Micro-machined Silicon Pressure Transducers

Omegadyne announces the most durable version of its high accuracy MM Series micro-machined silicon pressure transducers. The new hermetically sealed version of the MM Series features all welded Stainless Steel construction, 316 wetted parts and glass to metal seals (GMS) at the electrical outlets. This ensures that the unit is hermetically sealed from external environments and the media. Designed for use on automotive and aircraft test platforms and anywhere environmental concerns demand the most durable characteristics. 

The sealed MMA500V Series has a micro machined silicon core that provides high accuracy, low drift and excellent long term stability in the harshest environments. Ranges from 100 psi to 5000 psi, accuracies from 0.08% to 0.03% and a variety of pressure and electrical connections make this MMA500V Series Transducer extremely versatile. The temperature compensation range can be as broad as -40 to 200*F (-40 to 104*C) and thermal errors as low as +/- 0.3% over the compensated range. Operating temperature range is -49 to 250*C (-45 to 121*C). The MMA500V Series design is further ruggedized with a secondary containment system in the event of diaphragm rupture. A 5-Point NIST traceable calibration certificate included.

The MM Series pressure transducers offer “Custom Designed” features with fast delivery. Our modular design allows you to construct a pressure sensor to meet your application requirements, with guaranteed fast delivery… typically from stock to 2 weeks. Our product configurator found online at omegadyne.com allows quick and easy configuration of a transducer that meets the exact needs of your project.

www.omegadyne.com

ifm efector Introduces New 3D Image Sensor

EXTON, PA – ifm efector inc. introduces a new 3D Image Sensor for object evaluation. The compact sensor uses time-of-flight distance measurement to identify the height of any object in the field of view. An integrated 64 x 48 pixel array – in which each pixel represents a time of flight measurement – defines the field of view for the sensor. 

This technology provides critical information in applications such as palletzing and de-palletizing, material handling, bulk level of materials and intelligent routing/sorting. With a list price of $1450 (U.S.), ifm states that the 3D Image Sensor is a new benchmark for price / performance in reliable 3D object detection. 

3D Image Sensor Uses Photonic Mixing Device (PMD) Principle Based on Time of Flight Measurement
The Photonic Mixing Device (PMD) principle is based on Time of Flight (TOF) distance measurement. In its most simple version, a light pulse is radiated from the sensor. This pulse is reflected by an object and detected by the sensor’s smart pixel receiver element. A comparison between the optical and electrical reference signals yields an output signal that carries the desired distance information.

Time of Flight (TOF) distance measurement is not new to the market. The challenge is that traditional TOF components use a photodiode for a receiver element and require additional external electronics for signal acquisition and processing. These type of components are used to detect only one measurement and are costly due to the response time required for Time of Flight measurement. Using these existing TOF components to achieve 3D imaging can be expensive for industrial markets.

In comparison, ifm’s 3D image sensor’s receiver element is a System-on-Chip design. The complete sensor element and electronics are built on a 0.25 mm square silicon chip. This miniature chip enables 3D imaging using Time of Flight, reduces the size of the sensor and its cost.

For image capture, the 3D sensor’s 64 x 48 pixel array projects 3072 points of reference, capturing the entire image in three dimensions. Each pixel within the array has two gates that are controlled by an oscillator that oscillates at a frequency of 20MHz. Light is emitted from the sensor and reflected by the target and received back into the PMD chip (also connected to the oscillator). The electrons are converted into photons and are separated into the optically sensitive area of the semiconductor called the “moble charge carrier”. This built-in functionality means that the sensor can pre-process the signal, removing the need for expensive high-speed electronics. Relating the phase difference measured by each pixel to the speed of light gives the distance travelled by light falling onto the detector. The phase shift of the light is then compared to the reference signal and sent from the chip as the representative distance for that pixel. Information from all the pixels is then brought together to create a 3D image.

The sensor also includes patented Suppression of Background Illumination (SBI). This technology allows the sensor to eliminate the effects of external lighting such as sunlight and internal high-powered lighting. This allows the sensor to be used in almost any indoor or outdoor application.

