Electronic – How to calculate the frequency accuracy of a Fluke DMM

In Australia, the interconnected grid frequency is held to a nominal frequency of 50 Hz, to be within ± 0.15 Hz 99% of the time. The accumulated time error may not be more than five seconds.

Excerpt from the AEMO Frequency Report Reference Guide:

The various Australian power utilities do a pretty good job of maintaining the target frequency and accumulated time error within the stated limits. AEMO publishes reports on this monthly - for the month of June 2013 the accumulated time error in Queensland varied between + 2.40 and -3.77 seconds.

From this, we can conclude that the 50 Hz power system frequency is an OK clock signal - but only so long as your time-keeping device has uninterrupted access to the power grid!

Here is a list of conditions that may cause you to lose your mains power, and therefore your time reference:

• Someone turns off the mains power switch to your device
• A circuit breaker trips in your house
• The power goes out on your street
• A transient fault occurs on the distribution network - enough to result in a brief 200ms auto-reclosing cycle
• A major fault occurs on the transmission network - the grid goes black in your area

You would almost certainly be better off finding some other way to keep time. A GPS time receiver (ref. "IRIG B") is common in applications where precise time keeping is required, such as power systems protection relaying.

There's no "Industry Standard". Each Protocol specifies an allowable frequency error. For example, according to this R&S document https://www.rohde-schwarz.co.jp/events/webinar/lte_ue_rf_measurements_v122.pdf

LTE requires 0.1PPM transmit accuracy, referenced to the received frequency. It's achieved by using a TCXO in a control loop, with the received frequency used as a reference, so it does work with the base station to control the frequency.

The Feature phone at $20 or $30 actually costs more than that, handsets in the US are subsidized by the carriers, so what you pay is a fraction of what the carrier paid.