R.6 Time Synchronization
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## R.6 Time Synchronization

Medical device time requirements primarily deal with synchronization of machines on a local network or campus. There are very few requirements for accurate time (synchronized with an international reference clock). DICOM time users are usually concerned with:

1. local time synchronization between machines

2. local time base stability. This means controlling the discontinuities in the local time and its first derivative. There is also an upper bound on time base stability errors that results from the synchronization error limits.

3. international time synchronization with the UTC master clocks

Other master clocks and time references (e.g., sidereal time) are not relevant to medical users.

### R.6.1 High Accuracy Time Synchronization

High accuracy time synchronization is needed for devices like cardiology equipment. The measurements taken on various different machines are recorded with synchronization modules specifying the precise time base for measurements such as waveforms and multi-frame images. These are later used to synchronize data for analysis and display.

Typical requirements are:

Local synchronization

Synchronized to within approximately 10 millisecond. This corresponds to a few percent of a typical heartbeat. Under some circumstances, the requirements may be stricter than this.

Time base stability

During the measurement period there should be no discontinuities greater than a few milliseconds. The time base rate should be within 0.01% of standard time rate.

International Time Synchronization

There are no special extra requirements. Note however that time base stability conflicts with time synchronization when UTC time jumps (e.g., leap seconds).

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