How to Develop and Qualify Sensors for Arctic Conditions

The climatic conditions in the arctic are characterized by cold winters and short summers. There is a large variability in climate and weather: Some regions face permafrost and are ice covered year-round with temperatures down to -40°C / -40°F (and lower), other land areas face the extremes of solar radiation up to +30°C / +86°F in summer.

As oil and gas exploration, as well as renewable energy (e.g. cold climate versions of wind turbines) move into arctic areas, the need grows for sensors designed to deal with the extreme conditions and to perform reliably over their whole life cycle.

One option is the implementation of a Highly Accelerated Life Test (abbreviation HALT) in the development process. The basic idea of HALT is the accelerated aging of electronic products (including sealing gaskets, potting compound, housing etc.) with the aim of detecting their possible weak spots as early as possible and to correct them at the development stage.

Example of a sensor in the HALT test facility (Balluff magnetostrictive linear position sensor BTL)

The item under test is subjected to higher and higher thermal and mechanical stress in order to cause failures. The limits where the product will fail functionally or be destroyed are determined in order to push these limits as far out as possible, and so achieve a higher reliability for the product.

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Product operational specs = data sheet values

The HALT procedure – in brief:

a) Analysis of weaknesses already known, definition of failure criteria, establishing the stress factors

b) Stressing the test specimen beyond the specification to find the “upper and lower operating limits”, and the “upper and lower destruct limit” for temperature, rapid change of temperature, vibration, combined vibration and temperature stress

c) Determination of the causes of failure

d) Devising a solution to eliminate the weaknesses

e) Repeating of steps b) to c)

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Example: Temperature step test – cold and hot
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Example: Combined vibration test and rapid temperature changes
Cowan
Example: Cowan Dynamics E2H Electro-Hydraulic valve actuator Photo: Cowan Dynamics (Canada)

In contrast to other environmental tests, HALT is not qualification testing according to specific technical standards (as  ISO/IEC etc.), but it applies stimuli to the items under test until they fail, so weak spots will be revealed. A HALT test is not an exam you can pass!

However, if sensors are implemented into more complex automation systems that will be operated in remote areas, this method may help to prevent major faults in the field and is therefore also used in the aircraft and automotive industry.

For more information about Balluff testing methods and the laboratory, please visit www.balluff.com or download our brochure “The Balluff Testing Laboratory”.

 

Non-Contact Infrared Temperature Sensors with IO-Link – Enabler for Industry 4.0

Automation in Steel-Plants

Modern production requires a very high level of automation. One big benefit of fully automated plants and processes is the reduction of faults and mishaps that may lead to highly expensive downtime. In large steel plants there are hundreds of red hot steel slabs moving around, being processed, milled and manufactured into various products such as wires, coils and bars. Keeping track of these objects is of utmost importance to ensure a smooth and cost efficient production. A blockage or damage of a production line usually leads to an unexpected downtime and it takes hours to be rectified and restart the process.

To meet the challenges of the manufacturing processes in modern steel plants you need to control and monitor automatically material flows. This applies especially the path of the workpieces through the plant (as components of the product to be manufactured) and will be placed also at locations with limited access or hazardous areas within the factory.

Detection of Hot Metal

Standard sensors such as inductive or photoelectric devices cannot be used near red hot objects as they either would be damaged by the heat or would be overloaded with the tremendous infrared radiation emitted by the object. However, there is a sensing principle that uses this infrared radiation to detect the hot object and even gives a clue about its temperature.

Non-contact infrared thermometers meet the requirements and are successfully used in this kind of application. (The basics of this technology were discussed in a previous post.) They can be mounted away from the hot object so they are not destroyed by the heat, yet they capture the Infrared emitted as this radiation travels virtually unlimited. Moreover, the wavelength and intensity of the radiation can be evaluated to allow for a pretty accurate temperature reading of the object. Still there are certain parameters to be set or taught to make the device work correctly. As many of these infrared thermometers are placed in hazardous or inaccessible places, a parametrization or adjustment directly at the device is often difficult or even impossible. Therefore, an intelligent interface is required both to monitor and read out data generated by the sensor and – even more important – to download parameters and other data to the sensor.

Technical basics of Infrared Hot-Metal-Detectors

Traditional photoelectric sensors generate a signal and receive in most cases a reflection of this signal. Contrary to this, an infrared sensor does not emit any signal. The physical basics of an infrared sensor is to detect infrared radiation which is emitted by any object.
Each body, with a temperature above absolute zero (-273.15°C or −459.67 °F) emits an
electromagnetic radiation from its surface, which is proportional to its intrinsic
temperature. This radiation is called temperature or heat radiation.

By use of different technologies, such as photodiodes or thermopiles, this radiation can be detected and measured over a long distance.

Key Advantages of Infrared Thermometry

This non-contact, optical-based measuring method offers various advantages over thermometers with direct contact:

  • Reactionless measurement, i.e. the measured object remains unaffected, making it possible to measure the temperature of very small parts
  • Very fast measuring frequence
  • Measurement over long distances is possible, measuring device can be located outside the hazardous area
  • Very hot temperatures can be measured
  • Object detection of very hot parts: pyrometers can be used for object detection of very hot parts where conventional optical sensors are limited by the high infrared radiation
  • Measurement of moving objects is possible
  • No wear at the measuring point
  • Non-hazardous measurement of electrically live parts

IO-Link for smarter sensors

IO-Link as sensor interface has been established for nearly all sensor types in the past 10 years. It is a standardized uniform interface for sensors and actuators irrespective of their complexity. They provide consistent communication between devices and the control system/HMI.  It also allows for a dynamic change of sensor parameters by the controller or the operator on the HMI thus reducing downtimes for product changeovers. If a device needs to be replaced there is automatic parameter reassignment as soon as the new device has been installed and connected. This too reduces manual intervention and prevents incorrect settings. No special device-proprietary software is needed and wiring is easy, using three wire standard cables without any need for shielding.

