1. Supply Voltage

1.1. Setting

The GPS-12X frequency standard can be con-nected to any AC supply with a voltage rating of 90 to 265 Vrms, 45 to 440 Hz. The frequency standard automatically adjusts itself to the in-put line voltage.


Depending on option chosen, the unit can also be supplied by external DC sources, -48 V or+12 V.

1.2. Fuse

The secondary supply voltages are electroni-cally protected against overload or short cir-cuit. The primary line voltage side is protected by a fuse located on the power supply unit. The fuse rating covers the full voltage range. Con-sequently there is no need for the user to re-place the fuse under any operating conditions, nor is it accessible from the outside.

CAUTION: If this fuse is blown, it is likely that the power supply is badly damaged. do not replace the fuse. Send the frequency standard to the local Pendulum Service Cen-ter.

1.3. Grounding

Grounding faults in the line voltage supply will make any instrument con-nected to it dangerous. Before con-necting any unit to the power line, you must make sure that the protective ground functions correctly. Only then can a unit be connected to the power line and only by using a three-wire line cord. No other method of grounding is per-mitted. Extension cords must always have a protective ground conductor.

WARNING: If a unit is moved from a cold to a warm environment, con-densation may cause a shock hazard. Ensure, therefore, that the grounding requirements are strictly met.

WARNING: Never interrupt the grounding cord. Any interruption of the protective ground connec-tion inside or outside the instrument or disconnection of the protective ground terminal is likely to make the instrument dangerous.

2. Power Switch

This instrument is equipped with a secondary power switch. It disconnects the main power-consuming circuits on the secondary side of the power supply but leaves the rubid-ium oscillator active in order to retain its long-term characteristics. Line voltage is al-ways present on the primary side.

WARNING: Always consider the instrument active as soon as it is connected to the primary AC power source with a power cord.

3. Orientation and Cooling

The frequency standard can be operated in any position desired. Make sure the air flow through the ventilation slots are not obstructed. Leave 50 mm (2 in) of space around the instrument.

CAUTION: Never cover the ventilation slots at the right or left side. If the slots are covered, the fre-quency standard will overheat.

3.1. Fan Control

The speed-controlled fan is used for adjusting the temperature inside the frequency standard to compensate for variations in ambient tem-perature.

Fig 2-1. Air flow through the GPS-12X.

4. Fold-down Support

For bench-top use, a fold-down support is available for use underneath the frequency standard. This support can also be used as a handle to carry the instrument.

Fig. 2-2. Fold-down support for comfort-able bench-top use.

5. Rackmount Adapter

Fig. 2-3. Dimensions for rackmounting hardware.

If you have ordered a 19 inch rack mount kit for your instrument, it has to be assembled after de-livery of the instrument. The rack mount kit consists of the following:

2 brackets, (short, left; long, right)
4screws, M5x8
4screws, M6x8

WARNING: When you remove the cover you will expose live parts and accessible terminals which can cause death.

WARNING: Capacitors inside the instrument can hold their charge even if the instrument has been separated from all voltage sources.

Fig. 2-6. Fitting the rackmount brackets on the counter.

5.1. Assembling the Rackmount Kit

  • Make sure the power cord is disconnected from the instrument.
  • Turn the instrument upside down.
  • See Figure 2-4.
  • Undo the two screws (A) and remove them from the cover.
  • Remove the rear feet by undoing the two screws (B).
  • Remove the four decorative plugs (C) that cover the screw holes on the right and left side of the front panel.
  • Grip the front panel and gently push at the rear.
  • Pull the instrument out of the cover.