Network–Independent Data Logging

With growing awareness for the ecologic and economic use of resources and a high number of legal provisions which, among other demands, need to fully prove the efficiency of water protection measures and special constructions, a highly dense measurement data network is indeed required. In addition, the demands for early-warning systems for the monitoring of rivers, groundwater levels and flood protection facilities are growing. In order to make full use of all choices of action the recorded measurement data must be immediately and reliably available.

Mains-powered monitoring of measurement systems does not create any issues in wastewater systems with current infrastructure and can be performed by using common components. However, operating measurement systems in non-urban areas is a major challenge. The following problems are faced by planners and operators:

• lack of power supply
• poor accessibility of measurement points
• risk of vandalism
• transmission of measurement data
• personnel needed for commissioning and operation of facilities
• optical/structural standards such as in landscape conservation areas
• handling of the increasing volumes of measurement data

Planning Criteria

Power Supply

The first question to clear when planning a measurement place without power supply is the question of alternative power sources. Meanwhile, many options are available on the market that range from wind power stations through solar cells to fuel cells. However, such an approach generally turns out to be impracticable because of disproportionate effort and high costs. The aim is to operate the preferred measurement systems with built-in rechargeable or standard batteries in the long run with the lowest possible maintenance requirements.

In the interim, a range of systems are available on the market that has been optimized for minimum energy consumption, but in this case, the complete system must be taken into account, where the interaction of sensors and transmitter is very crucial. Connecting radar sensors, for example, which need measurement times of up to 30 seconds to an energy-optimized transmitter is not highly effective. Hence, it makes sense to use customized ultrasonic sensors that feature a measurement time of just 3 seconds. Contrary to using traditional sensors, this leads to 10 times longer lifetime.

Protection Against Vandalism

While the risk of vandalism cannot be eliminated fully, there are ways to reduce the risk of being a potential target. It is often recommended to employ measurement systems which cover all the components needed for signal evaluation, sensor supply, data transmission, data storage, and energy supply in a single, compact enclosure. The higher space requirements as well as the use of more than one enclosure and the appropriate wiring considerably increase the risk potential. The drawing shown below is one example of a measurement system with directly connected sensors and all the desired components being enclosed in a single enclosure.

If the appropriate measurement system is selected, it is seldom necessary to support the rechargeable batteries employed with additional solar cells. In this case, the formula "the more energy-efficient the measurement system, the smaller the solar cells needed and the smaller the risk of theft" certainly applies.

Figure 1. Example of a measurement system with data transmission via GPRS and built-in rechargeable battery.

In consumer solar systems, the glass surfaces are not often protected against external forces and hence they are not very robust. Meanwhile, solar systems specifically meant for measurement data recording in non-urban areas and featuring IP 68 protection in robust, impact-proof die-cast enclosures are available with the solar cell being further protected through armored glass. For easy installation as well as to minimize the risk potential, the solar cell housing is integrated with all the required components (e.g. buffer batteries, charging control, measurement signal evaluation, etc.). As a result, the required sensors can be directly connected to the solar module, as shown in Figure 2.

Figure 2. Example of a robust solar-powered system with data transmission via GPRS.

Transmission of Measurement Data

During the planning stage, the lack of infrastructure at the measurement point raises the question of how to transmit the measurement data. A shortage of staff combined with the growing number of measurement points often reveals major discrepancies. Moreover, being on site in order to read out data from the measurement points needs significant investment of effort and time. Another major drawback of this method is that real time data are never available which can be applied for planning purposes or to sufficiently respond to specific events. Only historic data sets can be used for such evaluations.

For some time before, the transmission of measurement data through GPRS (General Packet Radio Service as service within GSM networks) has been established as a transmission method. All common GSM network providers provide this service. A GPRS modem should be integrated in the measurement system. Such modems are available in all types and sizes for all kinds of applications. A measurement system with built-in modem is suited for use with network-independent data recording, as this prevents cross wiring.

Figure 3. Modem with SIM card slot.

Figure 4. Complete system with integrated modem and plugged SIM card.

To avail of GPRS services, a telecommunications contract has to be concluded with the selected network provider specifying billing and other needs. Following which, the network provider provides a SIM card which should be plugged into the measurement unit. An appropriate SIM card slot is provided in common GPRS modems.

The required agreement presents operators with significant questions such as:

• Which network is available on the measurement point?
• Which provider is best?
• How can I manage the telecommunications contracts?
• What is the expected data volume and what are the costs?
• How can I manage the required SI M cards?
• How can I avoid cost explosion?
• How can I handle the running costs within the cost plan?
• How can I deal with recurrent payment flows?

