SCADAPack Transmitters

When using US measurement units, and the differential pressure on a 4202GFC or 4102MMT is calibrated using the RealFLO Calibration wizard, the "As Found" and "As Left" values recorded in the event log do not appear to match the calibration values used during the calibration. This is true for RealFLO versions up to and including RealFLO 5.24.

Description

The issue shows up when the flow run measurement units are set to US2, US4, US5, US6, US7 or US8. Under these circumstances, calibration is performed using differential pressure engineering units in inches of water column at 68 degrees F (20 C), however, the records in the event log due to the calibration are recorded in inches of water column at 60 degrees F. It is this difference in engineering units that results in calibration as found and as left records that appear to be slightly different from what is expected. (You may wish to note that a given differential pressure when measured with a water column at 68 degrees, will result in a slightly higher water column when compared to the same measurement, using a water column at 60 degrees due to the lower density of the water at the higher temperature).
The 4102 MMT and 4202 GFC sensors do not presently support a differential pressure unit set in inches of water at 60F. Therefore, when these sensors are calibrated, the Calibration wizard in RealFLO, displays the actual available sensor units (H2O at 68F). This ensures the sensor is calibrated in the same units it is configured for. During the calibration, the calibrator should be set up for this same units set (H2O at 68F/20C)
When the 'as left' and 'as found' values are recorded in the event log however, the entries and readings are actually converted to the flow computer run units (H2O at 60F when using US2).

The result will be that the recorded values such as 'as left' and 'as found' values will not appear to be exactly the same as those entered during calibration due to the difference in the unit sets.

Work Around

The differential pressure values recorded in the Event Log using H20 at 60F, when multiplied by 1.00078, will equal the calibration values at H20 at 68F. Or to put it the other way, a reading of 100 inches of water (at 68F) during calibration will actually be recorded in the event log as 99.922 inches of water (at 60F).
The best procedure as it is now if calibration is required, is to perform the calibration with the calibrator set up to work in inches of water column at 68F/20C and be aware that the corresponding values shown in the event log are actually in the US2 run units that are inches of water column at 60F. If you are verifying the readings recorded by looking at the event log, multiply the numbers in the event log by 1.00078 in order to see what was indicated on the calibrator and the calibration dialog during calibration.

Issue Resolution

This situation will be corrected in the next major release of RealFLO so that calibration is always done in the same units as the run units so there is no need for units conversion.