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Hydrostatic Level Transmitter

February 1st, 2010

Level Transmitters

Water TowerA level transmitter is an electronic device that converts level measurements from a sensor to a display for a user. They can measure the level of both liquids or solids within a defined space or container (water tank, oil drum, etc), sending the data via a signal to a receiver. The receiver can be either a computer-controlled device or to a display for a user to read.

The term ‘hydrostatic’ refers to the pressure that fluids exert or transmit. So a hydrostatic sensor will measure the increase in hydrostatic pressure resulting from the increasing height of the liquid. A displaced electrical charge will accumulate, generating an output signal. Applications include measuring levels in groundwater, deep wells, water towers, rivers, sewage treatment plants and so on.

Hydrostatic Level Transmitter

Hydrostatic Level TransmitterSemrad Pty Ltd, distributor of high quality industrial level sensors, gauges, switches and transmitters, is dedicated to providing cost effective and technically advanced solutions for measuring and controlling liquid and bulksolid levels. Their products are specifically designed to perform accurately and reliably in a range of environments, including caustic, hazardous, non-contact and invasive configurations. Their years of experience have included thousands of installations worldwide in a range of industries from chemical to wastewater, mining, beverage, electronic, material handling, agriculture, textile, pharmaceutical, medical and environmental.

Semrad’s NivoPress NT-100 is a two-wire hydrostatic level transmitter that can be used in applications from liquids and masses in tanks and vessels to chemicals with dense vapour or gas layers above the surface, foaming liquids, and viscous or corrosive materials. It is controlled by a microprocessor to measure the pressure difference between the hydrostatic pressure of the liquid head above the sensor and the actual atmospheric pressure. The changes in pressure are converted into a 4-20 mA output signal. It features a ceramic diaphragm, scalable analogue output, programmable damping, secondary lightning protection, high overload capability, high accuracy (<0.2%), and a process temperature range of -30° to +100°C. The probe material is made of stainless steel, takes a power supply between 12 – 30V DC, and 8 ranges starting at 0.1 bar.

Hydrostatic Tank Gauging

December 30th, 2009

Hydrostatic Tank Gauging

Tank GaugingFluid pressure is the pressure at some point within a fluid, hydrostatic pressure being the pressure at any given point of a non-moving (static) fluid. Fluid pressure occurs in open conditions, such as the ocean, and closed conditions, such as a tank. Pressure in open conditions is usually static, as the motion of waves and currents create only negligible changes in pressure. Closed bodies of water are either static (when non-moving) or dynamic (when moving, or compressed by air).

After determining the pressure within the fluid, the pressure’s constant of integration is equal to some reference pressure within the system. The properties (such as pressure) of a fluid can be determined from a control volume analysis of a cube of water. Since the stress of all sides of the cube must be normal and equal in magnitude, the pressure gradient can be found to be linearly increasing in a potential gradient. The pressure within a fluid will increase linearly as the product of the fluid’s density and gravity.

 

Purge Control

Purge ControlHydrostatic level transmitters measure hydrostatic pressure using an air purge connection to the tank. An integral specialised airflow regulator ensures a linear response throughout the entire operating range. LiquiSeal™ or Purge Control differential pressure air flow regulators are highly refined versions of the basic bubbler air control. ‘Bubblers’ are usually a length of open pipe that extends downwards into the tank.

Semrad’s Purge Control offers continuous level measurement with pneumatic or electronic output, and is suitable for corrosive or aggressive liquids. The electronic transmitter can be applied to a maximum depth of 49m in water, while the pneumatic transmitter has a maximum depth measurement of 91m. Both have a flow rate of one nominal cubic foot per hour, and a temperature range between -18° and +82° C (though the actual process temperature limits may be significantly higher depending on the material used for the downpipe and purge airline).

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