In many cases, research, planning, organization, comparison of costs, and handling of all administrative efforts go beyond the limits of the true measurement task such as simple level measurement.

Contrary to standard modems, innovative solutions are available, and thanks to using the so-called SIM modules SIM cards are no longer required. The SIM modules are firmly installed on the electronics board of the measurement unit. As a result, oxidation of SIM card contacts and the accompanying communication failures can be prevented. Being an integral part of the devices, the SIM modules are provided as units. This means, there is only one contact person for operators who no longer have to jump between network provider and device manufacturer in case of requests.

A major advantage is being independent from a certain network provider. The system will log in using the most powerful GSM network available at the measurement place. As a result, it is no longer necessary to look for available network providers from one measurement place to another. In addition, this method provides the highest availability because in the event of network failure or overload, the system will automatically switch to the next available network.

The use of SIM modules allows for the use of GPRS services without having to conclude a telecommunications contract and because of this it is no longer necessary to look for an appropriate network provider, to compare services, to survey contractual deadlines, etc.

When it comes to selecting an appropriate provider, one of the most important basics for decision-making is absolute cost control regarding transmission fees. If SIM modules are used, billing models and fixed prices are available that are similar to pre-paid solutions. Based on the predicted utilization, these models use data packages that contain all costs covering a specific period. In such cases, it is not significant for operators which service provider has been selected by the SIM module at the measurement place.

At the beginning of the contractual period, the costs are paid as a one-off payment. For example, an important benefit in case of being used together with government-subsidized projects is that the purchasing costs alone are subsidized and not the operational costs. With this pre-paid solution, the running transmission costs can be transferred into the purchasing costs and monthly payments can also be saved as it is the standard with common telecommunications contracts. Since this method is employing the same principle anywhere in the world, it can be used without any issues even in close vicinity to country borders.

Commissioning of Measurement Systems with Data Transmission via GPRS

Meanwhile, wiring electric connections and measurement sensors is a part of daily business. However, many plant operators find it difficult to set the parameters for remote data transmission through GPRS. Besides technical barriers, there is always a fear that there would be high transmission fees in case of faulty settings, which often exceed the purchasing costs of the unit many times over. In standard systems, the SIM card and transmitter had to be adjusted to each other which can be accomplished by setting the transmitter with provider-specific parameters. Additional equipment, software tools and thus appropriate expertise are required for this. During the commissioning of measurement systems for settings, tests and the quest for the right parameters (e.g. PIN, APN, etc.), normally one or two working hours need to be scheduled.

Connect sensors – plug battery – done!

Using measurement systems with built-in SIM modules is as simple as it sounds as no more settings are needed. The benefits reveal specifically in case of failures because the units can be easily replaced even by staff without knowledge or programming skills on the according SIM card settings.

Economic Efficiency Analysis

Usually, only the purchasing costs are considered when it comes to selecting a measurement data logging system; however, it is important for operators to have an overview on the overall system costs (Total Cost of Ownership) covering the entire lifetime. The following graph shows an example of the most significant cost areas.

Figure 5. Overview on total operating costs.

The purchasing costs of measurement units featuring built-in SIM modules are initially higher when compared to common GPRS devices. However, given the entire lifetime and the total costs, these measurement units will provide clear cost benefits due to savings within the remaining cost areas.

Processing of Measured Data

In addition to selecting the best possible measurement system for network-independent data logging, the processing of measured data represents the next pillar for the conception of the complete system. Many different systems are available on the market for these purposes. The choice has to be adjusted to the operator’s requirements and existing systems. Solutions are evolving as favorites which can be set up and operated without the necessity for programming skills and which also provide universal interfaces to be linked to existing control systems.

Summary

Meanwhile there is a great variety of technical solutions for network-independent data logging available, but there are some hurdles and important points which need to be considered right from the start. However, the emergence of new complete solutions such as the development of energy-efficient measurement systems and SIM modules enable operators to look at essentials. Essential here is the economic, reliable and ecologic facility operation rather than the administration of telecommunications contracts or investing a lot of manpower. When selecting an appropriate network-independent measurement system, it shows that the initially cheapest solution is not essentially the most cost-efficient solution.

This information has been sourced, reviewed and adapted from materials provided by NIVUS GmbH.

For more information on this source, please visit NIVUS GmbH.