Field-Effect Sensors Eliminate Pump Switch Failure: Residential Applications

Executive Summary

Field-Effect sensing has the unique ability to detect fluids and semi-solid materials without making direct contact. If the material being targeted is conductive in nature, and the barrier wall through which is being is non-conductive, then Field-Effect is the technology of choice. Field-Effect sensing technology is ideally suited for sump, lift station, underground vault, wet well and storm water fluid level management applications.

Since 1997, nearly 200 million Field-Effect sensors have been deployed in industries such as appliance, consumer, automotive, medical and fitness (e.g., liquid level sensing, or in touch activated machine controls). By 2005, Field-Effect sensors had become the de facto standard for fluid level detection in marine and recreational vehicle applications, such as holding tank level monitoring and bilge pump control systems.

Over the years, pump life has been limited to the durability of a single component, the mechanical contact switch. As switch technology progressed from non-integrated to integrated float and switch designs, improved manufacturing processes, advanced coatings, etc, pump durability continued to be governed by the limitations of the mechanical contact switch and associated moving parts.

Recent advancements in solid-state electronic design have enabled a generation of more reliable pump controls. Durability issues surrounding the mechanical contact switches were eliminated with the use of solid-state transistors to manage high current switching. Although this was a considerable improvement in itself, the remaining question was how to reliably detect changes in liquid level without the use of moving floats, or without making direct electrical contact with the fluid?

Non-contact sensing technology was considered to be the answer, and even though there were several technical solutions available in the marketplace (capacitive, ultrasonic, and optical), only capacitive has proven to be a practical and cost effective for residential sump pump applications. The limitation of capacitive is that it's prone to false actuations and pump run-on attributed to the varying mineral content of the water being managed and the associated scum build up on the sensors themselves as the water level fluctuates. In addition, capacitive technology has required complex software algorithms to establish an environmental baseline for switching, which is a challenge in itself. The solution to these obstacles proved to be non-contact, s Field-Effect sensing technology coupled with solid-state switching components.

Engineers and plumbing professionals should consider Field-Effect a "best in class" solution when evaluating fluid level detection technologies. The benefit of a five (5) year warranty with solid state Field-Effect control makes it an economical choice for facilities management professionals. No longer is the pump switch the limiting factor in an organizations scheduled maintenance activities.

Economic Background for Residential Applications

With more than 10% of all residential structures that have full or partial basements reporting leakage from outside the structure through the basement (American Housing Survey for the United States: 2007, U.S. Department of Commerce, September 2008, Table 2-7, p. 62), the proper operation of the sump pump system for homeowners is imperative. The consequences of switch failure for residential sump pumps and their industrial equivalents extend far beyond the cost of repair.

Homeowners have always been faced with the potential cost and inconvenience of restoration of basements, but, in addition, the U.S. Environmental Protection Agency (EPA) has identified mold as an environmental pollutant that diminishes indoor air quality (IAQ). The mitigation of molds caused by indoor moisture has become a public health issue that is now reflected in the home inspection process.

Homeowners and operators of public buildings now face risks in the longer term for reporting and/or filing claims for water damage. Faced with large increases in claims for water damage, the insurance industry has established a database, known as the Comprehensive Loss Underwriting Exchange (CLUE), to facilitate the exchange of information among insurers to drop or deny coverage based on a home's history of claims or damage reports. The proper functioning of pumps and their switches is paramount to maintaining public health and to preserving the value of residential and commercial structures for their owners.

Homeowners, installers, and other industry professionals can also take advantage of the added cost savings opportunity of purchasing a less expensive pump which does not include the switch function as part of the offering. These pumps are typically priced at the low end of the commercial spectrum, even though mechanically, they're the same sump pump being offered in the high-end systems with integrated switch capability. This retail savings can range anywhere from $15.00 to $80.00 depending on the pump model and retail outlet selected.

Technical Overview

Field-Effect sensors are digital, solid-state electronic devices that can detect conductive materials or liquids such as water or the human touch. The sensor's cell design uses an integrated circuit (IC) that switches its output state when the conductive target is sensed. A Field-Effect cell is comprised of three main elements, the IC, a unique sensing electrode geometry, and two resistors. Moreover, Field-Effect requires no moving parts, floats, software, or any other mechanism to make its sensing decision.