Multidimensional Measurement for Industrial Automation Applications

Palletizing and de-palletzing 

The 3D image sensor solves a variety of application challenges for the material handling industry. The challenge in this process is detecting when a layer of product is complete or incomplete. If a stray box is left on the top layer of a pallet, and the box goes undetected, there’s a risk that the robotic arm will crush the product or the missing product will create an unbalanced load on top of the pallet. The 3D image sensor can be mounted to the top of a palletizer. The sensor‘s 64 x 48 pixel array projects 3072 data points of reference onto a pallet. The 3D image sensor evaluates the entire layer of a pallet and sends the information back to the main control indicating the highest or lowest point regardless of where it is in its point of view.

Material handling in airport logistics
In airports across the country, airport logistics moves thousands of pieces of luggage every day. Determining the gross dimension and volume of a piece of luggage before it reaches the inspection scanner is crucial to proper luggage flow. If a bag is determined to be too large, it can be removed before it reaches the scanner. To pre-determine baggage size, many airports are required to use multiple high-cost sensors to measure all sides of the luggage to determine height, width and depth which adds cost and complexity.

The ifm 3D image sensor uses a standard algorithm to determine the gross volume of a piece of luggage in its field of view. The PMD sensor’s pixel array sends 3072 data points to detect the luggage size and volume. The sensor sends a signal to the main control indicating when a luggage piece is too large to fit through the scanner. The luggage can then be removed before it reaches the scanner and maintain proper luggage flow.

Bulk material level applications
Detecting the level of materials in a bin or hopper is necessary to run a machine at maximum efficiency. An empty or “run dry” condition can cause machine downtime, place stress on equipment, and risk damage to components. In traditional level applications, multiple single-point position sensors are placed above a hopper or bin to detect the level of the material inside. Fine materials such as grain and sand, and bulk products such as plastic bottles and pellets, can shift within the hopper creating hills and valleys. Single-point sensors detect one spot in the material. Any hills or valleys in the material will provide multiple level readings that can lead to an incorrect level detection. The efector 3D image sensor is mounted above a hopper or bin. The sensor’s pixel array of 3072 data points spreads across the grain to detect the entire area. The high and low points are identified, providing accurate level monitoring and total volume.

Robust, compact design for industrial application
The solid-state, robust metal housing measures only 42 x 62 x 42 mm and is designed to withstand harsh environments and to perform in fast-moving applications. Application parameters are quickly established with the sensor’s Setup Wizard software that can be used with a PC. The Setup Wizard guides the user in a few steps to configure the application. The sensor can provide either digital or analog outputs.

www.ifmefector.com

Eaton Introduces View Series™ Photoelectric Sensors

PITTSBURGH, PA - Eaton Corporation announces it is introducing the View Series™ of photoelectric sensors, comprised of the new IntelliViewTM and NanoViewTM product families. The View Series sensors expands Eaton’s photoelectric sensor capabilities with new models designed for a variety of challenging industrial applications. The IntelliView sensors are a family of compact, high-performance specialty photoelectric sensors aimed at the needs of packaging, material handling, and other machinery original equipment manufacturers (OEMs). The NanoView sensors are a family of sub-miniature rectangular photoelectric sensors designed for applications and industries where optical performance is important but smaller, less expensive sensors are required.

Models in the IntelliView product family detect grayscale, color and ultraviolet (UV) luminescent registration marks on product and packaging labels. Background and foreground suppression models allow for precision sensing over extended ranges to meet the needs of a wide variety of machinery OEM applications. Other models are capable of reliably measuring a target’s distance and providing an analog output to a control system.

The IntelliView family features:

Foreground/background suppression sensors that are field-adjustable, with ranges from 2.4 inches to 3.9 feet.

Distance sensors able to identify the target’s location within the sensing field to a high degree of accuracy.

Color sensors that reliably detect different color tones and grayscale tints, and can be taught to recognize up to three colors independently.

Contrast (colormark) sensors that can distinguish two surfaces according to the contrast produced by the difference in reflection.

