GSM-based autonomous measuring system

Paul Boughton

Marcel Gautschi reports on an advanced measuring system that features remote data transmission.

The use of mobile radio networks and the internet has made it possible to create a virtual combination of widely distributed measuring systems in one location, and make use of the acquired data on the spot.
The GSM reception coverage is so far advanced and the prices of telephone modules, prepaid cards and mobile data transmission are so low that the present solution represents the cheapest and simplest measurement acquisition method, not just for decentralised or extremely remote measuring points, but also easily accessed locations. The savings associated with reduction in personnel costs are particularly striking. 
The receive end benefits too, because the measuring data can be read out conveniently at the computer receiving the data via mobile phone (SMS) or directly via e-mail/FTP.

The heart of the measuring system is the user-friendly and free GSM-2 DataManager Windows software. It collects the measuring data, monitors and controls the different measuring stations and is used to display or automatically process the measuring data stored in a MySQL database. The data that is transmitted by the GSM-2 is continuously read in by the DataManager and stored in the database. This makes it possible to establish at a glance whether all measuring stations are operating correctly.

The monitoring of groundwater levels or the surface levels of lakes and rivers is a widespread task. 
In order to continue using the existing measuring stations, the GSM-2 module has been designed with a diameter that allows it to be inserted directly into the so-called sounding pipes.

The entire GSM-2 measuring module is simply inserted into the 2-inch diameter sounding pipe and secured by the level sealing cap. No complicated or expensive installation of antenna with mast and solar panel is required. After installation, the GSM-2 transmits its configuration with measuring station name and position to the DataManager, which automatically starts to manage the new measuring station immediately. The GSM-2 is also available as a box in various versions, such as with explosion protection, and as an OEM module.
In addition to the RS485 interface, which delivers highly accurate pressure or water level measurements in conjunction with KELLER level sensors, the GSM-2 module also features an air pressure and temperature sensor. This makes it possible to take water level measurements using the so-called AA (absolute-absolute) measuring method. Another advantage is that no humidity-sensitive capillary tube is required in the cable of the level sensor. This means the measuring station is designed for reliable use in damp environments and not even short periods of immersion cause it to fail. The two voltage inputs (0 – 2.5 V), the SDI12 interface and the two digital inputs support the use of all kinds of sensors, from a simple switch contact (digital input) to a complex water analysis unit with up to 10 parameters (SDI12 interface). The GSM-2 supplies the connected sensors with either 12.5 or 3.9 volts.

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Marcel Gautschi is with Keller in Winterthur, Switzerland. 

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