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Powering remote flow meters: advanced lithium batteries enable mass flow meters to operate maintenance-free for decades.

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.

Intelligent flow meter design also applies to the development of power management solutions that provide decades of reliable and trouble-free performance.

The Location Dictates

When flow meters are located in easily accessible locations or near an AC power source, design engineers are presented with a 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.

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.

Primary 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 (from 55[degrees]C to I25[degrees]C).

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).

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.

* Shelf and service life.

* Operating temperature range.

* Optimal physical size and shape.


Of all the available ]ithium 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 higher capacity, lower self-discharge (less than 1 percent/year), lower equivalent serial resistance, a broader temperature range (-40[degrees]C to 85[degrees]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-I0% of the battery's total capacity is still available.

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 ate typically programmed to operate in multiple modes (sleep/standby, measurement/interrogation, transmission).

When a wake-up signal is received from an interrogation unit, the AMR flow meter can begin to communicate with the interrogating device. After transmitting encoder identification and meter reading data to the interrogation unit, it instructs the meter's communication interface to power-down--allowing the flow meter to conserve energy until the next interrogation session.
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Title Annotation:New Products: Hydraulics & Pneumatics
Author:Adams, Lou
Publication:Product Design & Development
Date:Jun 1, 2009
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