UV luminescence sensors that detect fluorescent or phosphorous materials, even against reflective backgrounds like glass, mirrored or ceramic surfaces.

Available in industry-standard compact rectangular or flat-tubular packages with M12 micro connectors.

Canadian Underwriters Laboratories (cUL) listed and Conformité Européenne (CE) approved, ready for global application.

The View Series of sensors also includes the NanoView family. These sub-miniature sensors are well suited for applications in packaging, material handling, food and beverage, and pharmaceutical industries where space is limited. Despite their small size, NanoView sensors are robust, powerful, highly reliable, and fit advanced optical performance into a tiny package.

The Nanoview family includes:

A comprehensive family, including an 8.2 foot polarized reflex; a 13 inch diffuse; a 4 inch
fixed-focus diffuse; a 20 foot thru-beam; and a 2.6 foot clear object detector.

A package size that is less than 1.5 inches long and half an inch deep.

Available with M8 connectors or 6.5 foot cable.

C-UL listed and CE approved.

The NanoView family also includes specialty sensors capable of solving difficult application challenges. These include a fixed-focus diffuse sensor, able to accurately sense targets with precision at its rated focal point of 3.9 inches; a clear object detector model capable of sensing clear objects such as plastic or glass bottles, films, sheets, and packing materials; and thru-beam mode sensors with a narrow beam option, able to detect small targets with high accuracy.

www.eaton.com

Web-Enabled Ultrasonic Sensors

LOGAN, UT – Automation Products Group, Inc. (APG) introduces LOE Web-Enabled Ultrasonic Level Sensors. These self-contained ultrasonic sensors provide a low-cost, tailored sensing solution for monitoring liquids or solids in remote tanks, and can also be used for local tank monitoring applications.

LOE ultrasonic sensors feature Power Over Ethernet (POE) for easy wiring, AutoSense software for hassle-free operation, and can be easily programmed and configured remotely – without requiring any configuration software – via APG’s levelandflow.com website, and locally via the sensor’s embedded web page. Sensor level data is transmitted to a dedicated website that utilizes an open-source MySQL database format to ensure user data is available in any format that might be required of the application.

Three models are available. The LOE-2126 provides a detection range of 1 to 25 ft., the LOE-3136 provides a detection range of 1.5 to 40 ft., and the LOE-6126 provides a detection range of 4 in. to 180 in. The LOE-6126 delivers a best-in-class blanking distance of just 1 in., compared to 4 in. for most other competitive sensors, which uniquely enables a single sensor to monitor the entire tank or vessel range.

Sensor readings are uploaded to a database via a standard Ethernet (TCP/IP) connection, where the level or volume information can be viewed from any computer with internet access, via a password-protected web page. The sensor and/or the web-server can be user-programmed to trigger the website to send an email, text message or both when a predetermined level or volume is reached. These sensors also feature two internal relays that can be programmed to control pumps or activate local alarms.

Sensor parameters and settings can be changed at any time via the sensor’s internal web page, which is readily accessible by simply entering the sensor’s IP address into any internet browser on any computer connected to the same network. The internal web page also displays the level or volume information, effectively turning any computer on the network into a potential remote tank display/monitor.

www.apgsensors.com

TURCK’s PT4400 Pressure Sensor Series

Minneapolis, MN — TURCK introduces its new PT4400 pressure snsor series designed for intrinsically safe locations. This series utilizes a media isolated stainless steel diaphragm for use in pneumatics, water management, hydrogen storage, hydraulic systems, oil and gas, HVAC/R and industrial OEM equipment. 

The PT4400 is rated for UL/cUL 913 (CSA 157) Class I, Division 1, Groups C and D when installed with an approved barrier, such as a TURCK IM33 module. Constructed without welds or o-rings, these sensors allow exceptional pressure ranges up to 10,000 psi and burst pressure ranges up to 20,000 psi.

