By meansofOption78orOption78/HS,anin-ternal rechargeable battery unit, it is possible to maintain stability during transportation, as the internal reference oscillator is continuously powered.

Field use without access to AC line power is also practicable.

Option 78/HS has the additional feature of ac-ceptinganexternal12VDC supply. Thus it is possible to realize a true uninterruptible power supply (UPS), as the DC source and the AC source can be applied simultaneously. The AC source takes precedence, as long as it is present, and so does the external DC supply over the internal battery, which is kept charged by one of the external sources.

In case of a power line failure you will benefit from double security, if you utilize an external DC source in addition to the AC supply.