Pinch valves are keystone to sample management as pinch valves hold and deliver the sample from stage to stage. Off the shelf pinch valves are limited to 2 bar, but we successfully modified the pinch valve design to 7 bar. The modification maintains the diameter of the silicone hose replacing it with more robust flexible plastic hose with an inner silicon hose while increasing the spring tension to in- crease the pinching force. The pinch valve was over driven with 24v, increasing the pinch force for 200ms, thereafter, the pinch valve kept the plastic hose closed with a minimum force.
We begin by describing the pinch valve circuit (fig 1) components: 1) An ultra high precision, ultra low noise, series voltage reference, 2) Exercise valve 3) An active low pass filter, 4) A MOSFET current sink and Op Amp with negative feedback, 5) Over drive, 6) Valve feedback, and 7) Temperature sensor. In addition, we employ various Matlab toolboxes to develop the small signal model for the active low pass filter and current sink, and consequent simulations result in the complete input/output TF (Io/Vin ) shown in equation (1), zeros and poles are listed in table (1).