Model BetaCAP60-3G - Double Gas Diluter
BetaCAP60-3G is a 60-step diluter, capable of diluting 2 gases in a diluting gas, in any relationship between them. BetaCAP60-3G was created to satisfy the need of combining linearity tests with the possibility of performing interference tests. For this purpose, having two components (measuring and interfering) pure or contained in mixture in different cylinders, these can be diluted differently and independently. To clarify the operating conditions, it is convenient to define the three gases as diluted gas, interfering gas and diluting gas : each of the three gases, can vary virtually between 0 and 100% (60:60) of the applied concentration. In reality, the possible variations obviously depend on the presence of the other two gases, and in particular, on the condition “gas to be diluted + interfering gas + diluting gas = 100% (or 60:60).
The menu page shown here (menu translation in progress) shows the dilutions area : the dark square inside the triangle indicates : gas to be diluted = 36:60, interfering gas 12:60 and consequently, diluting gas (60-36-12) = 12 : 60. Keeping constant the dilution of the gas to be diluted, it is possible to vary that of the interfering gas by moving the square vertically, and vice versa, to modify the dilution of the measured gas by moving it horizontally.
The sides of the triangle correspond to dilutions with only two gases, while the entire internal area corresponds to different combinations with the presence of all three gases.
The 60 capillaries used in BetaCAP60-3G are selected in order to have extremely uniform characteristics : this feature is transferred to the product, which is characterized by an excellent initial accuracy
Three pressure regulators (inlet-outlet) are electronically regulated with repeatability <1 hPa (out of 3,000). All dilution combinations produce a constant diluted flow : the total flow is always 60 x single capillary flow.
When this unit is used for linearity tests, the major division is 1:60 : this means that for a test in 5 steps it is possible to use a test gas concentration up to 12 times the analyzer’s measuring range : this reduces considerably the size of the cylinder park and the related costs
BetaCAP60-3G is however particularly useful when the user needs to verify and measure the interference on the measurement of a component by a different component: this is the primary purpose of the product, which distinguishes it from the CAP30 range.
Functional disgram of BetaCAP60-3G
In the above diagram we can identify two functional areas: an upper one with the capillaries and the solenoid valves that select the gas arrival and a lower one that manages the three entry ways and the related pressure adjustments.
a) in the upper area, each of the two modules with 30 capillaries (1 + 2 + 4 + 8 + 15) is practically identical to a BetaCAP30 and work the same way
b) in the lower area of the drawing, the two solenoid valves EV11 and EV12 direct the three inputs TG1, TG2, TG0 towards the two dilution modules according to which dilutions are to be made. The state represented in the diagram is valid when Kdil.10.5 (EV11 and EV12 are activated) or Kdil.2> 0.5 (only EV11 is activated) one of the two dilutions is realized with the concurrence of both modules. The three regulation valves VR1, VR2, VR0 maintain the differential pressures at the ends of the capillaries at the calculated value (P1, P2, P0).
By using in the electronic circuits advanced micro-controllers, we could place in theyr program a discrete amount of calculations, obtained by applying the physics laws that describe the laminar motion of fluids in the capillary ducts. When the viscosities of the three gases are similar, they do not need many calculations : the dilution is a digital matter (Capillaries ON if crossed by the gas to be diluted or capillaries OFF if crossed by the diluting gas). When, on the other hand, the viscosities of the three gases are substantially different or the User wants to obtain dilutions different from the 60 points immediately available, at the dilution it must be applied analogical threatments , such as the regulation of P1, P2, P0 on different and calculated setpoints. Including the viscosities of the given mixtures, everything is calculated without troubling the User or even giving him the perception of how complex the work is.
The color graphic display with touch screen receives the inputs from the User and informs him about the status of the diluter (regular parameters or alarms).
A noteworthy function (but probable subject of discussion) is the “self-referring calibration” explained in a document at the link Cal.AutoRef., It uses an optional flow measuring module to perform a progressive series of comparisons between theoretically equal flows, finally obtaining the deviations between the measured and the ideal flows . In accredited environments, I believe that nobody will use this function for the calibration of the diluter, while it will be a valid support for decisions regarding the expiry time of the metrological certificate.