Siemens SITRANS F C MASSFLO, Operating Instruction, Page: 21 / 36

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SFIDK.PS.028.S2.02
Inaccurate mass flow reading
1. Make sure that the SENSORPROM unit has been properly installed in the sensor. If not, the
display will show error code P40 – no SENSORPROM unit installed. If no SENSORPROM
unit has been installed, the transmitter will pick a default value which will not match the
sensor in question. This will result in false reading of all parameters.
Remedy: Install the SENSORPROM unit. If no SENSORPROM unit is available, go to the
sensor characteristics menu and enter calibration value and temperature constant value.
Both values can be found in the calibration report.
Check the reading: If temperature or density are not correct, either the SENSORPROM unit
is not correct, there are wiring faults, or the sensor has been damaged.
2. Large air collections non-homogeneously distributed in the sensor will lead to inaccurate
readings. Diagnosing air can be done via the MASS 6000 service menu or by increasing the
pressure.
•
Go to the service menu and read the values under menu driver amplitude. Under normal
conditions, i.e. water at 20 °C / 1 bar, typical driver amplitude is approximately 9 mA. If
the values are much higher and/or fluctuate more than 2-3 mA this indicates a high
damping in the system due to either air, vapors, or degassing.
•
Alternatively, close the valve after the sensor, start the pump and then increase the
pump pressure. If the zero-point becomes more stable, non-homogeneously distributed
air bubbles are in the system.
Problems with air generation may occur due to phase conditions:
1. Suction pressure of pump is too low (pump cavitation).
2. Obstructions (valves and/or blocked filters) before the sensor generate cavitation and air
generation.
3. Disolved air in the liquid is released at low pressure (can be just the pressure drop across
the sensor).
4. Volatile liquids producing air or vapors (degassing) at low pressures or high temperatures.