PT4400 sensors are manufactured using MEMS (microelectromechanical systems) technology. With its one-piece sensing design, the PT4400 offers many advantages over other pressure sensing technologies, including a high life cycle, plus high overload and burst pressure cycles.

www.turck.us

Compact 3100 Series Pressure Transducer

Setra Systems, Inc. offers its Compact 3100 Series pressure transducer providing a low cost solution for OEM applications such as Hydraulic Controls, HVAC Systems, Engine Controls, Industrial Process, Off-Highway Equipment, Compressors, and Pumps. 

This unit’s small footprint, less than 1 inch in diameter, makes it ideal for installations where space is at a premium, and its all stainless steel construction is resistant to corrosive media typically found in industrial process applications.

The 3100 Series employs highly accurate thin film technology and a unique custom designed ASIC offering exceptional performance with accuracy to 0.25% full scale, long-term stability of 0.1%/yr, and thermal stability accurate to within 1.0%/100°F over the entire compensated temperature range of -40°F to 250°F.

Offered in pressure ranges from 100 psi up to 30,000 psi and a wide variety of outputs(0 to 5, 1 to 5, 0.5 to 4.5, 1 to 6 , 0 to 10 VDC, 4 to 20 mA, and 0.5 to 4.5 V ratiometric,), pressure fittings (NPT, UNF, BSP and Metric), and electrical connectors (M12, Packard, Deutsch, DIN43650C and others), this unit can be configured in any number of ways without incurring extra costs associated with customization. In addition, voltage units are available with a dual temperature/pressure output.

www.setra.com

An Alternative to Vision Systems: A Touch Screen Image Sensor

by Brent Evanger, Banner Engineering, Sr. Application Engineer—Vision Sensors 

When an inspection application requires more sophisticated data acquisition than that provided by a traditional photoelectric sensor, many application engineers will choose a vision system. Through it, they can obtain image-based data and identify label orientation, part presence and arrangement, and other features. But for some of these applications, a full vision system may not be required. Instead, you can use a compact touch screen image sensor with no PC or additional electronics required.

Label Orientation: The touch screen image sensor lets you set inspection parameters on the spot, and then examine a target object, such as a salad dressing bottle, to verify label placement and orientation.

A touch screen image sensor can combine the capabilities of three separate sensors into one housing. One sensor is a match sensor. It compares the target object to a stored reference point, identifying parts of irregular shape, alphanumeric characters, etchings and labels at rapid production speeds. An area sensor identifies target features within a region of interest, ideal for detecting drilled holes on a metallic component or inspecting blister packs, and verifies that all 
features are correctly sized and located. The third sensor has a similar purpose—examining an area for specific features—but offers tools that adjust for motion. 

Drilled Hole Inspection: The image sensor features integrated lighting to create contrast between target features (drilled holes) and their background (metal plates), allowing any reject parts to be readily identified.

These tools allow the sensor to detect objects of varying position and orientation on the production line. The image sensor also incorporates integrated lighting and adjustable lenses to optimize image contrast, as well as accommodate changing plant conditions.

Injection Molding Verification: Once the sensor is programmed, it compares the obtained image—in this case, a plastic container—to a reference pattern, confirming its size and shape match the parameters set. If the target object fails this inspection, it is rejected from the production line.  

The sensor’s touch screen LCD display is used for setting up an inspection and modifying parameters. Once you select the sensor type (match, area, or area with motion), it captures a sample image. From this point, you configure the sensor by adjusting the region of interest, setting inspection parameters, and designating the minimum and maximum pass count. The final setup configuration and logged inspection results can be downloaded from the sensor to a USB drive through the sensor’s USB port. To minimize system downtime, you can set new application parameters offline through the sensor’s software emulator, and then upload these new configurations onto the sensor using the USB drive.

Banner Engineering
www.bannerengineering.com

EtherCAT Sensors Can Receive Power Over Standard Cat 5 Cables

The EK1132 Power over EtherCAT junction terminal enables EtherCAT® sensors to receive power over a standard Cat 5 cable. Ultra high speed EtherCAT sensors that deliver low microsecond (µs) level communication can now be more easily installed in industrial applications. Based on the IEEE standard 802.3af, the EK1132 requires only a standard EtherCAT/Ethernet cable for the fieldbus signal and the power supply.