When 5 VDC is supplied to the sensor, a low power electric field is created. The field emanates directly through any protective dielectric barrier such as plastic or glass that may surround or cover the sensor. When a conductive object or material enters the field, the sensor detects the change and indicates an event has occurred with a corresponding output signal. The input stimulus to the field is typically water in most liquid level sensing applications, as is the case in TouchSensor's? LevelGuard Home Sump Pump Control product line.

The performance advantages of Field-Effect sensors in plumbing applications include:

Solid-state electronic designwith no moving parts or electrical contacts to wear out, bind, or become contaminated by fluids. All electronics are encased in rugged plastic and are completely isolated.
Fail-safe recognition from Underwriters Laboratories(UL File# - E187820)
Six (6) year replacement warrantywith an optional four (4) year extended warranty in fluid sensing applications. Field-Effect fluid detection sensors have been tested to over 1.5 million operational cycles without failure.
Operating temperature range of -40°C to 120°C. Accelerated life testing of Field-Effect sensors (cycling temperature between 0°C and 105°C and relative humidity between 40% and 85%) has confirmed an operational life of more than 20 years without failure.
Immunity to contaminants. The low impedance nature of the Field-Effect sensor design, combined with proprietary electrode geometry, make the Field-Effect sensor highly resistant to the effects of surface contaminants and mineral buildup.

Summary

The importance of reliability in fluid detection systems has increased over time. Under pressure to cost-reduce their products while improving system performance, manufacturers (and their vendors) have cautiously introduced innovations through their channels of distribution. Engineers and plumbing professionals now have the ability to specify a fluid level control system that meets and/or exceeds the performance needs of their system designs and client expectations.

In 2004, TouchSensor impressed the Marine & RV Industry when it introduced the SensaSwitch 20, the world's first and only solid-state electronic submersible bilge pump control using Field Effect fluid sensing technology. In 2005, TouchSensor again broke new ground with the launch of the next generation SensaSwitch Ultra...the world's first and only CE rated, 2-wire, 12 and 24 VDC - 20 Amp Marine bilge pump switch. TouchSensor's success continues today, as several of the world's leading OE bilge pump manufactures have embraced the performance benefits of Field-Effect by directly integrating the technology into their products. LevelGuard is the culmination of the right technology meeting a specific customer need. Change the Spec to Field-Effect!

About TouchSensor? Technologies, a wholly-owned subsidiary of Methode Electronics: TouchSensor engineers and manufactures Field-Effect sensors for appliance, exercise equipment, medical, and automotive markets. Since 1997, TouchSensor has delivered more than 200 million Field-Effect cells for use in the markets it serves. Visit http://www.TouchSensor.com to learn more.

About LevelGuard?:LevelGuard? introduces Field-Effect technology for fluid level detection to the residential, commercial, industrial and municipal plumbing markets. Please visit www.LevelGuardproducts.com/sump to learn more and subscribe to our email newsletter for technical updates.

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Machine Olfaction Device (MOD) Sensors (Part Two)

Conducting Polymer Sensors

A polymer is basically a substance made up of many repeating chemical units (or molecules). Conducting polymers, as the name indicates, are conjugated polymers, organic compounds that have an extended p-orbital system, through which electrons can freely move from one end of the polymer to the other. The most common are polyaniline (PAni) and polypyrrole (PPY) [13]. A conducting polymer film is usually used as a sensor to detect vapours/odours using the same principles as those applicable for MOS*.

Polymers can be used for many devices combining unique optical, electrical, and mechanical properties. Conducting polymers can be used for optical effects and underlying physical processes.

Conjugated polymers e.g. poly(para-phenylene, polyaniline, and poly(p-phenylenevinylene) characterized by high flexibility

Most conducting polymers can be made to transfer electrons to other materials such as Buckminsterfullerene(Carbon 60 "C60 Buckyball") [13].

Both inorganic and organic materials can be used to create LEDs (light-emitting diodes), such as InGaN (Indium Gallium Nitride) materials or cadmium selenide nanocrystals, where the physical process involves quantum-wells.

Conducting polymers are made by 'electro polymerisation' of complex organic dyes specifically derivatives of the substances polypyrole, polyaniline and polythiophene.

Depending on the exact chemical structure of the polymer, each one can be given a different conductive behaviour. In this way, a list (or database library) can be built of different types of conducting polymer (i.e. sensors) with each one testing a different type of molecular.

a. Polymer Preparation

Conducting polymer sensors are made by chemical or electrochemical polarization from monomers: "aniline, pyrolle".

