Revision Date: 08 November 2024
Author: M. Daniels
This article is applicable to the 8270A and the 8370A.
The 6270A is a modular pressure calibrator + controller which can contain up to five Pressure Measurement Modules (“PMM”) to measure the applied pressure covering a wide range of pressure. The PMMs provide the reference level measurement for the 6270A. The PMMs are available in different ranges of pressure from vacuum up to 20 MPa, and there are three measurement performance classes of PMMs to provide different levels of measurement uncertainty.
The PMM selection is based on two criteria. The first criteria is based on the PMM which provides the lowest measurement uncertainty. If there are two or more PMMs which provide the same measurement uncertainty then the second selection criteria is slot number assignment. The PMM located in the lower slot number is selected over a higher slot number.
There is not a requirement for the PMMs to be installed in a particular order when used with a 6270A. The selection of the PMM based upon measurement uncertainty is valid independent of the slot position. The traceability can be attained by querying the 6270A for the active PMM identification. For convenience, it can be desirable to place the PMMs in order from left to right (slot #1 to #5) by ascending order of pressure range. This will also have the benefit of consistency with the 8370A where there is a mechanical requirement to place the highest ranged PMM in the far-right slot (next to the Pressure Control Module).
In the early days of the 6270A life cycle there was messaging from Fluke to place the highest ranged PMM In slot #1 and the lowest in slot #5. This was driven by an unrelated issue with our PC-based software, which has since been fixed.
The PMM selection is based on two criteria. The first criteria is based on the PMM which provides the lowest measurement uncertainty. If there are two or more PMMs which provide the same measurement uncertainty then the second selection criteria is slot number assignment. The PMM located in the lower slot number is selected over a higher slot number.
There is not a requirement for the PMMs to be installed in a particular order when used with a 6270A. The selection of the PMM based upon measurement uncertainty is valid independent of the slot position. The traceability can be attained by querying the 6270A for the active PMM identification. For convenience, it can be desirable to place the PMMs in order from left to right (slot #1 to #5) by ascending order of pressure range. This will also have the benefit of consistency with the 8370A where there is a mechanical requirement to place the highest ranged PMM in the far-right slot (next to the Pressure Control Module).
In the early days of the 6270A life cycle there was messaging from Fluke to place the highest ranged PMM In slot #1 and the lowest in slot #5. This was driven by an unrelated issue with our PC-based software, which has since been fixed.
To fully enable the meaningful module selection by the 6270A it is important to maintain the programmed uncertainty values for the PMMs. These values are password protected and should be validated at the time of calibration of each PMM. The responsibility for assigning the uncertainty belongs to you, the owner of the hardware. As a manufacturer, Fluke provides an estimated uncertainty based on a population sample. These values are provided in the document, “6270A Pressure Controller/Calibrator, Product Specifications”. See table 3 for the PM600 Module Measurement Specifications:
The Zero Stability parameter represents the estimated amount of zero drift unique to each PMM. The values in table 3 are published with the presumption of regular application of AutoZero and therefore do not include the Zero Stability parameter. However, in practice the default for the 6270A is to include this additional source of uncertainty. The magnitude of the zero drift can be reduced by regular use of the 6270A’s AutoZero feature. If the AutoZero feature is not used then the (default) estimated Zero Stability uncertainty is ±0.007% FS of each PMM.