Meinberg Device Configuration Guidelines

Most Meinberg devices used for time synchronization have an internal system clock which usually runs on UTC and is driven by a high quality oscillator.

Time synchronization software such as NTP daemons or the time adjustment service included in the Meinberg driver package for Windows also expect that the time read from the device is UTC, or can properly be converted to UTC. If this is not the case, there is a risk that the computer's system time will be set incorrectly.

Outgoing timing signals (pulses, frequencies, etc.) as well as serial time strings, time codes, and time stamps that can be read via API calls are derived from the disciplined on-board system clock.

Most devices also provide a way to configure an on-board time zone that is exclusively used to convert the on-board UTC time to some local time that is used for the output signals.

In order to ensure that the time in the outgoing signals is always correct according to the on-board time zone settings, it is necessary that the underlying on-board time always corresponds to the correct UTC time.

Since the internal onboard system time is always based on UTC, it is important that the device can always reliably derive UTC from the incoming time signals.

Whether this is possible automatically or whether a special configuration is required depends on the type of input signal.

Time signals from GPS or any other GNSS satellite system contain enough information to unambiguously derive UTC from them.

Therefore, receivers for this type of signal usually do not require any special signal input configuration.

Signals from long wave transmitters such as DCF77, MSF or WWVB have a known UTC offset, so no special signal input configuration is usually required.

An exception can be if an emulated long wave signal is used which has a different local time offset than the original signal.

If the incoming timing signal is an IRIG or similar time code, configuration is often required depending on the particular time code format.

This is because most of the commonly used time code formats neither include a year number, nor some information whether the transported time is UTC, or some local time with an offset to UTC, so the receiver is unable to derive the correct UTC time without further information.

Only the time code formats IEEE 1344 and IEEE C37.118 provide all the information required to let the receiver derive the correct UTC time. IEEE C37.118 is a revised version of IEEE 1344, but processes the UTC offset with the sign reversed, so care mus be taken anyway if some local time is transported by the time code.

More details and some basic information on IRIG and similar time codes is available in the article IRIG Time Code Basics.

Meinberg Time Code Receiver (TCR) devices are usually shipped with the IRIG input explicitly set to unconfigured.

The reason is that otherwise, depending on the time code format transmitted by the on-site generator, there would be a risk that the device could derive an incorrect date or time from an input signal that provides limited information only. Subsequently, a time adjustment service could see that the device was claiming to be synchronized even though the time was incorrectly decoded, and as a result it might set the computer's system time incorrectly.

The reason for this potential risk is not the TCR device, but limitations of some commonly used IRIG code formats like IRIG-B122, which neither contain a year number, nor some information whether the transmitted time is UTC or some local time with an offset to UTC.

If the time code receiver is in the unconfigured state, this risk is avoided and the user can first configure the time code input appropriately.

First find out which IRIG code format is output by the device that generates the time code, and configure the same IRIG code format at the receiver.

For a Meinberg TCR PCI card on Windows, run the GUI monitor program (mbgmon.exe). Click on the IRIG In tab and select the same time code format from the IRIG Code Format selection box.

If the code format is one of the IEEE formats (1344 or C37.118), you are probably done because these formats include a year number and the UTC offset, so no further configuration is required at the receiver side.

Please note that the IEEE 1344 and IEEE C37.118 formats process the UTC offset differently, and there are some 3rd party devices out there that claim to transmit 1344, but in fact transmit C37.118. So if the incoming time code transports local time and not UTC, make sure the decoded time shown on the Radio Clock tab of the monitor program is correct. Otherwise, change the code format from 1344 to C37.118, or vice versa.

If the incoming code format is not one of the IEEE formats, the IRIG time offset to UTC parameter must be set correctly to let the receiver decode the correct UTC time.

You should find out whether the generator transmits UTC or local time with some UTC offset, and enter the appropriate offset accordingly. For example, if the time code provides UTC-2h, you have to enter -02:00 in the IRIG time offset to UTC field.

If the generator outputs local time and the local time steps by 1 hour due to beginning or end of DST, this is not automatically handled by the receiver. Instead, unless manually adjusted, the receiver applies the old offset to the decoded time, which causes the on-board UTC time to follow the step, and as consequence, the computer's system time may also be stepped unexpectedly.

To avoid this, one of the IEEE code formats should be used, or the generator should output UTC, where the offset is constantly 0.

If an IRIG code format is used that does not include a year number (e.g. IRIG-B122), there is a risk that the TCR device synchronizes to the correct time, month, and day-of-month, but within with a wrong year. Consequently, time adjustment programs could set the computer's system time to a wrong date.

To avoid this, one of the IEEE code formats should be used, or an IRIG format that provides a year number (e.g. IRIG-B126), or care must be taken that the on-board date is manually set correctly, e.g. via the Setup→Set Refclock Time menu of the monitor program.

Once it has been verified that the TCR device decodes the correct date and time from the incoming time code signal, the device can be used to adjust the time of connected devices.

With a PCI card or USB device on Windows, the menu Setup→Start time service can be used to start the time adjustment service which runs in the background and keeps the Windows system time synchronized to the time from the TCR device.

The settings of the time adjustment service can be modified via the tabs in the upper part of the GUI monitor program, but the default setting should be most appropriate for normal applications where the computer's system time is to be synchronized.

— Martin Burnicki martin.burnicki@meinberg.de, last updated 2023-02-14