Wednesday, May 13, 2020

Device for continous monitoring of viscosity of heavy fuel to M/E

The sensor is suspended in the oil being measured by screwing the device into a tapped hole in a stub pipe. The system uses the principle that the damping of a vibration signal is proportional to the square root of the viscosity. Not affected by vibrations or pressure and flow fluctuations. No moving parts to wear out.
The sensor comprises of a stainless steel pendulum attached to a base plate via a torsion tube. Two piezo elements are driven by an alternating signal causing the pendulum to vibrate. A second set of elements sense the torsional vibration via a feedback, and a processor measures the phase difference between the transmitted and received signals. This phase difference is processed which results in a value proportional to the square root of  the fuel oil's viscosity.
The viscosity of a fuel is dependant on the temperature; The higher the temperature, the lower the viscosity.
The output signal from the viscosity measuring device is an electrical signal between 4 and 20 mA. This electrical signal is used to control a motorised valve which allows the steam or thermal oil to the fuel oil heater.
As the viscosity of the fuel increases so the electrical signal increases. The heater temperature control valve opens further. If the viscosity falls then the signal decreases and the heater temperature control valve closes.
If the viscosity measuring device becomes inoperative, arrangements can be made to control the fuel temperature manually. The device can be bypassed, and then the heater control valve operated manually. While using the same bunker fuel, the approximate temperature to burn the fuel can be obtained from the fuel oil temperature recorded when the viscosity measuring device was operational. In the event of new bunkers being taken on, then the viscosity of the fuel must be obtained (usually given in centistokes at 50ÂșC) from the bunker receipt. The temperature to which it must be heated to obtain the desired viscosity for injection can then be obtained from a chart.
In the event of a failure of the transmitted signal to the heater control valve, the device can be used to measure the viscosity while the heater control valve is operated by hand.

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