The Auto-Needle Valve system is used to control and regulate gas pressure via Labview software. Pressure is controlled via a PID control loop which determines the needle valve position. Typial error band on systems is ±0.2mBar which means that the needle valve does not react to fluctuations between +/- 0.2mBar. These values may be changed by the user as required.
The example below used an Inficon VGC501 pressure controller reading a Capacitance/Pirani combo gauge. ICEoxford's labview based software reads the pressure information and controls the needle valve position accordingly through a 0-10V signal to the valve controller.
The graph shows that the needle valve position changes quite significantly during pressure controls. This is due to the variation in helium gas temperature (and therefore density) that systems experience. It is clear that we can control pressure very accurately only using a needle valve.