Linearising to obtain volume from level measurement
February 2004
Level Measurement & Control
DSP, Micros & Memory
A company that produces various liquids had a need for an indicator that could display, in litres, the amount of solvent in a tank. Because the solvent is corrosive, an ultrasonic level sensor was used. The customer calibrated this sensor to produce 4 mA of current when the tank was empty, and 20 mA of current when the tank was full. This signal was to be measured by a 4 to 20 mA meter, calibrated to read in litres. Any one of Red Lion's 4 to 20 mA meters would have worked for this application, if the tank had parallel sides, but this tank was cylindrical, and laying on its side. This meant that while the signal measured was linear to depth, it was not linear to litres of liquid in the tank. (There is more volume per cm of depth in the middle of the tank, compared to very little volume per cm of depth near the top and bottom.)
Because this signal is non-linear, an IMP with the Lineariser option was best suited to fit this customer's needs. Instead of selecting a reading of 0 at 4 mA, and 2000 at 20 mA, 10 points along the input curve were entered. Where the measurement could have been out by as much as 200 litres with single-segment scaling, nine-segment scaling (or 10 points) makes it possible to reduce the error induced by the shape of the tank down to a few litres.
The customer had two choices when scaling the meter: Pro 1 or Pro 2. In Pro 1, the unit measures the 4-20 mA signal at each point, and pressing the 'P' key automatically enters the input signal for the keyed-in gallon amount. In Pro 2, both the gallon amounts and the signal level are keyed in, so these values have to be known prior to scaling the unit. This customer had the manufacturer of the tank furnish the values for him, so he opted to use Pro 2.
The customer also wanted an alarm output to turn on a pump when the tank was almost empty. Alarm 1 was programmed to begin filling the tank when the level fell to 250 litres, and to keep filling it until it was at 1900 litres. This was done by programming Alarm 1 as a Lo-acting alarm with a value of 250, and a hysteresis of 1650. After the unit was programmed, the customer locked out all the parameters to prevent anyone from entering inadvertent settings.
Further reading:
A fresh approach to dairy processing
VEGA Controls SA
Level Measurement & Control
Ensuring the quality and safety of milk throughout the production process is of the utmost importance in the dairy industry. The VEGABAR pressure transmitters are suitable for hygienic applications. They are an asset in the dairy industry and have been used with success for measuring the milk level and the process pressure in storage tanks.
Read more...
A new era in radiometric level and density measurement
Mecosa
Level Measurement & Control
The LoopSeries LB 430 radiometric detector from Berthold Technologies has a revolutionary power solution and sets new standards in level and density measurement.
Read more...
Level measurement of an acid dosing tank at a WWTP
Level Measurement & Control
Ferric chloride and other acids are essential chemical substances in water and wastewater treatment. To control the dosing of acid solutions, an Australian wastewater treatment plant uses a special container to store, mix and add these chemicals. The company opted in favour of KROHNE’s OPTIWAVE 1540 radar level transmitter
Read more...
Level measurement of leachate from sewage sludge humification
Level Measurement & Control
A municipal utility in eastern Germany operates a state-of-the-art wastewater treatment plant with sustainable sludge treatment. The ultrasonic signal was being partially deflected by the wind, leading to frequent false measurements and inefficient process workflows. The problem was solved by replaced the ultrasonic level sensor with KROHNE’s OPTIWAVE 1540 non-contact radar.
Read more...
Groundbreaking measurement system
Mecosa
Level Measurement & Control
Berthold Technologies has launched the LoopSeries LB 430, an innovative, industry-leading measurement system designed to enhance operational efficiency with advanced level, density, and level switch capabilities.
Read more...
Level measurement of a water sump at a sewage treatment plant
Level Measurement & Control
A major city council in South East Queensland, Australia maintains and operates a wastewater treatment plant (WWTP) for municipal, industrial and agricultural wastewater. Due to the risk of flooding, the water sump must be continuously monitored. The solution is KROHNE’s OPTIWAVE 1540 radar level transmitter.
Read more...
Simplicity in measurement
Endress+Hauser South Africa
Level Measurement & Control
Endress+Hauser’s new 80 GHz compact radar range is designed to help customers reach their compliance targets through simple yet efficient measurement solutions.
Read more...
Arduino platform with Analog Devices technology for flexible industrial control
Altron Arrow
Editor's Choice DSP, Micros & Memory
Software-configurable systems enable industrial OEMs to deliver unprecedented flexibility to the factory floor, while simplifying product complexity.
Read more...
Case History 196: Unstable condensate level control.
Michael Brown Control Engineering
Editor's Choice Level Measurement & Control
The operators in a petrochemical refinery were having great trouble in trying to stabilise the condensate level in a vessel, and this was adversely affecting other loops downstream. Several unsuccessful attempts had been made to retune the controller.
Read more...
Non-contact level measurement for hygienic and industrial applications
ifm - South Africa
Level Measurement & Control
The LW2720 radar level sensor from ifm sets new benchmarks for speed and accuracy.
Read more...
printer friendly version