The addition of dopants (any kind of conductive materials) increases the polymer conductivity as they create an accumulation of positive or negative particles, e.g. self-doped polyaniline [13].

b. Sensing Mechanism

When the analyte interacts with the sensing surface (i.e. when a molecule in the sensor interacts with another molecule in the environment) the resulting output is a detectable signal [14]. This is the basic principle of the chemical sensor.

All polymers, in general, have a similar detecting mechanism. Chemical sensors based on conjugated polymers detect a variety of analytes and have the ability to detect these at low concentrations, this is because they contain a "Chromophore", a chmical group contained within the polymer where the energy for the excitation of an electron is very low [14].

When contact is made with analyte molecules, the conductivity of the "polymer" changes. A current will be created within the sensor in proportion to the concentration of the analyte.

The next step is that the generated current will usually be detected by the signal processing circuits in the MOD. A pattern will then be generated indicating the type of element/molecules in the sample.

c. Advantages of polymer sensors

1- They work within a wide range of operating conditions (e.g. variations in average

room temperature, pressure and humidity).

2- Functional groups that interact with different classes of odorant molecules can be

built into the active material, providing a high level of sensitivities and selectivity.

3- Organic materials tend to be easier to use than inorganic oxides, as they can be

used close to ambient environmental conditions than, for example, MMOS. Also,

they are more easily modified to react with specific gaseous species than inorganic

materials.

d. Disadvantages of polymer sensors

1 - Even though polymers can be made highly sensitive (point 2 above), organic

materials in general are usually poor conductors, and hence measurement

conductivity can be difficult.

2 - Can be thermally unstable.

3 - Can be sensitive to water.

* MOS = Metal Oxide Semiconductor.

Najib Altawell

References

[13] MacDiarmid A. G.,"Polyaniline and polypyrrolw: where are we headed?"Synthetic Metals 84 (1997) 27 -34

[14] Zhou Q. and Swager T. M. "Fluorescent Chemosensors Based on Energy Migration in Conjugated Polymers: The Molecular Wire Approach to Increased Sensitivity" J. Am. Chem. Soc. 1995, 117, 12593-12602

[15] Vaefolomeev S. (1999) "Conducting Polymer Sensors"

ASTEQ Technologies for sensors 1999

[16] Finklea, H. O., lecture notes (1998 ) "Gas Phase Sensors"

Department of Chemistry West Virginia University, Morgantown, WV 26506-6045

© Altawell 2008

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Humidity Analyzers And Temperature Sensors Explained

Humidity analyzers, also popularly referred to as moisture sensors or hygrometers, together with temperature sensors are technical gadgets that not only play an important role in various and diverse manufacturing and industrial processes but also are incorporated in many ordinary home appliances we probably have at home.

Humidity Sensors

In industrial and manufacturing environments, moisture sensors are highly sophisticated technical gadgets that enable factory operators as well as industry managers make sure that the product being produced is being manufactured within acceptable levels of humidity. Industries need to comply with high industry quality standards and hygrometers help them in this task. From the human and pet food industry to chemical and pharmaceutical labs, to the wood and leather industry, these devices have multiple uses. For instance, they are useful to determine if the potato chips are packed crispy, if the breakfast cereal will be crunchy and tasty when we eat it every morning and that the chemical compounds used to prepare a certain medicine have not lost their healing properties as result of being exposed to a too dry or wet environment.

In industrial environments there isd usually more than one moisture analyzer set up to monitor the humidity content of the product being manufactured as the acceptable range may vary from step to step of the manufacturing process. In order to make sure that the product complies with the quality standards, a sample is taken and weighed. Then it is introduced in the moisture analyzer and dried. Once dried it is weighed again. The difference between the two weights tell the operator if the environment is dry enough or if further changes need to be made.

As regards home appliances, the air conditioner has a moisture sensor that helps the device know when the air conditioned room has reached the desire level of dryness. Whenever it starts getting humid again, the hygrometer automatically triggers the air conditioner again. Many clothes dryers also come with hygrometers and they help women make sure that their clothes are dried efficiently without being over exposed to dryness.

Antique shops also have moisture analyzers as they are useful to protect relics and antiques from the devastating effect of humidity.

Temperature Sensors Temperature sensors are also more popularly known as thermometers. In clothes dryers they are very helpful as they can be used to make sure that the delicate clothes fibers are not exposed to overheat unnecessarily.

Eduard Jim written for Temperature Sensors.

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