Alicat Scientific (Cambridge) are engineering-driven specialists, experts in instrumentation for flowing systems and dead-ended, non-flowing systems—from nitrogen purging or filter characterization, to vessel pressure control or leak testing applications. Alicat instruments are versatile and easy to use because of a rich feature set, yet provide excellent process control through very fast control response (50-100 milliseconds) and high accuracy.
In addition to the standard features that are present across the product lines—like programming easily through a display interface, a serial connection, or an analog connection—a unique differentiator is the company’s dedication to fast-turn-around special projects that benefit the unique requirements of customers across industry. Project solutions should be available within days, not weeks or months, and further complemented by fast delivery times – again measured in days.
Pressure control applications can be enhanced by multivariate, rapid control, as demonstrated with these four examples:
Filter Characterization
As illustrated here, an Alicat Differential Pressure Controller is used to characterize a filter’s flow vs. it’s pressure drop curve. The pressure controller is used to set the pressure drop across the filter through measuring pressure before and after the filter. The mass flow meter is used to measure the flow rate required to generate that pressure drop. Alternatively, the flow meter may be placed upstream of the pressure controller, since mass in equals mass out. Advantages: Serial input of the desired pressure drop allows the user to run canned scripts at known time intervals while a common control interface is used for both pressure and flow.
Manufactured Component Leak Characterization
Many manufacturing process end-tests require a fast, accurate and reliable method for leak checking components. This can be accomplished with an Alicat Scientific mass flow meter, sized appropriately for the expected leak rate, and an Alicat Scientific remote-sensing pressure controller, sized for the required pressure. Alicat Scientific mass flow meters have full scale ranges as small as 0.5 SCCM with 200:1 turndown ratio, meaning that flows as low as 0.0025 sccm (2.5 sulm) can be resolved. If plumbed as shown in the diagram, the pressure is controlled at the entrance to the Device Under Test (DUT). A constant bleed though the needle valve allows the pressure controller to precisely hold the pressure at the DUT, ensuring that any flow through the meter after the bypass valve is closed is due either to leakage or to a cooling of the volume of the DUT. So long as the temperature of the DUT is constant, the flow reported at the meter will be the leak rate of the DUT. Reducing dead volume between the flow meter and the DUT and the volume of the DUT itself will reduce the effects of temperature change and make the leak checking process faster.
High-Efficiency Helium Leak Testing
Alicat’s dual-valve pressure controller is designed to conserve costly gases like helium in closed-volume applications. In this example, the pressure controller first evacuates all the air out of the test chamber. Then it refills the chamber with helium to the desired test pressure. The gas analyzer records any helium that passes through the test device. The integrated exhaust valve of the pressure controller opens only when needed, so it maintains test pressures without continuously outgassing helium through a bleed valve.
Backpressure Control with Flow Monitoring
When there is a need to know the flow rate while controlling pressure, Alicat’s mass flow controllers reduce equipment needs to a single instrument. Instead of using a dedicated pressure controller and a separate mass flow meter, set the mass flow controller to control for absolute pressure. The instrument will now control pressure while simultaneously displaying flow rates. In the accompanying illustration, the mass flow controller allows pressure inside the system to build, simulating the internal pressure of a tire, versus the air compressor that is attempting to fill it.
Conclusions
Specialized application engineering knowledge of measuring and control techniques across a wide spectrum of pressure and flow control processes ensures that the optimum solution can be provided. An optimal solution strengthens an end-users specification and quality, whilst eliminating the costs of wastage and down-time.
Alicat Scientific
2 College Park
Coldhams Lane
Cambridge
United Kingdom
CB1 3HD
E : europe@alicat.com
W : www.alicat.com
T : 01223 472804