The EK1132 EtherCAT junction suits shaft encoders or length measuring devices that can now be connected by a single cable. The sensor supply voltage of 48 V is generated in the EK1132 junction from the 24 V used as the industry standard. The maximum current input of the terminal devices is 350 mA. The signal and energy transfer takes place on the same wire so four-wire cables can be used. The sensors are connected to Power over EtherCAT via a 4-pin connector such as M12. The maximum possible Ethernet cable length is 100 m.

An intelligent power distribution system detects which power consumer belongs to which performance class and distributes the total available power (15.4 W) to the connected devices accordingly.

Beckhoff Automation
www.beckhoffautomation.com

Designing with Thermistors

John R. Gyorki, Editorial Director 

Temperature sensor applications usually fall into one of three general categories; monitoring, control, or circuit compensation, and four sensor types; thermocouples, thermistors, resistance-temperature detectors (RTD), and semiconductor temperature sensors. When selecting a sensor, some key characteristics to consider include temperature range, accuracy, response time, minimal temperature effect on the measured object, and the type of signal conditioning required.  Other factors are long-term stability, mechanical ruggedness, and cost. 

Unleaded NTC thermistor discs are frequently used in numerous automobile engine sensors to measure air and coolant temperature. The discs are located inside the tip of the housing, usually under a spring-load to maintain contact pressure. 

The table compares thermistor characteristics with other types of temperature sensors and shows that thermistor devices are essentially passive variable resistors and require excitation current to produce an output signal. In other words, you cannot just connect a voltmeter across the leads of a thermistor, touch the sensor to a hot object, and expect to see a voltage.   

Thermistors have a considerably higher sensitivity than most other sensors, but they are also much less linear. Although special high-temperature sensors, such as chromium oxide ceramic thermistors made by GE Sensing can operate up to 1000^oC, conventional devices have a relatively narrow temperature range and are not an optimal choice when long-term accuracy is required. However, thermistors are usually less expensive than the other sensors and react faster to temperature changes.

All sensors require linearization, but each to a different degree. Also, to achieve high accuracy the circuit must be calibrated with the actual thermistor sensor connected. These two tasks can be accomplished with analog conditioners and calibration circuits, but they can be quite complex and require manual calibration. If a digital design is used instead, the sensor signal is digitized by an analog-to-digital converter (ADC) and the linearization and calibration are done in software with 
minimum operator involvement.

Thermistor Fundamentals    
Thermistors are solid-state, temperature-sensitive resistors that come in two types: negative temperature coefficient (NTC) and positive temperature coefficient (PTC). As the names imply, the resistance of an NTC thermistor is inversely proportional to temperature, whereas the resistance of a PTC thermistor is directly proportional. The sensors’ terminal resistance changes with the temperature change of the thermistor body, which can come from ambient heat, self-heating due to excitation current, or both.

PTC thermistors are used most often for circuit-overload protection, compared to NTC devices that are used primarily for temperature measurement and compensation. This article focuses on temperature measurement devices, so only NTC thermistors are discussed.  

The resistance of an NTC thermistor decreases with an increase in its body temperature, however, the rate of resistance change is not linear. It is greatest at the lower temperature limit and gradually diminishes as the temperature increases.

NTC thermistors are a sintered mixture of metallic oxides, which include nickel, cobalt, manganese, and sometimes other oxides. The elements are formed as beads, chips, discs, rods, or thin-films. Bead thermistors are drops of semiconductor paste deposited on two platinum alloy wires, sintered at a high temperature. The wires are then cut to make individual thermistors. Chip and disc thermistors are fabricated as a thin sheet of material (wafer), and sintered at high temperature. The sides are silvered for attaching leads, and the wafers are cut into discs or chips. Rod thermistors are simply extruded.

