Low Flow Cut-off

Introduction

Fig.1: Low Flow Cut-off
Fig.1: Low Flow Cut-off

One of the most common applications for differential pressure transmitters is flow measurement. A differential pressure transmitter can be placed across many types of primary flow elements like orifice plates, pitot or venturi tubes to measure flow. Primary flow elements create a pressure drop (square root proportional to flow).

Flow proportional output signals from a differential pressure transmitter are possible through integral square root extraction. The square root function of differential pressure has extremely high gain at low flow rates leading to large output changes representing low changes in flow rate at the bottom end of the measurement range. Output signals can become erratic at low flow rates due to high gain. Host control systems can experience difficulty controlling flow rate based on a highly fluctuating input signal from the square root extracted differential pressure. DPharp differential pressure transmitters have some unique signal conditioning features to eliminate instability at low flow rates.

Application

Flow rates above 20% of maximum flow produce a large square root extracted differential pressure signal for a given change in flow rate. Flow rates around 5% of maximum flow produce a small square root extracted differential pressure signal for a given change in flow rate (See Fig.1). High gain in the low flow rate operating area amplifies any inherent noise or changes in flow rate leading to pressure transmitter output instability.

Solution

Fig2
Fig.2

 

Fig3
Fig.3

DPharp has a software capability to stabilize output signals at the low end of a flow measurement range minimizing erratic output signals. An integral low cut mode features a user programmable transmitter output and set point to change the output to a linearto- pressure (Linear) or zero (Zero) status. The flow rate set point at which an output transition occurs is programmable from 0 to 20% of full scale flow. Fig.2 shows Linear and Zero output modes set at 5 % low cut mode.

Hysteresis is incorporated into the low cut mode such that when the actual flow rate is equal to the low cut set point that output oscillation will not occur. Hysteresis is fixed at a nominal 1% of full scale flow. Fig.3 details how the hysteresis affects the pressure transmitter output.

 

 

Main Features of DPharp

DPharp
DPharp

EJA110A Digital Solution

  • Best-in-class performance
  • ±0.03% Overpressure calibration protection
  • ±0.1% per 5 years long term stability
  • 100:1 turndown
  • ±0.065% accuracy

EJX110A Premium Value

  • ±0.1% per 10 years long term stability
  • 200:1 turndown
  • Best-in-class high accuracy, 0.04%
  • Multi-sensing output
  • Multi-variable transmitter as EJX family line-up
  • Safety as standard (IEC 61508)

Industries

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    Chemical plants rely on continuous and batch production processes, each posing different requirements for a control system. A continuous process calls for a robust and stable control system that will not fail and cause the shutdown of a production line, whereas the emphasis with a batch process is on having a control system that allows great flexibility in making adjustments to formulas, procedures, and the like. Both kinds of systems need to be managed in available quality history of product, and to be able to execute non-routine operations. With its extensive product portfolio, experienced systems engineers, and global sales and service network, Yokogawa has a solution for every plant process.

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    In the mid 1970s, Yokogawa entered the power business with the release of the EBS Electric Control System. Since then, Yokogawa has steadfastly continued with the development of our technologies and capabilities for providing the best services and solutions to our customers worldwide.

    Yokogawa has operated the global power solutions network to play a more active role in the dynamic global power market. This has allowed closer teamwork within Yokogawa, bringing together our global resources and industry know-how. Yokogawa's power industry experts work together to bring each customer the solution that best suits their sophisticated requirements.

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  • Specialty & Fine Chemical

    Yokogawa has long served customers in the specialty and fine chemicals market. With a market leading batch solution that offers the best in class reliability and flexibility as well as industry experts who understand the complex requirements in designing a batch solution, you can be assured that in your partnership with Yokogawa you will have a system that will enable you to produce products that meet your customers’ needs in the future while maintaining safety and regulatory compliance.

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    • Yokogawa integrated control/monitoring maximize topsides operations productivity and availability
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    The upstream industry includes offshore and onshore activities including wellhead automation, fractionation, completion, and separation to recover and prepare underground or underwater crude oil and natural gas.

    As petroleum is brought to the surface, it must be separated prior to transport. Primary and secondary separation stages commonly distribute gas flow, water flow, and oil flow in three phase separation. Gas movement requires pipeline and can include a fractionation process in the upstream stage prior to movement. Liquids can be placed into a tanks or pipelines and sent for processing, requiring accurate level measurements.

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  • Water & Wastewater

    All water, regardless of its source, has value. However, with water resources being finite, a focus on "One Water" is necessary to maximize every drop within the water system, ensuring a stable supply of clean and safe water.  As we consider current and future needs, planning and implementation are critical for long-term resilience and reliability, meeting both community and ecosystem demands. Yokogawa believes water is a human right for all. Thus, contributing to a sustainable water cycle is one of our Sustainable Development Goals (SDGs).

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  • Wellhead & Separation

    The wellhead provides the structural and pressure-containing interface for the drilling and production equipment. The surface pressure control is provided by a christmas tree, which is installed on top of the wellhead. Isolation valves and choke equipment physically control the flow of well fluids when the well goes into production. Various automation packages are added to locally or remotely monitor, control and optimize production from each well or multi-well pad. Oilfield separators employ a pressure vessel to separate well fluids produced from oil and gas wells into gaseous and liquid components which are then transferred to pipelines or localized storage depending on the areas infrastructure.

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