Advanced lithium batteries enable mass flow meters to operate maintenance-free for decades.
By Lou Adams, Tadiran Batteries
Manufacturers of high-performance mass flow meters are increasingly deploying sensor technology to make these systems more “intelligent.”
This intelligence can take many forms, from flow meters that feature automatic control valve actuation and leak detection, to data logging and SCADA functions that increase system efficiency and reliability, to enhanced management reporting functions that enhance productivity and profitability, and which enable flow meters to effectively integrate into Smart Grids and other networks.
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Intelligent flow meter design also applies to the development of power management solutions that provide decades of reliable and trouble-free performance.
Location Dictates The Power Management Solution
When flow meters are located in easily accessible locations or near an AC power source, design engineers are presented with a wide range of options in terms of power management solutions.
However, in remote applications where battery replacement is difficult and access to AC power is either impossible or impractical due to high costs, flow meters are typically powered by primary batteries.
To illustrate this point, a flow meter located in a central facility could be powered by inexpensive consumer alkaline battery or rechargeable cell due to ease of replacement, whereas a flow meter installed in a gas pipeline located in the Artic wilderness will more likely be powered by long-life lithium batteries to ensure reliable performance and to reduce long-term maintenance costs.
In rare instances, energy harvesting devices can be considered, but this technology is largely unproven and has yet to overcome inherent performance limitations such as high cost, reduced reliability and increased size.
Most energy harvesting devices also require rechargeable batteries to capture and store energy, which totally defeats the devices’ value proposition, as rechargeable batteries have inherent drawbacks such as reduced service life, higher cost, and use chemistries that are not environmentally friendly.
Lithium Batteries Are The Preferred Choice
Lithium is widely accepted as the primary choice for remote sensor applications due to its high intrinsic negative potential. Lithium is also the lightest nongaseous metal, and therefore cells based on lithium chemistry offer the highest specific energy (energy per unit weight) and energy density (energy per unit volume) of all battery chemistries.
Lithium also reacts strongly with water, so lithium electrolytes are always non-aqueous and thus less susceptible to freezing, enabling these systems to operate continuously across a wider temperature range, with certain models capable of withstanding temperatures ranging from 55º C to +125º C. Use of a non-aqueous electrolyte also results in higher internal impedance, which can be effectively controlled during the manufacturing process.
Under the broad category of primary lithium battery types, chemical systems currently in mainstream use include lithium poly carbon monoflouride (LiCF), lithium manganese dioxide (LiMNO2), lithium sulfur dioxide (LiSO2), and lithium thionyl chloride (LiSOCL2).
As Table 1 demonstrates, each lithium chemistry offers unique performance advantages and disadvantages, so design engineers must thoroughly evaluate all options. Specifying the optimal battery also involves trade-offs, so it is important for design engineers to prioritize desired product attributes to help determine the optimal solution.
Critical factors in battery selection include minimum and maximum voltage; initial, average and maximum voltage; continuous or intermittent operation (if intermittent, the size and duration of current pulses); shelf and service life; operating temperature range; and optimal physical size and shape.
Adapting Lithium Chemistry To High Current Pulse Applications
Of all the available lithium batteries chemistries, bobbin-type Li/SOCL2 cells offer the highest energy density and voltage, excellent temperature characteristics, low self-discharge rates and excellent safety characteristics. However, bobbin-type cells are not designed to handle high current pulse applications.
To address this issue, engineers at Tadiran successfully combined lithium thionyl chloride chemistry with a unique Hybrid Layer Capacitor (HLC) to create PulsesPlus™ hybrid cells, which offer all the benefits associated with standard thionyl chloride bobbin cells, including higher capacity, lower self-discharge (less than 1% per year), lower ESR (equivalent serial resistance), a broader temperature range (–40°C to +85°C), as well as the ability to deliver high current pulses up to 15 Ah. The HLC is recharged by the battery in advance of the next pulse to eliminate passivation effects.
Combining the HLC with a lithium battery also offers the potential for an end-of-life indication when 5-10% of the battery’s total capacity is still available.
Recent Case Studies
Application specific requirements often dictate the power management solution. For example, Miltel Communications, a key player in the AMR fixed network wireless systems market, utilized long-life lithium batteries when they developed SpeedRead, a system capable of providing intra-day readings of consumption patterns, equipment tampering, maximum current, flow meter operation, and other data. Miltel’s advanced fixed base network infrastructure technology has been acquired by Badger Meter for use in their Galaxy AMI metering infrastructure systems. Badger is also using Tadiran lithium batteries to power these units.
