[ntp:questions] Trying to use Dimension 4 time keeper

David Taylor david-taylor at blueyonder.co.uk.invalid
Wed Sep 11 05:19:30 UTC 2013

On 11/09/2013 02:47, W. eWatson wrote:
> ...
>>>>> I tried Meinberg for quite some time, but it flops fairly often. As I
>>>> flops? What are the symptoms? Also, if time is important why not invest
>>>> in a GPS (35 dolalrs or so) with PPS.
>>> It moves many seconds in a short time, say a day or two. How is GPS
>>> going to help? Does it provide access via a USB port.
>> It-- which noun does that "it" point to?
>> Sure, you can have gps provide access via a usb port. The Sure GPS even
>> has a usb port on board that you can directly connect to. It is not
>> great timekeeping but you can probably get it to within .1 sec or so.
>> The main problem is that you cannot use the PPS via a usb connection, so
>> you have to rely on the timing from the nmea sentences. Run the usb port
>> as fast as possible (high baud rate), and after some observation with
>> the machine connected to the internet as well, determine what the usb
>> data time offset is and subtract it out using the time2 option to the
>> driver.
> It = GPS. What is PPS?
> ...

PPS = pulse per second, required for the most accurate time keeping. 
Typically, the RS-232 DCD line is pulsed high for 100-200 ms at the 
leasing edge of the UTC second.  Requires a GPS (or other) receiver 
capable of delivering PPS, such as those listed here:


Contrary to what you were told, with the right USB adapter you /can/ use 
PPS over USB, although the results will not be as good as using PPS 
directly to a COM port, but they can be better than relying on Internet 
alone, or serial GPS (direct or over USB) alone.

Web: http://www.satsignal.eu

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