BetaCAP60-3G did born to satisfy the requirement of testing both linearity and cross sensitivity to interfering compo-nents. The three differential pressures referred to the output are electronically regulated in order to have the pressures balanced for all the capillaries regardless of whether they are crossed by TG0, TG1 or TG2,
While for the linearity tests are used only two inputs, and 60 steps are available, for testing the interference all three inputs are required (gas to be measured, interfering gas, diluent gas): normally it's fixed a dilution ratio for the gas to be measured and the ratio varies for the interfering gas, increasing its concentration until the interfering effects are visible on the measured concentration of the interfered component. Each of the three gas, may affect a capillary number ranging from zero to 60. If the gas to be measured affects 6 capillaries, and interfering gas affects 30 capillaries, the diluent gas automatically affects the remaining 60-6-30 = 24 capillaries. Gas measured and interfering gas will be diluted in this case by a factor 0.1 (6:60) and 0.5 (30:60)
One of the operating menus shows the possible dilutions: The small red squared in bottom left corner of triangle represents a situation in which TG1 (measured) affects 0 capillaries, TG2 (interfering) affects 0 capillaries and TG0 (diluting) the rest (60-0-0)=60,
Moving the red point vertically, the measured
concentration stays constant and the interfering concentration do change and
moving it horizontally just changes the measuning gas dilution.
The sides of the triangle (green colour) corre-spond to dilutions with only two gases, while the whole inner area corresponds to the different combinations with three gas
The operator is asked to input the concentration of measured gas in the test gas bottle and the concentration of interfering gas in the second gas bottle. The viscosity of the three mixtures or gases is automatically calculated from the given test gases composition.to allow the automatic compensation of viscosities, got by unbalancing relatively the three differential pressures (inlet-outlet) set point. In the operating menu, the user may choice both for measured and interfering gas the dilution factors, reading the consequent theoretical diluted concentrations.
Despite the high relative accuracy of the capillaries (compared one each other), we did setup an errors calculation procedure (automated by PC) for the final product (where single capillaries may not more be accessed) in which the measurement of diluted concentration or the output flow measurements are acquired by the PC and processed. :
- one of the 60 capillaries is assumed as "reference" (error = 0)
- a series of comparisons between nearly equal measurements (the linearity of the external meter is not critical) is done involving one at a time in a growing sequence all the capillaries groups and determining the error for each group.
All the calculated errors are referred to the first "reference" capillary. The PC program "Errors evaluation" is given free with the BetaCAP60-3G unit. Knowing the errors, the user may decide if to compensate them with a diluter special function or not to activate this compensation.
The PC program InfoCAP3000 is very near to be released to allow fully automatic testing. The Diluter is equiped with a serial line RS485 with the same AK protocol used by the other units. When needed, users may built their own software to get automatic runs of the interference tests : an impostant feature is the availability of four acquired analog signals (the analyzer measuring signals) that may be tranferred to PC by one of the AK commands. At request we may send to our clients detailed information about our functions with AK.
As with other units of the series BetaCAP, even BetaCAP60-3G may be operated with the "continuous dilution" mode : that means an available uninterrupted dilution range from 0,833% to 99,166%; zero and span are also available.
It's possible to include the option for fixed ratio 100:1 pre-diluting one of the three inputs, which may allow getting up to 83.33 ppm from a pure gas ! When not required it's bypassed.