Flow Sensor Calibration
The hydrogen and oxidant flow sensors installed in the Dual Plasma Controller have very good repeatability, but significant non-linearity. They have each been factory calibrated at the midrange flow rate (50 SCCM) using an NIST traceable flow meter. Over the typical operating range for the SCD, the flow sensors should produce accuracy of better than ±10% of reading. However, due to sensor non-linearity at low or high flow extremes, error greater than this could be observed.
If greater accuracy is desired at a particular flow rate range, it is possible to re-calibrate the flow sensors. A reference flow meter, appropriate gases, and a trim-pot adjustment tool are required for this procedure. With the controller on and no gases flowing, the zero calibration points are set with RP6 and RP4 for the hydrogen and oxidant flow streams, respectively. Connect a reference flow meter to the gas outlet(s) on the back of the controller. Connect pressurized gas line(s) to the inlets on the back of the controller. Connect jumper (JP1) to bypass the pressure fault circuitry. Allow the burner temperature to exceed 325 °C in order for the hydrogen and oxidant valves to be open. The spans of the sensors are then adjusted for the particular flow stream to the desired flow rate as measured with the reference flow meter. The span adjustments are set with RP3 and RP2, for hydrogen and oxidant respectively, so that the display on the controller matches the value obtained with the reference flow meter. Upon completion, remove the reference flow meter and return the bypass jumper (JP1) to its original position.
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