The concept of a hybrid meter reading system sounds easy enough. Design the system so that the utility has a number of choices on how the meters are read – handheld, vehicle-based, or fixed network – and let the utility mix and match these options based on the specific application. Structure the system so that all the readings channel through a single head-office system; and don’t forget that the utility doesn’t want to have to replace its MIUs if it migrates from mobile to fixed network reading.
So where do we start? First, we need to view this challenge as a system and not as a collection of components. All the pieces must fit together seamlessly, and we must bear in mind that changes to one element of the system may have impacts throughout the entire system. Secondly, we must consider how the system is optimised. Some systems are optimised for fixed network or mobile applications, and we must be sure this hybrid system is optimised for both reading methods.
Now we’re ready to look at some of the specific design trade-offs that we should consider. In doing so, we must keep in mind that because this is a system, all these design decisions are interrelated.
Communication paths: 1-way, 1½-way or 2-way. In a 1-way system, the MIU transmits a reading at a predetermined interval. In a 1½-way or 2-way system, the MIU remains in an idle mode until it receives a wake-up signal. This means that the MIU is constantly drawing a low level of power as it ‘listens’ for the signal. 1½-way or 2-way systems depend on two separate communications to achieve a successful reading – first the MIU must receive the wake-up signal, and secondly the collection device must receive the transmitted meter reading. These MIUs may also be susceptible to reduced battery life due to inadvertent wake-up signals.
Unlicensed or Licensed Frequency: Many 1½-way systems use a licensed broadcast wake-up signal but transmit their readings in an unlicensed band (set of frequencies). It is important to consider the pros and cons of both the licensed wake-up signal and also the typically unlicensed transmission signal when considering the system.
Narrow-band or Spread-spectrum: Narrow-band systems are those that operate on a single frequency, similar to a garage-door opener. These systems are generally easier to design and use less expensive components because the transmission frequency is fixed. However, if noise or other interference is present, the read success rate may be greatly diminished. Furthermore, since all the MIUs are transmitting on this single frequency the chance of collision is increased, which further reduces the read success rate.
Spread-spectrum systems, whether frequency-hopping or direct sequence, are capable of transmitting meter readings at a higher output power and over a broader frequency range. Spread-spectrum systems are therefore able to reduce the impact of interference and collisions by simply moving to another frequency within the band. As a result, spread-spectrum is generally more reliable than narrow-band systems.
Power Transmission Interval: How often should we transmit the reading? This really only applies to 1-way systems, since 1½-way and 2-way systems wake up the MIU. If the MIU doesn’t transmit often enough, the read success rate or reading efficiency of a mobile application will suffer. If the MIU transmits too often, the chance of collision in a fixed network mode may increase. And don’t forget the battery life – if the MIU transmits too often, battery life may be compromised.
Reading redundancy: In a mobile application the receiver is usually moving, so there are multiple opportunities for the communication to occur. For example, a chain link fence may block one transmission, but as the mobile receiver moves down the street the next transmission may have a clear communication path. In a fixed network the receivers are stationary, so they must be positioned to provide for reading path redundancy to increase the read success rate.
Range: In order for a system to operate effectively in a fixed network mode, there is a certain minimum range required between the MIU and the data collection device. If the range is not adequate, more concentrators are required and the economics of the fixed network system may not be viable. In considering range, we’ll focus on MIU output power and receiver sensitivity. A simple analogy is that of a normal conversation. Whether or not the message is heard depends a great deal on the clarity and volume of the speaker (transmitter) and the hearing ability of the listener (receiver). Other factors such as RF modulation and topography affect range, but output power and receiver sensitivity usually have the greatest impact.
MIU Output Power: On the surface, it might seem that the greater the output power the better. However, while a certain minimum output power is needed to generate sufficient range, an MIU generating too much output power may result in increased collisions and reduced battery life. Collisions can become a real issue when the MIUs use a narrow-band transmission and as the MIU transmits more often.
Receiver Sensitivity: Hand in hand with the MIU output power, we must consider the sensitivity of the receiver. Receivers can be designed with enhanced sensitivity or reception ability, which increases the effective range of the system. However, a good receiver must also be able to filter noise and handle high concentrations of transmitters.
Battery Life: Generally, the utility market expects a battery to last 10 to 15 years. As noted above, many of the key design decisions will impact battery life. Additionally, the efficiency of the design of the power supply circuitry of the MIU will contribute to battery life.
Neptune optimised its ARB® Water Revenue System™ with a full understanding of these trade-offs. In addition, Neptune developed its hybrid RF approach around some fundamental principles that ensure the system provides value to the utility:
- System Integrity – The system must offer the utility the best value for a wide variety of applications and allow the utility to migrate up the technology pyramid.
- Data Integrity – The data must be accurate and reliable from the absolute encoder all the way to the utility host computer.
- Measurement Integrity – The data is only as accurate as the measurement device, so the meter must meet the highest standards of accuracy and reliability.
- Supplier Integrity – The supplier must stand behind its system with the highest level of customer support, such as Neptune’s certification by the Software Support Professionals’ Association.
ARB WATER REVENUE SYSTEM DESCRIPTION
In Neptune’s second generation of the R900 RF MIU, the power output, transmission interval, MIU power supply and battery technology have been optimised to operate in both mobile and fixed network modes. Like its predecessor, the second generation R900 is designed to operate as a 1-way transmitter, using frequency-hopping spread-spectrum in the unlicensed 902 to 928 MHz band, and is compatible with all Neptune handhelds and mobile systems. The second generation R900 has maintained many other unique features, including compatibility with multiple encoders which eliminates the need for programming the MIU, durability for harsh applications, and ease of installation.
The EZNet System rounds out Neptune’s hybrid system. EZNet is a fixed network system for targeted commercial and industrial applications. The EZNet System is designed to be deployed as a stand-alone system or operated in conjunction with Neptune’s handheld and/or mobile data collection systems as a hybrid automated data collection solution.
The EZNet host software is Windows-based and easy to use. It is designed to interface with EZRouteMAPS meter reading software applications, facilitating hybrid system architectures and system migration. The EZNet software also incorporates a flexible interface to CIS/Billing systems.
With careful evaluation of the design decisions, hybrid systems are feasible and can offer the greatest flexibility and value to the utility.