WAKUI Hidekazu1 WADA Masami1 YOSHIOKA Takashi1 ANDOH Tetsuo1
Since its release in 2001, the "digitalYEWFLO" vortex flow meters employing our original spectral signal processing (SSP) technology have achieved proven track records in the market with steady increases in shipment volume. Recently, we have developed one of the world's first two-wire "digitalYEWFLO Multivariable Type" vortex flow meters with a built-in temperature sensor, which features more enhanced measuring functions while inheriting the high accuracy and reliability of the conventional "digitalYEWFLO" products.
With a temperature sensor incorporated into the flow rate sensor, "Multivariable Type" vortex flow meters enable both fluid temperature measurement and flow rate measurement simultaniously, thereby achieving multi- sensing functions such as various correction calculations based on measured temperature data as represented by steam mass flow rate calculations,.
This paper outlines the structure, functions and features of "digitalYEWFLO Multivariable Type" vortex flow meters using data from verification tests at actual users' plants.
Industrial Automation Business Headquarters
Figure 1 External View
Vortex flow meters utilize a fluid phenomenon in which frequencies of Karman vortex streets released from a shedder bar inserted in a flow are proportional to flow velocities. Our YEWFLO series of flow meters employ a system in which stress caused in a shedder bar due to vortexes is detected by means of two piezoelectric elements. These flow meters were commercialized in 1979 as general-purpose flow meters which enable measurement of liquid, gas or steam in the same detection section. Their high accuracy and high reliability have been retained in the present "digitalYEWFLO"1 products, incorporating as well a series of functional enhancements and performance improvements. As a result, the total number of units sold worldwide has already exceeded 200,000.
Recently, we have developed a "digitalYEWFLO Multivariable Type" vortex flow meter with a built-in temperature sensor, wherein a temperature sensor is incorporated into the flow rate sensor of the "digitalYEWFLO" vortex flow meter. This product enables measurement of fluid temperatures and provides new functions such as various correction calculations using the measured data.
The external view is the same design as the standard type digitalYEWFLO products, as shown in Figure 1.
Basic Principle of the Vortex Flow Meter
Frequencies f of Karman vortex streets released from a shedder bar inserted in a flow and volume flow rates Q have the following relationship:
f = K · Q K: K factor
Optimum selection of shapes and dimensions of shedder bars makes it possible for the K factor to become an almost constant value within a wide range of Reynolds numbers. As a result, the measurement of vortex frequencies f makes it possible to measure volume flow rate Q.
Flow Rate Correction Calculation
Figure 2 Cross Section of the Detector (Sensor)
The "digitalYEWFLO Multivariable Type" products use fluid temperatures measured by the built-in temperature sensor to enable various flow rate correction calculations, which are mainly as follows:
Figure 2 shows a cross section of the detector (sensor). The temperature sensor is incorporated near the lowest part of the robust flow rate sensor made of stainless steel. The temperature sensor uses a platinum temperature-indicating resistor Pt1000 (equivalent to JIS Class A). Powdered MgO which has a high heat conductivity rate is packed around the temperature sensor. One of the important applications of "digitalYEWFLO" products is the fluid measurement of gas that includes steam. In general, the specific heat capacity or heat conductivity rate of gas is low. Temperature tends to change easily in terms of both space and time. Thus, accurate temperature measurement has been considered to be difficult. In order to solve this problem, we have employed the following structures:
Figure 3 Circuit Configuration of the Signal Processing Part of the Converter
Figure 3 shows the circuit configuration of the signal processing part of the converter.
With digitized signal processing, the "digitalYEWFLO" flow meters realized the implementation of conventional analog signal processing circuits (such as an adder, a band pass filter, and a schmitt trigger) in a gate array. This allowed for the reduction of the number of parts used, thus achieving a more compact converter.
|Figure 4 Examples of Indications|
Signals detected by two piezoelectric elements are converted into digital signals via charge converters and A/D converters. The adder adds the outputs of A/D converters 1 and 2 according to a noise ratio optimum for the reduction of vibration noise. Signals processed in the band pass filter are turned into pulses in the Schmitt trigger circuit. Then, the frequencies of these pulses are calculated in the CPU to become flow rate signals.
On the other hand, the signals of the Pt1000 temperature sensor are converted into digital signals in the pre-amp and A/D converter 3 to become temperature signals in the CPU.
Flow rate signals undergo various calculations, such as the temperature correction calculation, and are output as 4 to 20-mA analog and contact pulses from the output circuit. Moreover, communication means make it possible to read not only flow rate values but also temperature values. Thus further improved convenience is realized when a "digitalYEWFLO Multivariable Type" vortex flow meter is used in conjunction with the Fieldbus communication protocol, which enables transmission of multiple measured values from a single measuring instrument (e.g., a flow meter).
The display allows for two levels of indications, providing increased information on a single screen. These indications can be selected as follows:
Upper level: flow rate or percentage (%) indication
Lower level: total rate or temperature indication (with unit indications for both)
Figure 4 shows examples of a flow rate on the upper level and a temperature reading on the lower level.
In addition, if the occurrence of an error is confirmed in the self-diagnosis function, an error number will be indicated. If a parameter has been set, its parameter number will be indicated on the upper level, while the setting value will be indicated on the lower level. Parameters can also be set using the three setting keys provided on the front of the display.
Moreover, the display can be mounted at 90-degree increments in three different directions.
Figure 5 Mass Flow Rate Measurement of Saturated Steam
|Figure 6 Streamlined Measurement (Example)|
An application using a "digitalYEWFLO Multivariable Type" vortex flow meter for the mass flow rate measurement of saturated steam is outlined below. The line in the example used a combination of a vortex flow meter, a temperature sensor, a pressure gauge and a flow rate calculator to control mass flow rates by means of temperature pressure corrections. We additionally mounted a "digitalYEWFLO Multivariable Type" vortex flow meter in the line and compared the flow rate measurement test using this vortex flow meter with the same test using the existing multiple instruments.
Figure 5 shows the results of these output comparison tests, which clearly indicate that the outputs of the "digitalYEWFLO Multivariable Type" vortex flow meter agree with those of the mass flow rate calculations made by the existing multiple instruments, including the traceability to detailed flow rate fluctuations. This comparison demonstrated that a single "digitalYEWFLO Multivariable Type" vortex flow meter can replace multiple instruments in controlling mass flow rates of steam (Figure 6).
The latest "digitalYEWFLO Multivariable Type" vortex flow meter is mainly targeted for steam applications. In the midst of growing energy control demand for environmental protection and energy conservation, "digitalYEWFLO Multivariable Type" vortex flow meters have made it possible to substantially streamline existing measurement systems. As a result, these flow meters have enabled the reduction of customers'total costs of ownership (TCO), including the initial deployment costs and maintenance costs.
The "digitalYEWFLO Multivariable Type" vortex flow meter is our pioneering product to incorporate the multi-sensing functionality which will become one of the mandatory requirements for sensors in the field network era. We are firmly committed to the continuous evolution and advancement of the YEWFLO series of products in order to meet the growing demand of our customers.
Yokogawa's vortex flow meters are long-lasting and robust, offering field-proven sensor technology and high reliability to deliver improvements in plant efficiency and reduce OPEX.
Yokogawa has been synonymous with Vortex flow meters since pioneering the industrial vortex flow meter nearly four decades ago. Over those decades, Yokogawa has continued to be at the fore front of vortex technology; so, today, Yokogawa offers a large variety of vortex flow meters, including custom made designs.