Unique to Miltel's SpeedRead system is its ability to link a single transmitter with up to four separate meters, including multi-utility data from gas, water and electric meters connected to one data collection device. By offering a single source solution across a wide spectrum of utility services, the SpeedRead system opens the door to new revenue streams and further cost savings. Miltel has also developed a fully potted meter interface unit for underground installation in water utility meter boxes that required 20-year service life with 1-watt power output. Utilization of a C-size cylindrical PulsesPlus™ battery provided the only practical solution.
In designing systems that transmit many times a day, Miltel required a battery that wouldn't compromise battery life expectancy for increased power. Extending the time between battery replacements was critical to Miltel, since longer life translates into an important marketing advantage: reduced field service for replace batteries.
In Miltel's case, conventional lithium thionyl chloride batteries did not offer the voltage or capacity to handle multiple daily data transmissions, so they selected the PulsesPlus™ hybrid lithium battery. According to Yarum Locker, President of Miltel Communications, Ltd., Tadiran's PulsesPlus battery offered "an ideal solution, allowing Miltel's systems to be smaller and more cost-efficient, with minimal service required over a ten to twenty year period."
Galaxy AMI systems utilize high-powered radio transmitters to connect to various power lines, public wireless networks and municipal Wi-Fi systems to provide water utility managers with enhanced data flow and control functionality. Other applications developed by Miltel include telemetry transmitters for agricultural data collection from sensors above ground as well as buried moisture sensors.
The same chemistry found in PulsesPlus batteries has been used to power automatic meter reading (AMR) devices for decades, for example, in 1984, Hexagram (now Aclara) began installing millions of AMR units powered by lithium thionyl chloride batteries. Today, virtually all of its initial installations continue to operate on their original batteries after a quarter century. Laboratory tests have confirmed that these 25-year-old batteries still have enough remaining capacity to offer many more years of dependable service, even under harshest environmental conditions.
Designing For Energy Conservation
Design engineers need to carefully consider energy consumption issues when designing flow meter sensors, as today’s increasingly feature-rich systems place greater demands on batteries to power such features as remote programming, cycle codes, passwords and diagnostic capabilities.
Significant design challenges revolve around the need to extend battery life. For this reason, AMR meters are typically programmed to operate in multiple modes, including a sleep or standby mode, where power consumption is nil or at a low background current; a measurement or interrogation mode, which requires a few hundred milliamps of energy; and a transmission mode that requires high current pulses for a period of seconds or longer before returning to sleep or standby status.
When a valid wake-up signal is received from an interrogation unit, the AMR flow meter can begin to communicate with the interrogating device via cellular phone, internet or RF signal. After transmitting encoder identification and meter reading data to the interrogation unit, the interrogation unit signals to the meter that valid reading parameters have been met and instructs the meter’s communication interface to power-down. This power-down mode allows the flow meter to conserve energy until the next interrogation session.
PulsesPlus™ bobbin-type lithium thionyl chloride batteries are ideally suited for this application due to its high capacity, high energy density, long life and proven reliability under extreme environmental conditions. In addition, these cells deliver the high current pulses required to maximize data streams and increase the frequency of transmissions without negatively affecting battery life.
PulsePlusTM batteries also offer the lowest self-discharge of any lithium chemistry. The self-discharge rate is governed by the cell’s electrolyte composition, its production processes, as well as mechanical considerations. Self-discharge rates can also be negatively affected by the composition of the electrolyte, as lithium batteries are not created equal in terms of the level of electrolyte impurities and/or parasitic reactions.
Extreme temperatures can also impact battery performance and life expectancy. Temperatures below -20°C can be problematic for certain battery chemistries, since cold electrolyte becomes less active, leading to higher internal impedance, which may lead to battery failure. When subjected to extremely high temperatures (above +60°C), certain battery chemistries and mechanical sealing techniques start to fail, affecting both short-term performance and long-term reliability.
Advanced lithium battery technology has been proven effective for long-term flow meter applications. However, lithium batteries are not created equal in terms of their performance and reliability based on the quality of the raw materials utilized or the quality systems utilized throughout the manufacturing process. So design engineers must perform careful due diligence throughout the battery selection process, properly vetting battery suppliers to ensure that the batteries deliver as advertised, providing the necessary capacity, energy density, safety, manufacturing process compatibility and reliability to deliver decades of trouble-free performance.
At the same time, battery manufacturers must continually respond to rapidly evolving flow meter designs by delivering long-term power management solutions, working in close partnerships with flow meter manufacturers to ensure that emerging battery technologies keep pace with rapidly improving product technology.
For more information email sales@tadiranbat.com or visit www.tadiranbat.com.