|PRIMARY VARIABLE||Differential Pressure (draft range)|
|PRIMARY VARIABLE||±0.2% of Span|
±0.1% of Span (with /HAC option)
|PRIMARY VARIABLE||300 msec (with /F1 option)|
|Figure 1 External View|
of the EJA Series
Differential pressure transmitters, which serve as the core of field instrumentation, are widely used to measure the flow rate, pressure and density of liquids, gases and steam, as well as the level of liquid in a tank.
There is strong demand from industrial plants for more accurate plant operation and labor savings in both plant operation and management as a means of improving yields. Not only are field devices required to be more precise and stable, but they must also be more intelligent in order to cut the cost of labor for plant operation and maintenance. In 1988, Yokogawa Electric released their first pressure transmitter with the BRAIN communication function-a communication protocol in which the 4-20 mA analog signal is mixed with digital signals. Since then, they have continued to release newer models of these pressure transmitters as well as striving to produce increasingly intelligent pressure transmitters, such as the DPharp series.
Recently, the focus has turned to the standard fieldbus (with its multidrop connection and full digital transfer) that will replace the conventional BRAIN communication with 1-to-1 connection. This paper introduces the EJA series pressure transmitter that supports the fieldbus protocol advocated by the Fieldbus Foundation. Figure 1 is an external view of the transmitter.
DESIGN CONCEPTS AND FEATURES
We now describe the design concepts and features of the fieldbus-enabled EJA series pressure transmitter.
Figure 2 Components of the Transmitter
Easy Connection for Communication
The EJA series transmitter has three blocks for connecting itself to other devices: one resource block and two analog input blocks. These function blocks are configured using the standard parameters specified by the Fieldbus Foundation. Consequently, users can use the EJA series transmitter without needing device information unique to the transmitter. We believe that the ease at which the transmitter can be connected to the fieldbus is its key strength. It also goes without saying that the specific functions of the EJA series transmitter are also possible if that transmitter’s own device information (Device Description, or DD) is used.
- High Precision, Stability and Reliability
As an EJA series device, the fieldbus-enabled transmitter model inherits the existing industry-proven features of that series, namely, the high-precision, high-stability and high-reliability characteristics.
All key components of the transmitter are Yokogawa originals that have been fabricated under strict quality control. The fabrication process involved both automation and mechanization in order to manufacture products with less product-to-product variation in performance.
The conventional analog transfer technology is designed to output only one signal for the control information. Fieldbus technology, on the other hand, permits the use of multiple information items such as status information, alarm information, the PV (primary value) and the SV (secondary value).
The EJA series transmitter outputs the PV value (the value for differential pressure) and SV value (the value for static pressure), along with the status information. It can also transmit alarm signals if the process value exceeds the limits (setpoints) for plant operation. Furthermore, the transmitter can send out alarm signals once the operating ranges defined in the transmitter capsule specifications are exceeded or if it detects any failure as a result of the sensor’s internal judgment or the memory status.
- Compatibility with the Existing Capsules
The new model is compatible with existing EJA series transmitters, which means that a conventional model based on the BRAIN (4-20 mA analog transfer) protocol can be changed to a fieldbus-enabled model by simply replacing its converter.
- Reduction in Instrumentation Costs
Bus connection enables users to reduce the cost of instrumentation even below that of the conventional 1-to-1 connection. Furthermore, an additional transmitter can be easily installed next to an existing fieldbus-enabled device at any time in the future by connecting an additional cable from the device to the transmitter.