Patent ID: 8887549

Claim:
A method for determining leakby in a flow controller installed in a process equipment using a first valve directly attached to an inlet side of the flow controller and a second valve directly attached to an outlet side of the flow controller, the method performed while the flow controller remains connected to the process equipment, wherein the flow controller includes a thermal mass flow sensor, internal electronics, and a flow control valve that are all integrated within the flow controller, the method executed by the internal electronics inside the flow controller, the method comprising: stopping flow through the flow controller by closing the first valve and the second valve; determining a flow rate using a thermal mass flow sensor; comparing the flow rate with a previously stored flow rate to determine a zero drift (Qdrift) value for the thermal mass flow sensor; resuming flow through the flow controller by opening the first valve and the second valve; determining, using the thermal mass flow sensor, a second flow rate (Qflow) through the flow controller when the flow controller is in a fully closed position; and determining the leakby through the flow controller where the leakby is equal to Qflow-Qdrift.