Electricity + Control October 2015

PRESSURE + LEVEL MEASUREMENT

IS afe piezoresistive Series 26 Y Ei level sensors are suitable for environments

• Ameasurement systemhas been developed that enables customers to call up current filling levels and previous purchase orders for oil and gasoline tank installations. • Customers are alerted via sms or email if the filling level falls below a certain limit. • Customers can call up their data anywhere, at any time, and are therefore able to plan their purchasing efficiently.

subject to a high explosion hazard.

take note

The benefits of using this system are derived from the combination of measurement and remote transmission. While developing the proposed solution, Keller‘s pressure measurement experts were able to draw on experience garnered from customers in the water management sector, where similar concepts are used to monitor groundwater and river water levels. The underlying technology makes it possible to develop special solutions with great flexibility and speed. For customers in the water management sector – to take one example – a GSMmodem that sup- ports data exchange via email, SMS and FTP, has been developed. The GSM-3 variant (modified at the customer’s request) which offers the option of SMS communication with consumers, has been devel- oped. Customer surveys have confirmed that this is the most reliable version, and the one that customers prefer. More so than email, SMS messages guarantee that customers are informed promptly; they are spam proof and can be personalised. Especially in offices, emails could be called up by different individuals whomight not all be authorised to make a purchase decision, thus wasting valuable time. Intrinsically safe and temperature resistant The GSM-3 comprises the modem itself and what is known as the SB box, to which as many as three pressure transmitters (with voltage outputs of 0,5…4,5 V) can be connected. The box contains three built- in safety barriers (SBs). These circuits make it possible to process the electrical measurement signals to gas stations, where an electrical spark could cause an explosion due to the gases contained in the atmosphere. This is why any pressure transmitter that performs measurements in an environment of this sort must be intrinsically safe. The safety barrier limits the electrical power produced by the measurement system within the area subject to explosion hazards (EX area).The GSM-3 itself may only be installed outside of the EX area. As part of the complete package, level sensor cables used to transmit the measurement signals, are supplied. Intrinsically Safe (IS) 26 Y Ei level sensors are used for the systems at gas stations, whereas the conventional version is used for heating oil tanks in locations not classified as EX areas. The transmitters in these devices are based on the piezoresistive silicon measuring cell invented by the company’s founder and chief executive offi, Hannes W Keller, at the end of the 1960s. The slight mechanical deformation caused by the pressure on a piezoresistive element in the sensor triggers a change in resistance which, in turn, produces the electrical voltage that is used as the measurement signal. In Series 26 Y, which includes the level sensor, the temperature error (as it is known) is compensated electronically.

The GSM-3 comprises a modem and what is known as the SB box, to which as many as three pressure transmit- ters (with voltage outputs of 0,5…4,5 V) can be connected.

One-stop expertise These products guarantee long service lifetimes, even in an aggres- sive medium such as gasoline, because of their robust stainless steel housing (degree of protection: IP68) and a design whereby the silicon measuring cell is protected against the measured medium by a stainless steel diaphragm. Originally, the plan was only to purchase the pressure sensors from Keller, as the project proceeded, it became clear that the com- pany has expertise in the the remote transmission of measurement data, as well as in measurement technology. They were therefore used to deliver the entire package. Conclusion Depending on each system’s location where each system is deployed, either the conventional 26 Y level sensor or the intrinsically safe 26 Y Ei version is used, together with the GSM-3 transmission unit and the cables (whose lengths vary according to on-site conditions). Final assembly and installation of the systems takes place at the custom- ers' premises.

Marcel Gautschi, Dipl. El.-Techniker TS (M.Sc. Electrical Engineering) Electronics- & Software Development. Enquiries: Instrotech on 010 595 1831 or sales@instrotech.co.za

October ‘15 Electricity+Control

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