Thermistor elements can be glass encapsulated, epoxy coated, or remain uncoated (bare). Bare thermistors respond faster, are smaller, and cost less, but they have no provisions for protection from the environment and mechanical impact. An epoxy coating can protect the device from the environment, but it slightly slows the response time and increases the cost.  Glass encapsulation ensures a hermetic seal, high-voltage insulation, and resistance to corrosive atmospheres. Long-term stability of glass encapsulated parts is typically ten times better than the stability of epoxy coated parts.

Mounting features include unleaded discs that require spring-loaded contacts, silver or gold electrodes for wire bonding, and surface mounting provisions such as those for SMD chips.  The leads can be axial or radial, bare or insulated, and straight or kinked. Axial lead and SMD parts are intended for automatic PCB insertion and pick-and-place equipment. Radial-lead devices and unleaded discs are well suited for temperature probe assemblies.

An unleaded NTC disc thermistor (a.) is commonly found in temperature probes. Adding radial leads to an uncoated disc thermistor (b.) lets it mount on a printed circuit board. Coating the disc thermistor with epoxy (c.) protects it from the environment. Epoxy-coated chip thermistors with flexible insulated leads are ideal for installations with limited space.
(Photos courtesy of GE Sensing & Inspection Technologies, Billerica, MA.)

One special type, thin-film thermistors, are deposited on a ceramic or flexible Kapton® base, only several tens of thousands of an inch thick. They have low dissipation values and fast reaction times due to their small mass. For example, TF series of thin-film NTC thermistors from Selco Products Company, are suitable for a -50^oC to +90^oC temperature range and have a dissipation value of 0.7 mW/^oC with a thermal time constant of 2 s, both in still air. They are ideal for air and other gas temperature measurements as well as probe assemblies.

Accuracy ratings vary greatly between different devices, depending on the application. For example, general-purpose disc thermistors typically have tolerances that range from ± 20% to ± 2%, and interchangeable thermistors can have accuracies as high as ± 0.05^oC in a narrow temperature range. They are available for probe replacement without system recalibration. For example, U.S. Sensor’s PR103J2 ultra-precision, interchangeable 10-kΩ thermistor is a highly accurate and stable sensor that matches the J-type NTC thermistor’s R-T curve with ± 0.05^oC accuracy from 0^oC to 50^oC. Other resistance values from 2 kΩ to 50 kΩ are also available.

Several thermistor-related terms that are listed in catalogs and data sheets can help you select parts:
• The zero-power resistance, R_o, is a dc resistance specified at a particular temperature and an excitation current so small that the self-heating produced by power dissipation can be neglected. This special temperature is called the Standard Reference Temperature, and is typically 25^oC. 
• The resistance ratio characteristic is a ratio of zero-power resistance measurements made at two specific temperatures. It is typically the ratio of resistance at 25^oC to the resistance at 125^oC.
• The thermal time constant, τ, is the time in seconds required for a thermistor that dissipates zero power to change its body temperature 63.2% of the total temperature change in response to a step-function change in ambient temperature. This parameter characterizes the speed with which a thermistor can react to fast temperature changes and helps compare the response time of different devices. 
• The dissipation constant, δ, is a ratio of the change in thermistor power dissipation to the change of thermistor body temperature. It is measured in mW/ ^oC and is specified at a certain temperature. Both τ and δ depend strongly on the measured object or media.  For example, the dissipation constant of a GE type DC95 interchangeable chip thermistor is 8 mW/^oC in stirred oil, but is only 1 mW/^oC in still air. The thermal time constant is 1 second in stirred oil, but is ten times longer in still air.
• The maximum power rating is another characteristic related to power dissipation. It is the maximum power in mW at an ambient temperature of 25^oC that a thermistor can dissipate for an extended period of time without degrading its characteristics. This rating must be derated based on the ambient temperature.
• The zero-power temperature coefficient of resistance (TCR), α, is the ratio of the rate of change of zero-power resistance at any temperature point, T, to the zero-power resistance at that point: 

α_T = 1/R_T (dR_T)/(dT)

Where:
α_T = temperature coefficient of resistance at temperature T, 
Ω / Ω / ^oC, or %/ ^oC
R_T = resistance at temperature T, Ω
dR_T = change of resistance, Ω
dT = change of temperature, oC

Another way to express the temperature coefficient is:

α_T = – B/T²

Where:

B = material constant, ^oK
T = temperature, ^oK

Unfortunately, thermistor temperature coefficients are highly non-linear over their operating range, which means that the coefficient itself varies somewhat with temperature. A coefficient is at its highest value at its lowest temperature limit and gradually decreases as temperature increases. One value of a particular coefficient might work for a narrow temperature range, but most often, thermistor measurement circuits must be linearized to cover large temperature swings.

