Screen Differential Control

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What is screen differential control? This is a control application commonly found at utility plants located on rivers, lakes and other large bodies of water and at industrial facilities where a large amount of cooling water is used. Screen differential control and monitoring is needed to prevent damage to rotating screens caused by excessive pressure being applied by debris collecting on the screens.

Screen Differential Control 

Screen Differential Control


A typical cooling system consists of two or more sets of rotating screens. When the differential across a set of screens reaches 15 cm (7 inches), an alarm is activated. If the differential reaches 25 cm (10 inches), the screens start to rotate and back wash pumps are started initiating a backwash procedure to clean the screens of any accumulated debris.

Differential is measured by monitoring the back pressure created by displacing water in sensing lines using regulated air flow. Lines are located upstream and downstream of each screen.

Upstream and downstream pressures are monitored by a recorder set up to read differential flow. Transmitter outputs are fed into the recorder so operators have tide reference, individual screen differentials with alarms and auto start for wash pumps. These contacts are fed into the screen logic by the recorder alarm option.


DPharp was recently selected for this application by a major Texas electric utility company when they redesigned their screen differential monitoring and control system. The company selected DPharp over their plant standard because of its ability to withstand plant air applied to sensing lines during blowback operation--without having to be taken out of service, and with no shift in calibration after completion of blowback. Transmitters have been in operation since November of 1996, and plant maintenance personnel are very pleased with their performance.

A simplified screen differential monitoring diagram is shown below. Solenoid valves or a timer are used to initiate automatic blowback operation once a day. DPharp monitors the differential across the rotating screens.

Main Features of 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)


  • Eau et traitement des eaux usées

    Yokogawa has been providing control solutions for sustainable water production by developing more energy-efficient technology, helping to reduce the carbon footprint of operations, and building rock-solid products that protect the environment from contaminants. With our leading-edge technology and extensive application know-how, we work with you to provide sustainable water solutions that boost your business and add high value throughout the plant lifecycle. Our technology and products improve the performance of plants and ensure that they can operate competitively in today's water markets, and also reduce their running costs. Yokogawa supports a wide range of water control applications in both the municipal and industrial water markets.

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  • Eaux industrielles

    Industrial water is used in all industrial plants such as power generation stations, refineries and petrochemical plants. Yokogawa’s single control platform handles all water and wastewater control processing integrated with the main process.

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  • Traitement de eaux usées

    Wastewater treatment plants use many motors, pumps, blowers, etc., and so it is important to reduce their electricity consumption in order to reduce running costs. Yokogawa provides optimum control solutions to improve energy efficiency.

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  • Traitement des eaux

    Yokogawa provides optimum solutions to improve the reliable operation of water treatment plants. These solutions include sophisticated technologies, unsurpassed product quality, and extensive application know-how throughout the lifecycle.

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Les produits et solutions liés

  • EJA110A

    Transmetteur traditionnel de pression différentielle basée sur la série EJX-A.

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  • EJA110E

    Transmetteur traditionnel de pression différentielle basée sur la série EJA-E.

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  • EJX110A

    Transmetteur traditionnel de pression différentielle basée sur la série EJX-A.

    Voir plus

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