Power & Environment

October 2003

Batteries and inverter on left, HVAC center, humidifier on right.

HVAC system on left, humidifier on right.

Chilled water tank on bottom, air handler center, resistance re-heat top

UPS system, four 8D batteries on bottom, inverter on top.

Trace SW-5548 5500 watt inverter and charger.

Breaker panels and isolation transformers.

Located adjacent to the lab is a small room that contains the HVAC systems and power conditioning equipment.

Atomic clocks are the most accurate and stable devices ever made. However their stabilities can be affected by changes in their enviroment. A 1°C change in room temperature represents a temperature change of 0.33%, or 3.3 parts per thousand. Since the clocks are reaching stabilities of one part in 1,000,000,000,000,000 what would be a small temperature change to us looks huge to the clock. Much effort is expended in the design of these atomic standards to minimize their sensitivities to enviromental changes. For example in the Sigma-Tau MHM-2010 Hydrogen Maser a 1°C change in temperature can cause a change in its frequency that approaches its specified limits. Therefor it is important that the ambient temperature be held as stable as possible. The goal in the clock vault is to maintain the temperature to a change of less than +/- 0.15°C

The requirement for stable and reliable power is also critical. A loss of power at the clock means a loss of the "TIME" (The equivalent of a total melt down.)

The first step in assuring a robust power supply is a good stand-by generator. A 35 killowatt diesel generator backs-up the entire home and lab. Because there is a time lag between power loss and the generator coming on line an Uninterruptible Power Supply (UPS) is needed. A Trace SW5548 inverter/charger fills this need. It is capable of supplying over 5 killowatts of power. With four 8D batteries the UPS can supply continuous power for several hours. The UPS can withstand most power outages however at this rural location outages of 4 to 8 hours are not uncommon.

The mains power is further conditioned by two 5 KVA isolation transformers. In addition two “Staco” 6 kilowatt Automatic Voltage Regulators have been purchased and are scheduled to go on-line soon.

In addition to the generator and UPS each clock has dedicated batteries in or near the clock. These batteries are capable of running the clock for several hours. For example each Agilent 5071A cesium clock has an internal battery capable of running the clock for 45 minutes plus an Austron 1290A standby battery pack that can run the clock for over 10 hours. In total there are enough batteries to run all the clocks for over 12 hours.