any money.

 We're not talking cameras in cellphones here, there is NO reason for
them to make their clocks accurate, because non of the competition are
going to bother either.
--
To err is human. To moo bovine
Click to expand...
So you live in a place _not_ on the grid?

G˛
 
On Apr 23, 10:02 am, n...@jecarter.us wrote:


I have a small coffee maker that has never kept good time.  My guess
is that *any* noise on the AC line affects the pulse counting.  I have
a weather station whose clock is synced to NIST, so no longer bother
to set the clock on the coffee maker.

John
Click to expand...
So...a surge suppressor might fix it?
 
On Apr 22, 5:29 pm, "William Sommerwerck" <grizzledgee...@comcast.net>
wrote:
Some years back our group designed a micro controller
project that used AC line zero cross for phase triggering.

Did it work by looking for a polarity change, or near-zero voltage? If the
latter, line noise might cause it to miss some zero crossings, and the clock
would run slow.
Click to expand...
It looked for zero crossings directly into the interrrupt input (via a
comparator to clean it up). I had many more problems with extra rather
than missing pulses. That was solved easily by using one of the
processor timers to disable interrupts until almost time for the next
external. I really need to implement the WWVB receiver to REALLY keep
it accurate.

G˛
 
On Sat, 23 Apr 2011 12:08:43 -0700 (PDT), stratus46@yahoo.com wrote:

I really need to implement the WWVB receiver to REALLY keep
it accurate.
Click to expand...
Maybe. In about 2005, I got a consulting gig to clean up a WWVB
receiver design inside a microwave oven. Operation was deemed erratic
by the engineers. I had 1 week to pull off a miracle, and predictably
failed. The product was released with a ceramic resonator.

I'll spare you the details, but methinks it won't work. The basic
problems are:
1. WWVB does not have world wide coverage. You'll need a receiver
that scans from 40 to 100Khz looking for time sync signals. Of
course, every country has their own protocol. Such chips are
available today, but were not when I was dealing with the problem:
<http://www.c-max-time.com/products/showProduct.php?id=1>
2. To get decent field sensitivity, I needed a big fat loopstick like
this:
<http://www.sparkfun.com/products/10060>
<http://www.c-max-time.com/tech/antenna.php>
The problem is that the Q is sufficiently high that it won't cover the
entire 40 to 100KHz range. Lower Q would work, but at reduced
sensitivity. Just finding a place for the loopstick was a challenge
as it had to be outside the metal cabinet. Manufacturing went
ballistic when they saw the loopstick and announced that the hand
labor involved would dramatically raise the price. They were right.
3. Interference from switching supplies and digital rubbish can be
fatal. A 20Khz switcher will have enough harmonics to kill the LF
receiver. I convinced them to turn off the LED display as a token
"energy conservation" measure. However, my switching cell phone
charger would kill the receiver up to a distance of about 10 ft.
4. The controller group wanted a WWVB disciplined oscillator at any
of the standard CPU clock frequencies (i.e. 3.57Mhz). However, none
of the off the shelf chips offered this feature. As a compromise,
they asked for 1 pps, which was also not offered. When I offered to
feed them encoded BCD character data, they threatened to have me fired
for incompetence.
5. Whatever else I forgot...

At this time, I would suspect it can be done with a GPS receiver. High
sensitivity GPS receivers will product accurate time sync even
indoors.
<http://en.wikipedia.org/wiki/High_Sensitivity_GPS>
It may take nearly forever to obtain sync, but for a microwave oven,
that only needs to be done once or twice per day. If location is an
issue, I can extract the time from some various broadcast and cellular
services:
<http://en.wikipedia.org/wiki/Radio_clock>

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
On Fri, 22 Apr 2011 13:35:47 -0400, jeff_wisnia
<jwisniaDumpThisPart@conversent.net> wrote:

Last year I purchased a new Westinghouse Model WST-3501 microwave oven
for our office lunchroom.

The only reason I can guess for the poor timekeeping is that the
circuitry/board running the clock is used on their 220 volt 50 Hz
versions without modification, so the makers decided not to use line
sync for the clock, and probably didn't want to spring for a crystal
oscillator either, so used an RC one instead.
Click to expand...
Did you look to see what they actually used? My guess(tm) would be a
PZT ceramic resonator.
<http://www.tdk.co.jp/tefe02/ef32_fcr.pdf>
These have an initial tolerance of about 0.3% to 0.5%, which is a
rather large:
24 hrs/day * 3600 sec/hr * 0.0005 = 43.2 seconds/day
If you're losing 120 sec/day, then something is wrong with the ceramic
resonator, the associated capacitors, or the CPU. Since you're losing
time (running slow), the clock oscillator frequency is too low, so
it's probably not the capacitor. Find the frequency, identify the
CPU, and install a replacement resonator.
<http://www.tdk.com/crdata.php>


--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
stratus46@yahoo.com (and Phil) wrote:

So you live in a place _not_ on the grid?
Click to expand...
Sigh.

I do live on the grid. I, along with everyone else was promised that
while short term timing errors on the grid are expected, longer term
errors are tweaked and by far less.
I could have lived with this if they actually meant it.

However, in real life, it's STILL not good enough for clocks. Like I
said, I have many non-temperature crystal locked clocks that are by FAR
better.

I have cheap Chinese digital watches (NOT on my wrist) at the whim of
the seasonal temperature environment that have minor seasonal shifts,
but over the year are better than mains-locked clocks.

I can't even get a straight answer googling. Lots of nice graphs that
really don't answer the question too. The BEST was along the lines of
"is very precise" and "it shouldn't vary too far".

In engineering terms, that's just plain bullshit.
--
Include this in your CONFIG.SYS File: BUGS=OFF
 
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