Customer Tuneable PID Control. Alicat MFC’s are factory tuned to give “average” flow responses to set-point change to enable them to function well across a whole range of diverse applications. In addition, factory pre-set tuning is available when a customers’ specific conditions are known, however, more important still is the ability for the customer to tune in situ when conditions were unknown or when they change. This in-process tuning allows the speed of response to be further increased over and above the general responses mentioned below.
30 – 100 ms Fast Control Response. Not only is the measurement of flow extremely fast but so are the control electronics and control valve are also fast to give typical flow rate response times of between 30 and 100 milliseconds.
Bi-Directional Mass Flow Control. Bi-directional mass flow controllers have two valves; one to control the flow in a forward direction, the second to control the flow in the backwards flow direction. The first valve is connected to a pressure source to provide the motive force to generate flow; the second valve can be connected to a vacuum source to then “pull” the flow through in the opposite direction.
Stand-alone Control Functionality Especially with the Integrated Potentiometer Option. By having the factory pre-set, or by selecting the local set-point option via the front screen buttons, it is possible to operate the device in stand-alone mode whereby the set-point can be increased or decreased at the push of a button. Other than the power cord, no other cables or electrical signals are required. This can be made even easier by selecting the integrated potentiometer fitted to the top of the electronics housing whereby the set-point can be varied by simply turning the pot.
Ramp Function. The ramp rate can be set serially or via the front panel and can be applied to the control of mass flow, volumetric flow or the pressure. The rate of ramp rangers from instant through to one week to get to full scale (at 0.1% rate resolution) all the way to three months to full scale (with 1% rate resolution). The ramp can be selectively applied to UP, DOWN or both with selectable response on zero setpoint to either ramp or instant off.
Valve Hold Function. A valve “hold” function can be applied that sets a constant control signal to the valve thereby holding it in the same position regardless of process change. This is useful for such situations as when the pressure needs to be changed and there is the risk of PID conflict within the flow path. The user can 1. set hold on the mass flow controller, 2. Adjust the process pressure via the Alicat pressure controller, 3. Turn off the hold function and resume normal variable control of the flow rate.
There are numerous other benefits to an Alicat Mass Flow Controller including the following. Multiple alarms, separate from control, voltage source or open drain. No straight run of pipes are required. Alicat devices can control to the lowest set-point on the market, 0.0025 sccm. Alicat devices are tough and survive bumps, dings and even being dropped.
