There has been a need for autonomously operating measuring systems for quite some time, but until now they have only been implemented using locally read data-loggers. This meant that the data that was acquired was never up-to-date and merely provided an historical picture since the measuring devices did not have a continuous function monitoring facility.
The use of mobile radio networks and the Internet has now made it possible to create a virtual combination of widely distributed measuring systems in one location and make use of the acquired data in real-time.
Modern measuring systems are cost-effective
Professional measuring technology has reaped considerable benefits from the use of components and technology originally developed for the large volume consumer markets. A current example is the use of mobile radio networks for data transmission. GSM reception coverage is extensive and the price of telephone modules and call costs low enough that it can be used as a cheap and simple measurement acquisition method platform.
The cost of data transmission is a fraction of the cost of personnel for measurement acquisition. Furthermore, the measuring system including GSM transmission is only slightly more expensive than the equivalent data-logger without GSM capability. The cost of transmitting measured data via e-mail is extremely cheap at the moment; if a prepaid card is used, there are not even any monthly charges.
Data transmission via e-mail or SMS is the easiest solution to implement in practice, because not much needs to be done at the receiving end. A standard mobile phone is sufficient for SMS transactions or a PC with an Internet connection for e-mail.
Data processing: the PC as a data-logger
The heart of such a measuring system is the user-friendly and free GSM-2 Data Manager software. It collects the data, monitors and controls the different measuring stations (GSM-2) and is used to display or automatically process the data, which is stored in a MySQL database.
The data that is transmitted by the GSM-2 (e-mail/SMS) is continuously read by the Data Manager and stored in the database, making it evident at a glance whether all measuring stations are operating correctly. In the event of an error, eg, missing data, this is shown on the PC screen or the responsible person is notified by SMS or e-mail. Measured data can be displayed in graphical format and the measuring station locations displayed on a map. Configuration changes for the individual measuring stations (GSM-2) are made on the PC. The new configuration is transmitted by e-mail and received by the relevant GSM-2 module.
Applications
The GSM-2 is suitable for use in locations where no power supply is available or cables cannot be used. Typical applications are tanks on vehicles or building sites and ground and waste water level measurements.
GSM-2 for groundwater level measurement
The monitoring of groundwater levels or the surface levels of lakes and rivers is geographically a wide-ranging task. It is carried out by different state-run institutions and also private water and energy providers.
Keller, therefore developed the GSM-2 module for its water level measuring sensors to meet this market need. Measurements like this are usually performed manually. However, the measurement frequency is extremely dependent on the accessibility of the measuring points and the prevailing weather conditions. In order to equip the existing measuring stations with a measuring system, the GSM-2 module has been designed with a diameter that allows it to be inserted into the existing sounding pipes.
The measuring stations, most of which are located in remote areas for geographical or hydrographic reasons, usually do not have a power connection. In other words, a battery- operated system with as long a service life as possible is required. However, the list of requirements gets longer: the measuring equipment must be resistant to water and humidity and also be able to withstand short periods of immersion. Finally, it must be protected against theft and vandalism.
Quick and easy installation
The entire GSM-2 measuring module is simply inserted into the sounding pipe and secured by the level sealing cap. No complicated and 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 Data Manager, which automatically starts to manage the new measuring station immediately.
The electronics and the battery of the GSM-2 module are accommodated in a sealed stainless steel housing with an external diameter of 48 mm. Depending on the ambient conditions and the configuration, the battery-operated device can have a service life of more than 10 years. The GSM module is simply switched on when it is needed i.e. in order to call up incoming configurations or send the measuring data or the system configuration.
Several level values that have been measured within a defined time period and stored are sent in a single message – e-mail or SMS. At the same time, critical events such as rapid level changes and levels that exceed maximum or minimum limits can be detected and additional messages transmitted. The periodic transmission of system information containing battery capacity, antenna signal strength and other information also takes place periodically.
Measuring inputs for various sensors and applications
In addition to the RS-485 interface, via which the pressure or water level can be measured with accuracy using Keller water level sensors, an air pressure and temperature sensor is installed in the module itself. This makes it possible to make water level measurements using the so-called AA measuring method (absolute-absolute). The advantage of this is that no humidity-sensitive capillary tube needs to be installed in the cable of the level sensor. This makes the measuring station extremely robust and suitable for reliable use in damp and wet environments; not even short periods of immersion cause the measuring station to fail.
The two voltage inputs (0–2,5 V), the SDI12 interface or the two digital inputs allow users to connect applications with different kinds of sensors to the device. From a simple switch contact (digital input) to an expensive and complex water analysis unit with up to 10 parameters (SDI12 interface).
The connected sensors are optionally supplied with a voltage of 12, 5 or 3,7 V by the GSM-2.
For more information contact Instrotech, 27 (0)11 462 1920, [email protected], www.instrotech.co.za
| Tel: | +27 10 595 1831 |
| Email: | [email protected] |
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