By simply adding one resistor in series with the thermistor, the output voltage vs. temperature curve can be linearized. When resistance vs. temperature linearization is desired, the resistor should be connected in parallel with the thermistor.

Circuits for linearizing thermistor outputs can be comprised of series, parallel, and series-parallel combinations of fixed resistors and additional thermistors. The simplest circuit is a parallel resistor, the value of which can be calculated from the following equation:

R = [R_TM(R_TL + R_TH) – 2R_TLR_TH] / [R_TL + R_TH – 2R_TM]

Where:

R = value of parallel resistor, Ω
R_TL = thermistor resistance at the lowest temperature T_L, ?
R_TH = thermistor resistance at the highest temperature T_H, Ω
R_TM = thermistor resistance at the midpoint temperature T_M, Ω 
Midpoint temperature TM = (TL + TH) / 2, °C

Simple on/off temperature control circuits and applications with a narrow temperature range and relaxed accuracy requirements usually do not need linearization. A simple Wheatstone bridge circuit is usually quite adequate. Another example that does not require hardware linearization is a digital temperature circuit where the linearization is handled in software. 

A simple on/off temperature control circuit can be designed using a thermistor in one leg of a Wheatstone bridge. Resistors R1, R2, and R3 must have a low temperature coefficient and be exactly matched to guarantee accuracy.

Operating Conditions
Certain operating conditions can significantly lower measurement accuracy or reliability and should be avoided. For instance, self-heating might become a hidden accuracy error. Thermistors generate their own heat when their excitation current is too high. The power it develops from the excitation current and its own resistance (P = I²R) can noticeably elevate the temperature of the thermistor body above the environment. Parts with a large dissipation constant, d, a low thermal resistance mounting, and other means of superior heat dissipation will have a lower temperature rise. But the primary way to avoid excessive self-heating is to keep the excitation current as low as possible.

Most measurement errors and premature failures often come from careless installation and operation. For example, although thermistors are considered to be rugged devices, take care not to crack a case, separate a bond, or exceed the upper temperature limit.

Lastly, aging is a phenomenon that is often overlooked and if not considered in the maintenance schedule, can lead to loss of calibration accuracy after extended periods of use. It manifests as an effective thermistor terminal resistance drift over time due to slowly changing resistances in the bulk material and in the contact areas between the leads and the thermistor material. 

For more information: 
Contact John Gyorki at the Engineering Exchange, 
www.engineeringexchange.com

www.omega.com
www.gesensing.com
industrial.panasonic.com
www.murata.com
www.ussensor.com
www.vishay.com
www.selcoproducts.com
www.thermosensors.com
www.jumoplus.com

Navigation Sensor Expands Use of AGVs

Automated guided vehicles (AGVs) typically work in climate controlled environments, although you will find rugged versions working out doors. A laser navigation sensor, the LS5 Navigator, promises to expand AGV application. It handles indoor and outdoor environments as well as cold storage, paving the way for AGVs to operate in harbor, loading platform, and similar applications.

The sensor withstands wide variations in temperature (-30° C to +50° C) and relative humidity (< 95%) as well as mechanical stress like vibrations and shocks. A direct drive motor with few moving parts minimizes maintenance.

The optics system maximizes measurement and consistency. It is adaptable to different types of communication, simplifying sensor replacement. It also works with AutoSurveyor, a software tool for automatic and accurate determination of reflector coordinates.

LS5 Navigator is available in two versions: One for outdoor/indoor use and one for indoor use only.

www.DanaherMotion.com

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