ta Logging with Network-Independent Systems

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

Mains-powered monitoring of measurement systems does not develop 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 key challenge. The following problems are faced by operators and planners:

• Risk of vandalism
• Lack of power supply
• Poor accessibility of measurement points
• Transmission of measurement data
• Handling of the increasing volumes of measurement data
• Personnel needed for commissioning and operation of facilities
• Optical/structural standards such as in landscape conservation areas

Planning Criteria

Power Supply

The first question to clear when planning a measurement place without power supply is the question of alternative power sources. In the meantime, a number of options are available on the market that range from wind power stations through fuel cells to solar cells. However, such an approach usually turns out to be impracticable because of disproportionate effort and high costs. The goal 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 variety of systems are available on the market that has been optimized for minimum energy consumption, but in this case, the complete system must be considered, where the interaction of sensors and transmitter is extremely crucial. Connecting radar sensors, for instance, which need measurement times of up to 30 seconds to an energy-optimized transmitter is not greatly effective. Hence, it makes sense to use customized ultrasonic sensors that feature a measurement time of just three seconds. Contrary to using standard sensors, this leads to 10 times extended lifetime.

Protection Against Vandalism

While the risk of vandalism cannot be fully eliminated, there are ways to lower the risk of being a potential target. It is frequently recommended to use measurement systems which cover all the components needed for signal evaluation, data transmission, data storage, sensor supply, 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 significantly 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 used 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" definitely 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 frequently protected against external forces and hence they are not extremely 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 effortless installation as well as to minimize the risk potential, the solar cell housing is combined with all the required components (for example, buffer batteries, charging control, measurement signal evaluation, etc.). As a result, the necessary 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 increasing number of measurement points often reveals main discrepancies. Furthermore, being on site in order to read out data from the measurement points needs a major investment of time and effort. Another vital drawback of this method is that real-time data is 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 via GPRS (General Packet Radio Service as service within GSM networks) has been established as a transmission method. All common GSM network providers offer this service. A GPRS modem should be incorporated in the measurement system. Such modems are available in all sizes and types for all kinds of applications. A measurement system with a 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 obtain benefits from GPRS services, a telecommunications contract has to be concluded with the selected network provider specifying billing and various other requirements. Following which, the network provider offers 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 important questions such as:

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

In a number of cases, research, organization, planning, comparison of costs, and handling of all administrative efforts exceed 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 needed. The SIM modules are strongly installed on the electronics board of the measurement unit. Due to this, it is possible to prevent oxidation of SIM card contacts and the accompanying communication failures. Being an integral part of the devices, the SIM modules are offered as units. This means, there is only one contact person for operators who no longer have to jump between the network provider and device manufacturer in case of requests.

A key advantage is being independent from a specific 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. Furthermore, this method offers the highest availability since in the event of network failure or overload, the system will automatically switch to the next available network.

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

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

At the start of the contractual period, the costs are paid as a one-off payment. For instance, a vital 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 using 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 day-to-day business. However, a number of plant operators find it complicated to set the parameters for remote data transmission via GPRS. In addition to technical barriers, there is always a fear that there would be high transmission fees in case of faulty settings, which frequently exceed the purchasing costs of the unit many times over. In standard systems, the SIM card and transmitter had to be accustomed to each other which can be accomplished by setting the transmitter with provider-specific parameters. Additional equipment, software tools and thus appropriate expertise are needed for this. During the commissioning of measurement systems for settings, tests, and the quest for the right parameters (for example, APN, PIN, 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 required. The benefits reveal specifically in case of failures since the units can be effortlessly replaced even by staff without knowledge or programming skills on the according SIM card settings.

Economic Efficiency Analysis

Typically, only the purchasing costs are taken into account when it comes to selecting a measurement data logging system; however, it is vital for operators to have an overview on the overall system costs (Total Cost of Ownership) covering the whole lifetime. The following graph presents an example of the most vital cost areas.

Figure 5. Overview on total operating costs.

The purchasing costs of measurement units available with built-in SIM modules are originally higher when compared to common GPRS devices. However, given the total costs and the whole lifetime, these measurement units will offer clear cost benefits because of savings within the remaining cost areas.

Processing of Measured Data

Besides 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. A number of different systems are available on the market for these purposes. The choice has to be altered according to the operator’s requirements and existing systems. Solutions are evolving as favorites which can be set up and then operated without the need for programming skills and which also offer universal interfaces to be linked to current control systems.

Summary

In the meantime, there is a great variety of technical solutions for network-independent data logging available, but there are some important points and hurdles which need to be considered right from the start. However, the development of new complete solutions such as the development of energy-efficient measurement systems and SIM modules allow operators to look at essentials. Essential here is the reliable, economic, 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 demonstrates 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.