Autonomous measuring systems with data transmission via GPRS (GSM-2)

author Marcel Gaudji

KELLER AG 7/2009

There is a widespread need for autonomous measurement systems, for which data logger devices were usually used. In this case, we do not conduct constant monitoring of the object of interest, but obtain a certain historical picture of the events taking place. Measuring instruments did not have the capability for continuous monitoring. The use of mobile cellular networks and the internet has now made it possible to connect all measurement points in one place!

Modern systems allow saving

Modern measurement systems provide the following advantages by using components and technologies already developed for mass applications. A typical example is the use of cellular operator networks for data transmission. Coverage areas and signal levels in these networks are constantly improving, and the cost of calls and data transmission is constantly decreasing and becoming simpler, so the GSM-2 system can be used not only for remote objects but also for nearby points. The cost of data transmission is much lower than the constant use of hired workers to take readings. Moreover, the measurement system itself with a data transmission module does not significantly exceed the cost of systems with a data logger. The cost of data transmission via email today is very cheap, especially if you use a tariff without a subscription fee.

Data transmission via email or SMS is the simplest and most modern solution. A regular mobile phone is suitable for reading data via SMS, or you can use a PC with internet access and receive data by email.

Data processing: Computer as a data logger

The heart of the measurement system is the GSM-2 DataManager program with a user-friendly interface. The program collects data, monitors, and manages several measurement stations (GSM-2) simultaneously, and is also used to display on the screen and analyze data, which can be stored in open formats.

Data received from the GSM-2 GPRS transmitter (e-mail/SMS) is constantly read and recorded in the DataManager database. We get unambiguous information about the correct operation of all measurement systems. In case of an error, i.e., absence of received data, we see it on the computer or receive a notification via SMS or email. All measurement points can be displayed graphically, as well as their geographical location shown on the screen.

Settings for an individual measurement station can be made on the computer and new data sent via email to the GSM-2 module.

Applications

The GSM-2 module is ideal for objects where it is not possible to provide continuous power supply to devices. Typical applications: mobile equipment tanks (auto and rail tanks), construction sites, measurement of groundwater and wastewater levels.

GSM-2 for measuring groundwater levels

Measuring groundwater levels or the levels of lakes and rivers is a fairly common task for government institutes, private energy companies, and water utilities. For these purposes, Keller developed the GSM-2 module together with measuring sensors. The GSM-2 module design is specially made for installation in 2-inch diameter pipes. The module meets all the requirements for equipment that must operate for a long time in field conditions. Measurement stations are mostly located in remote points and do not have access to a constant power source. In other words, systems operating on batteries for a long time are required. In addition, all equipment must be resistant to low temperatures, short-term flooding, and high humidity. Moreover, the system must be protected from thieves and vandals.

Quick and convenient installation

The GSM-2 module fits entirely into 2-inch diameter pipes. The transmitting part is covered with a protective cap; no complex antenna installation system is required. The entire installation takes a few seconds.

After installation, the GSM-2 module transmits information about its name and settings, about the measurement station to the DataManager system, which immediately and automatically starts working.

For system security and better signal reception, an external antenna can be used.

For example, in Finland, the best place to install the GSM-2 module is an anthill. This provides excellent protection not only from thieves and vandals but also raises the ambient temperature for the module, which is important for battery life.

Facts

• Battery life (up to 10 years)
• Quick and convenient installation
• Various interfaces for sensors
• Free software
• Competitive cost

Technical information

The DataManager program performs data acquisition and viewing, manages measurements (graphical display, … etc.)

The electronics and battery of the GSM-2 module are housed in a waterproof stainless steel case with a diameter of 48mm.

The top part, designed for use in 2-inch pipes, is closed with a cap and contains the antenna and an interface for configuring the measurement system. The measuring sensor is connected to the module from below. Depending on the environmental conditions and settings, the module can operate on a single battery for more than 10 years! The module is simply turned on when necessary (i.e., to receive input data or send measurement results).

Measurement results obtained over a specified period are stored in the GSM-2 module and sent via a single message (e-mail/SMS)

At the same time, certain events, such as a sharp increase in level and exceeding set values (minimum and maximum), lead to immediate data transmission via an additional SMS or email message. Along with this, data on battery capacity, antenna signal level, and other additional information are transmitted.

GSM-2 module for data logging and transmission with connected level and temperature transducer

Inputs for various sensors and applications

In addition to the RS485 interface, through which we receive signals from KELLER pressure and level sensors, the module itself is equipped with atmospheric pressure and temperature sensors. Thus, liquid level measurement is carried out using the so-called AA (absolute-absolute) technology. The advantage of this method is the complete absence of a capillary tube connecting the level sensor to the atmosphere. With this method, the system is not sensitive to humidity, and there is no risk of mechanical damage to the capillary. All this makes the measurement system robust, reliable, and suitable for the most demanding applications in high humidity environments, and even resistant to short-term complete flooding.

The module has two analog inputs (0 – 2.5 V), an SDI12 interface, or two digital inputs, allowing the customer to connect additional equipment to the module. The module also has a simple relay input, for example, to send a signal about system tampering. Thus, when using the SDI12 interface, we can send data from 10 independent devices!

Connected sensors are optionally supplied with sensors powered by 12 V, 5 V, or 3.7 V from the GSM-2 module.