Using Keller Sensors in a Remote Level Monitoring System

AVIA Osterwalder St. Gallen AG serves more than 120 filling stations in eastern Switzerland. This company also supplies engine fuel and other types of fuel for corporate and private clients. For many years, AVIA has been using the EasyOil system, which allows its clients to remotely monitor the fill level in tanks containing oil and gasoline. During the recent relaunch of the EasyOil system, AVIA turned to the specialists at KELLER AG für Druckmesstechnik for assistance, asking them to conduct an expert review of the measurement technologies.

In brief, EasyOil includes a system for measuring the fill level of a fuel tank, a GSM modem that allows transmission of the obtained level data via the mobile phone network, as well as software developed jointly with Fredell GmbH Informatiklösungen that enables users to retrieve information about the current fill level and previous fuel purchases. Additionally, if the level in the tanks drops below a certain value (which can be freely set), users receive an SMS or email notification. By responding to these messages, clients can immediately place an order for delivery with AVIA. Since data can be accessed anytime and from anywhere, users can plan purchases more efficiently. For example, it is possible to buy fuel when oil prices are low or when a fuel tanker is nearby.

This service not only helps private clients who are too busy at work and might return home after a long day to an unheated house because they forgot to order fuel. The main advantage is that this system offers significant economic benefits to production managers in companies, as well as property managers who must coordinate fuel supply for numerous sites. Gas station operators and their consumers (i.e., large fuel companies) can also benefit from a system like EasyOil. The head of marketing at AVIA emphasizes: “By offering the EasyOil service to our clients, AVIA stands out advantageously among competitors.” She adds: “There is plenty of evidence that our clients appreciate the convenience provided by this service: for example, in the last three years, 80% of users whose contracts allowed them to purchase from other suppliers preferred to regularly order domestic heating fuel from us.”

Thus, over ten years since its launch, the EasyOil system has proven itself as a win-win model: users value its convenience and transparency, and AVIA gains loyal customers in an extremely competitive fuel market. Since 2013, the company has offered users updated contract models that are even more transparent and easy to use.

Advanced Technology

Even before this redesign, the technology behind EasyOil had already been updated. When AVIA was looking for a suitable supplier of both measuring instruments and GSM modules, their attention was drawn to the Winterthur-based company KELLER AG für Druckmesstechnik. KELLER operates worldwide, and about 10% of their sales revenue comes from applications requiring pressure sensors for level measurement. Such an application is technically feasible because pressure at a certain depth is proportional to the fill level. Thus, the measured pressure value can then be used for highly accurate electronic level calculations. Taking into account the shape of the tank, it is also possible to calculate the volume of its contents in liters.

The advantages of EasyOil are based on the combination of measurement and data transmission capabilities. Working on the task set by AVIA, KELLER specialists were able to leverage experience gained from working with clients in the water supply sector, where similar technologies are used to measure groundwater levels and river levels.

The technology described below was developed by KELLER without involving external specialists, so the company can now quickly develop flexible custom solutions for clients in this area.

For example, for clients in the water supply sector, KELLER developed a GSM modem supporting data exchange via email, SMS, and FTP. Currently, KELLER supplies AVIA with the GSM-3 model (modified according to customer requirements), which also offers the possibility of user communication via SMS. “Surveys of our clients confirmed that this version is the most reliable and is preferred by users,” AVIA states. Unlike email, the SMS alert system guarantees that the client receives information promptly; it is protected from spam and can be personally customized. “Email messages, especially in offices, can be handled by different employees, not all of whom may have the authority to place orders. All this can lead to unwanted time loss.” 

To ensure that orders are planned efficiently, the software allows visualization of the current tank fill level, consumption, and order history through a web portal. The ability to customize graphical display options guarantees a clear and accessible presentation of data for users.

Intrinsically safe and high-temperature resistant device for explosive zones (EX)

GSM-3 combines a modem and a protective enclosure, to which up to three KELLER pressure transducers (with a voltage output of 0.5…4.5 V) can be connected. The enclosure includes three built-in fuses. The electrical circuits allow sending an electrical signal to the gas station, where an electric spark due to increased gas concentration in the atmosphere can cause an explosion. For this reason, any pressure transducer used in such an environment must have an intrinsically safe design. The fuses limit the current generated by the measuring system in explosive environments (EX). The GSM-3 device itself can only be installed outside the explosive zone. KELLER also includes cables for transmitting the measurement signal from the sensors to the modem in the complete delivery set.

In the EasyOil system at gas stations, KELLER uses intrinsically safe level sensors 26 Y Ei; when used in tanks with domestic furnace oil, where the environment is not explosive, the standard version of the same device is applied. As with all other pressure measuring devices produced by KELLER, the sensors in this device operate based on a piezoresistive silicon measuring cell, invented by the company founder and CEO Hans W. Keller in the late 1960s. Currently, KELLER is one of the world’s leading manufacturers of piezoresistive pressure sensors. A slight mechanical deformation caused by pressure on the piezoresistive element in the sensor leads to a change in resistance, which in turn generates an electrical voltage used as the measurement signal. In the 26Y series sensors, including level transducers, temperature error is compensated electronically.

Comprehensive expertise

Thanks to extensive experience and proven products, KELLER can produce pressure transducers for the EasyOil system with an excellent price/performance ratio. Thanks to a robust stainless steel housing (protection class: IP68), as well as a design where the measuring cell is protected from the measured medium by a steel membrane, these devices have a long service life even when used in aggressive environments such as gasoline.

“Initially, we planned to purchase only pressure sensors from KELLER,” recalls the EasyOil equipment specialist from AVIA. “But as the project progressed, it became clear that KELLER has vast experience in remote transmission of measurement results, as well as knowledge in measurement technologies. This prompted us to entrust KELLER specialists with the creation of the entire equipment complex.”

Depending on where the EasyOil system is intended to be installed, AVIA purchases from KELLER either standard level sensors 26Y or the intrinsically safe version 26 Y Ei, as well as the data transmission unit GSM-3 and connecting cables (length varies depending on installation conditions). Final assembly and installation of the system, as well as software configuration, are carried out by AVIA. The company speaks very positively about this project:

“Customer feedback is very positive. We are completely satisfied with the excellent performance and reliability of the system. Our cooperation with KELLER is productive and mutually beneficial – moreover, their specialists supported us in implementing our special projects. That is why we hope for further long-term cooperation with KELLER and their support of our new sales and marketing projects based on EasyOil.”

Advance fuel procurement when the fuel truck is nearby – the system allows AVIA to offer this service to its customers.