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General Issues > Time Stamps

Crystal-based timing

Let´s first discuss the level of precision that can be expected from crystal-controlled timers. Typical computer clock oscillators, although quarz-controlled, are generally insufficient because their low-cost components have a typical frequency error in the order of ±100 ppm. This translates into an uncertainty factor of 1 hour per year.

There are higher quality crystal oscillator modules on the market called precision oscillators (PXO). Their error is normally less than ±10 ppm across a full temperature range. But this is still an inacceptable figure.

Another commercially available timing device is the temperture compensated crystal oscillator (TCXO). Now, we can expect a precision of typically ±1 ppm across a full temperature range—and a significantly increased cost per unit. Still, we would end up with an accumulated error of ±100 ms after 24 hours of stand-alone operation. Again, this is not an appropriate solution for the RED System‘s Network.

We could have an even higher level of timing precision (based on crystal oscillators) if we were to employ a state-of-the-art oven-controlled crystal oscillator (OCXO). Here, the crystal is held at a constant temperature of typically 60 °C. These units are specified to deliver a timing precision of better than ±0.1 ppm—at relatively high cost.

Yet there is still a problem: the oven typically consumes more than 100 mW of power, meaning that the commitment to low-power operation would have to be given up. No, this cannot be the solution for the RED System.