Liquid level monitoring for any container shape
April 2001
Sensors & Transducers
The liquid level sensing system from Trolex (Figure 1) can accurately monitor both the level and volume of the contents of any container, whatever its size and shape. It gives the customer the precise information needed to control liquid levels as required and the peace of mind of knowing exactly the volume or value of stock remaining. It operates by monitoring the pressure in the head of liquid and then linearising this result via the Trolex TX9044 programmable sensor controller in accordance with the tank shape – thus allowing the user to monitor the precise volume of liquid present in the tank at any time.
Figure 1. Volume determining system diagram
With storage tanks that are an irregular shape, whether by design or due to nonstandard usage, problems can often occur with ascertaining the exact volume of liquid inside them. The new 'intelligent' level system can overcome any such difficulties with its ability to interpret irregular patterns of volume change.
The Trolex system employs the accurate TX6114 pressure sensors (Figure 2). These units are built with a chemical and corrosion resistant housing and a ceramic diaphragm that is leak-proof and comes with an integral four active arm strain gauge. They are fully temperature compensated and have excellent linearity and long-term stability. They measure the gauge pressure of the head of liquid in the tanks and then relay the results to the TX9044 programmable sensor controller.
Figure 2. The TX6114 pressure sensor
The sensor controller then linearises the pressure input according to a preprogrammed look-up table (Figure 3) that represents the container in question, and displays the volume of the tank contents in engineering units.
The sensor controller can handle eight such inputs and has simultaneous display for all the channels. It has data communications and output ports for RS232 or RS485, as well as four output relays with adjustable setpoints, time delays, hysteresis, relay phase and latching.
Figure 3. A sample look-up table transfer function curve
The programmable sensor controllers can feed into a PC to provide consumption analysis, re-order levels, auto-fill and shutdown, and many other options. The system can also be expanded according to customer requirements to include temperature monitoring, flow monitoring, gas detection and any other parameter within the Trolex range.
Figure 4. Liquid level switches for both external and internal mounting
Trolex also manufacture a range of liquid level switches for both external and internal mounting on tanks, gearboxes, pressure vessels and boilers (Figure 4). These level switches are designed to comply with the exact requirements of the application, particularly with regard to number and position of switch contacts, process connections, materials of construction and type of electrical connection. They can also be fitted with either a temperature sensor or temperature switch.
Trolex SA
(011) 397 6958
[email protected]
www.trolex.com
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