ABSTRACT
The differential vapor pressure transmitter is a d/p cell with one of its sides connected to a temperature bulb filled with a reference fluid, while the other side is connected to the process. This way the sensor can continuously compare the vapor pressure of the process material with the vapor pressure of the sealed-in reference fluid. If the reference bulb is inserted into the process, the temperature of the reference fluid is the same as that of the process; therefore, if the two compositions are the same, their vapor pressures will also be identical. A differential vapor pressure analyzer will correctly measure binary composition under variable column pressure conditions because as the column pressure drops it will lower the boiling point on the tray. In case of distillation column control applications the bulb is placed on the control tray while the other side of the d/p cell is connected to the vapor pressure on that tray.
