Identification of the transfer characteristic of a differential pressure transmitter using non-parametric methods

Previous studies have shown that the ´noise´ components of flow measurement signals made with an orifice plate/differential pressure system contain useful information regarding the status of both the measurement system and the associated process plant, which can be recovered by signal analysis methods. The objective of this paper is to demonstrate that to recover and extract this information: (i) the maximum amount of information regarding the process which is available at the interface between the process and the sensor must be gathered, (ii) this requires the sensors and transmitters to have a wide frequency response and, (iii) signal analysis methods provide a means for analysis of this data to monitor changes in the status or condition of the measurement system as well as the associated process plant. The study presented describes a relatively simple and repeatable method for determining the transfer characteristic of a transmitter. It also shows that the characteristic is influenced by (i) the nature of the process fluid, (ii) the length of the process connections, (iii) partial blockage of the process connections and (iv) changes in the stiffness or status of the diaphragm which forms the interface between the process and the sensor.