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Forums > CSDb Discussions > 1541 Quartz speed on real device.
2020-08-22 23:40
Flavioweb

Registered: Nov 2011
Posts: 413
1541 Quartz speed on real device.

With the help of Ready. we measured the quartz frequency of a 1541 directly on the motherboard, with the drive running, to make a precise test by evaluating the values in a condition of real operation.

This is the quartz mounted on the drive we have tested:

The test lasted about 2h and 30 mins, during which the electronics were covered to simulate the presence of the top of the chassis.
The maximum temperature reached by the quartz was about 45c if covered and about 39 if uncovered.

For the whole duration of the test a frequency value oscillating between 16.000 and 16.0001 mhz was detected. No values higher or lower than these.

In the quartz tech specs we found a maximum drift of +/- 50ppm, which means:
50 * 16 = 800 = 16.000.800 / 15.999.200hz in the worst case.

During our test, instead, we found, in the worst case, a drift of 100hz, therefore 1/8 of the theoretical one found in specs, ie 50/8 = 6.25ppm.

Making a few calculations just to relate ppm to rpm, we have:
6.25 / 5 = 1.25 (ppm / (1mhz / hz per revolution)) = drift per revolution
1.25 / 200,000 = 0.00000625
300 * 0.00000625 = 0.001875 rpm calculation error due to the quartz drift in the worst case.

We do not know exactly, during the whole period of normal operation of the drive, what is the precise value of ppm of deviation, but we know with certainty that it is a number between 16,000,000 and 16,000,100 hertz, so 100/16 = 6.25ppm in the worst case.
 
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2020-08-25 19:45
Groepaz

Registered: Dec 2001
Posts: 9532
Just don't make the mistake of misinterpreting those two measurements into the general case - generally we still have to assume what the datasheet is true, more or less. Because if the manufacturer would have been able to guarantee ~6ppm deviation, you can be very sure he would have not written 50ppm into the datasheet :) Right now those measurements can be taken as anecdotal - no more no less.
2020-08-27 13:17
Zibri

Registered: May 2020
Posts: 129
Quoting Groepaz
Just don't make the mistake of misinterpreting those two measurements into the general case - generally we still have to assume what the datasheet is true, more or less. Because if the manufacturer would have been able to guarantee ~6ppm deviation, you can be very sure he would have not written 50ppm into the datasheet :) Right now those measurements can be taken as anecdotal - no more no less.

Wrong:
the manufacturer can't guarantee weather conditions or ambient temperatures.
The ppm is hence calculated, so probably at the north pole in the cold it will go slower than in the middle of the deser at 1 pm.
But in most cases the quarts will be in a 18-38 degrees environment.
Also it may happen that some "unlucky" quartz are bad but still within the 50ppm "specs" so they will be safe from legal actions about mislabeling.
2020-08-27 13:23
Groepaz

Registered: Dec 2001
Posts: 9532
All you can actually rely on are the specs in the datasheet, under the conditions listed in the datasheet. Not doing so is amateurish tinkering. There are no "unlucky" components, there are only components that operate within the specs, and components that do not.

And no, not wrong. If they could guarantee certain things within certain more narrow conditions - they'd write it in the datasheet.
2020-08-27 13:24
ChristopherJam

Registered: Aug 2004
Posts: 1078
Quoting Zibri
the manufacturer can't guarantee weather conditions or ambient temperatures.


Of course not. But what they do do, is specify a range of ambient conditions under which they will guarantee the clock speed is within a given tolerance.
2020-08-27 16:22
Oswald

Registered: Apr 2002
Posts: 4607
the error of the measuring device should be also accounted for.
2020-08-27 17:01
Groepaz

Registered: Dec 2001
Posts: 9532
which is why it's listed already, indeed.
2020-08-27 17:13
Zibri

Registered: May 2020
Posts: 129
Yes. I realize this and both Oswald and Christopher are right.

What I am saying is that is totally irrelevant to the RPM speed test which express the speed in cents of rpm...
The "differences" in quartz do not influence the results if nor very marginally.
2020-08-27 17:46
Groepaz

Registered: Dec 2001
Posts: 9532
This thread is about the crystal speed though, not about RPM testing.
2020-08-30 05:29
Zibri

Registered: May 2020
Posts: 129
Quoting Groepaz
This thread is about the crystal speed though, not about RPM testing.

Right, but the crystal speed was tested because "someone" implied that my RPM test was anyway inaccurate because of the crystal. Which was so proven not to be relevant in the calculation.
2020-08-30 12:48
Groepaz

Registered: Dec 2001
Posts: 9532
everyone understood that by now, and its irrelevant for this discussion.
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