ITOU Akio1 MIMURA Shin-ichi1 KOYAMA Etsutarou1 ODOHIRA Tetsu1 NIKKUNI Masaaki1 MIYAUCHI Tatsuhiko2
We have developed the EJX910 multivariable transmitter, an all-in-one instrument that integrates the functions of a differential pressure transmitter, a pressure gauge, a thermometer and a flow computer, while featuring high performance and space-saving design. The transmitter employs a unique flow rate calculation method, achieving a mass flow calculation cycle of 100 milliseconds. By adopting a Reynolds number compensation algorithm, etc., all flow calculation parameters were optimized and a mass flow accuracy rate as high as 1% was achieved. Furthermore, EJX910 complies with a wide range of primary devices, including orifices, nozzles and venturi tubes, and various types of fluid, including general fluids, steam tables, and natural gas. Application information, such as the primary devices and fluid data required for mass flow calculation, is input using the EJXMVTool, a mass flow parameter configuration tool that runs on a PC and is downloaded to the transmitter by means of field communication. A field test performed on a British natural gas test line showed an excellent mass flow measurement accuracy of 1%.
|Figure 1 External View
When evaluating mass flow rates using a primary device such as an orifice or nozzle in a differential pressure flow meter in order to make fluid density compensations, the upstream pressure (static pressure) and fluid temperature are measured in addition to the output of a regular differential pressure transmitter. In the past in such cases, a differential pressure transmitter, a pressure transmitter, a temperature converter and a flow computer were all separately required. The DPharp EJX series of differential pressure transmitters developed by Yokogawa in 2004, can simultaneously measure both differential pressure and static pressure using an advanced form of silicon resonant sensors that comprise the multi-sensing function. Recently, we have developed the EJX910 multivariable transmitter as a new model that incorporates this series' functions to full advantage. The EJX910 integrates the functions of a differential pressure gauge, a pressure gauge, a thermometer, and a flow computer into a single instrument, thereby achieving high space efficiency and multifunctionality.
A Reynolds number compensation algorithm and other means have been adopted for the mass flow rate calculation of this transmitter to optimize all flow rate calculation parameters and achieve high-precision mass flow rate measurement. In this paper, we will focus on the functions related to mass flow rate calculation, one of the features a multivariable transmitter has to offer. Figure 1 shows an external view of the EJX910.
The EJX910 multivariable transmitter serves as a differential pressure gauge, a pressure gauge, and a thermometer (with an external temperature sensor). In addition to this multifunctionality, the fluid density compensation function provided by the transmitter itself and the PC-installed EJXMVTool's mass flow parameter configuration tool enable high-speed, high-precision mass flow rate measurement. The EJX910 supports a number of flow rate standards and a variety of fluid types as target applications. Moreover, the EJX910 can be applied to integrated flow rate measurement and various diagnoses that use many process variables (differential pressure, static pressure, temperature, etc.).
|Figure 2 Example of Mass Flow Rate
Measurement Using Orifice
|Figure 3 Mass Flow Rate Measurement
Figure 2 shows an example of measuring mass flow rates from orifices and temperature sensors installed in a process. The EJX910 measures the difference between the upstream and downstream pressures of the orifice placed in the process, the upstream static pressure and the fluid temperature. Then the transmitter calculates the mass flow rate from these measured values.
Figure 3 shows a configuration of a mass flow rate measurement system. Application information necessary for flow rate calculations (primary device and fluid information) is input using the EJXMVTool mass flow parameter configuration tool running on a PC. This information is then converted into parameters that can be perceived by the transmitter and downloaded to the transmitter by means of field communication.
Figure 4 shows a block diagram of a mass flow rate measurement system comprising the EJX910 and EJXMVTool. Differential pressure, static pressure and temperature measured by the EJX910 can be directly output as process variables. The system performs fluid density compensation calculations according to the following equation to determine the mass flow rate.
|Figure 4 Mass Flow Rate Measurement Block Diagram|
Qm: Mass flow rate
C: Discharge coefficient
β: Beta ratio (d/D)
d: Bore of primary device
D: Pipe inner diameter
ε: Gas expansion factor
∆P: Differential pressure
ρ1: Fluid density
For this purpose the system employs a unique method of calculation that minimizes the transmitter's calculation load, and achieves a flow rate calculation cycle of 100 milliseconds. In a simplified method of flow rate calculation, the parameters in Equation (1) are treated as fixed values, resulting in large mass flow rate calculation errors as shown in Figure 5. The EJX910 performs optimized calculations in real time using dynamically changing parameters, thereby realizing a high flow rate accuracy of 1%. More specifically, Reynolds number corrections are made to the discharge coefficient (C) according to changing measured values. The gas expansion correction factor (ε) is corrected against the effects of adiabatic expansion of gases. In addition, the fluid density (ρ1) is corrected for static pressure and temperature variations.
|Figure 5 Comparison of Mass Flow Rate Errors between
Fixed-parameter Calculation and Optimized Calculation
The primary devices that the multivariable transmitter is compatible with, i.e., orifices, nozzles and venturi tubes, comply with a number of flow rate standards. In addition, a fixed mode is available to set desired values to the discharge coefficient and the gas expansion correction factor. The transmitter can handle a wide variety of fluid types as described below:
|Figure 6 Structure of EJXMVTool Software|
Figure 6 shows the structure of the EJXMVTool mass flow parameter configuration tool used to set mass flow rate application information.
|Figure 7 Settings of Primary Device Information||Figure 8 Settings of Fluid Density and Viscosity|
As explained below, the operating screens of EJXMVTool have been designed in association with specific applications.
|Figure 9 Verification of Results of
Flow Rate Parameter Calculations
Figure 10 Results of an Actual Natural Gas Flow Test
Figure 10 shows the results of an actual flow test performed on a British natural gas test line. The test results show a mass flow rate measurement accuracy level as excellent as 1%. Users have also highly evaluated the EJX910 in other actual flow tests.
In future we intend to further accumulate experience in mass flow rate measurement using multivariable transmitters, while broadening the range of applications to encompass an even greater variety of primary devices and fluids. In addition to mass flow rate measurement, we will further develop fluid level measurement and multivariable measurement-based process diagnosis.
This transmitter precisely measures differential pressure, static pressure, and process temperature; then uses these values in a high-perfomance on-board flow computer to deliver fully compensated Mass Flow.
The accurate and stable measurement of process pressure with Yokogawa Pressure Transmitters supports the safe, reliable, and profitable operation of your plant.