|High-resolution digital frequency counting
Frequency calibration to relative accuracies of better than 1 part in 108 has traditionally required complicated setups, or have been time-consuming to perform, with frequency counters that needed long measuring times to achieve the required resolution.
With a virtual clock frequency of 4 GHz, Fluke"s PM 6685R offers an unmatched resolution of 2.5 x 10-10 per second, giving 10 reliable read-out digits in only one or a few seconds. This makes high-accuracy calibration measurements possible, with the convenience of requiring only a digital counter.
The wide choice of input options allows digital calibration measurements at up to 8 GHz, without the complexity of needing to use synthesizers, mixers and filters to provide the required resolution down to the last digits.
Additionally, digital counting techniques allow a numerical offset or nulling of the display value to make it easy to read changing or arbitrary frequency values with many different digits.
Guaranteed high stability for field operation
The built-in Rubidium reference solves the practical problems of ensuring very high stability under severe field conditions.
The atomic resonance principle of rubidium standards is intrinsically 100 times more stable than an electromechanical crystal resonator; a fact that contributes to making the PM 6685R the most accurate counter/calibrator available for field use.
Also, the atomic reference does not suffer from mechanical, thermal, vibrational and line voltage influences in the way that a crystal oscillator would. When carrying a crystal-based counter, for example, just one small bump against a step can cause more frequency change than several months of aging under controlled calibration laboratory conditions.
This stronger resistance to environmental stress on the reference permits longer calibration intervals in many practical situations, making the PM 6685R more convenient for field personnel and reducing the cost of ownership. In fact, using the PM 6685R at a field site may even reduce the need to send other elements of a field lab out for their own respective calibration.
Rubidium references should therefore be considered for all meaurements or calibrations in the field where accuracies better than a few parts in 108 are required, or where frequent calibration of the counter is not possible.