Therefore, IO-Link is the ideal interface for a non-contact temperature sensor.

All values and data generated within the temperature sensor can be uploaded to the control system and can be used for condition monitoring and preventive maintenance purposes. As steel plants need to know in-process data to maintain a constant high quality of their products, sensors that provide more data than just a binary signal will generate extra benefit for a reliable, smooth production in the Industry 4.0 realm.

To learn more about this technology visit www.balluff.com.

Hydraulic Cylinder Position Feedback, Revisited

In a previous Sensortech post entitled “Hydraulic Cylinder Position Feedback“, we discussed the basic concept of hydraulic cylinder position feedback.  In case you might have missed that post, here it is for an encore appearance.

Magnetostrictive linear position transducers are commonly used in conjunction with hydraulic cylinders to provide continuous, absolute position feedback.  Non-contact magnetostrictive technology assures dependable, trouble-free operation.  The brief video below illustrates how magnetostrictive position sensors are used with hydraulic cylinders.

Continue reading “Hydraulic Cylinder Position Feedback, Revisited”

What’s best for integrating Poka-yoke or Mistake Proofing sensors?

Teams considering poka-yoke or mistake proofing applications typically contact us with a problem in hand.  “Can you help us detect this problem?”

We spend a lot of time:

  • talking about the product and the mistakes being made
  • identifying the error and how to contain it
  • and attempting to select the best sensing technology to solve the application.

However this can sometimes be the easy part of the project.  Many times a great sensor solution is identified but the proper controls inputs are not available or the control architecture doesn’t support analog inputs or network connections.  The amount of time and dollar investments to integrate the sensor solution dramatically increases and sometimes the best poka-yoke solutions go un-implemented!”

“Sometimes the best poka-yoke solutions go un-implemented!”

Many of our customers are finding that the best controls architecture for their continuous improvement processes involves the use of IO-Link integrated with their existing architectures.  It can be very quickly integrated into the existing controls and has a wide variety of technologies available.  Both of these factors make it the best for integrating Poka-yoke or Mistake Proofing due to the great flexibility and easy integration.

Download this whitepaper and read about how a continuous improvement technician installed and integrated an error-proofing sensor in 20 minutes!

Flexible Cables Don’t Flex For Long

Recently I read an article in Machine Design called “When Flexible Cables Doesn’t Flex for Long” by Leland Teschler which talks about different aspects of flexible cable terms, causes of breakage and testing.

The article touches on different lingo between flexible, high-flex and high-flex-life. Flexible and high-flex mean the same thing.  Google’s definition of flexible is the capability of bending easily without breaking. High-flex-life is described by Northwire as a cable designed to survive 10 million to 20 million flexing cycles. Those are just the common terms used to describe flexing of a cable, but there are manufacturers that use their own flexing name to describe their cables.

Teschler also describes the feel of a cable, whether the cable bends easily or not, based on different degrees of limpness or stiffness. “All in all, cable makers say the stiffness or limpness of the cable has nothing to do with its flex life.” The article goes on to describe a limp cable as a jacket that is made from soft materials, or finely stranded conductors, that allow the cable to move easily but is not meant to be used in applications with repeated flexing.

ULTestSetupThe last part of the article mentions how cables are tested for flexing. There is not a standard in the industry so different manufacturers can use differernt tests. The 3 most common tests are twist and flex test, tick-tock cable test, and UL test setup. Teschler pointed out the main focus for UL and CSA is to test for fire safety and UL test the cables for runs of 15,000 cycles.

Overall, I really enjoyed the article and highly suggest giving it a read to understand more about raw cable and testing requirements.

To see Balluff’s offering of UL listed cables click here.

When is a Weld Field Immune Sensor Needed?

When the topic of welding comes up we know that our application is going to be more challenging for sensor selection. Today’s weld cells typically found in tier 1 and tier 2 automotive plants are known to have hostile environments that the standard sensor cannot withstand and can fail regularly. There are many sensor offerings that are designed for welding including special features like Weld Field Immune Circuitry, High Temperature Weld Spatter Coatings and SteelFace Housings.

For this SENSORTECH topic I would like to review Weld Field Immune (WFI) sensors. Many welding application areas can generate strong magnetic fields. When this magnetic field is present a typical standard sensor cannot tolerate the magnetic field and is subject to intermittent behavior that can cause unnecessary downtime by providing a false signal when there is no target present. WFI sensors have special filtering properties with robust circuitry that will enable them to withstand the influence of strong magnetic fields.

WFIWFI sensors are typically needed at the weld gun side of the welding procedure when MIG welding is performed. This location is subject to Arc Blow that can cause a strong magnetic field at the weld wire tip location. This is the hottest location in the weld cell and typically there is an Inductive Sensor located at the end of this weld tooling.

So as you can see if a WFI sensor is not selected where there is a magnetic field present it can cause multiple cycle time problems and unnecessary downtime. For more information on WFI sensors click here.

Liquid Level Sensing: Detect or Monitor?

Pages upon pages of information could be devoted to exploring the various products and technologies used for liquid level sensing and monitoring.  But we’re not going to do that in this article.  Instead, as a starting point, we’re going to provide a brief overview of the concepts of discrete (or point) level detection and continuous position sensing.

 Discrete (or Point) Level Detection

Example of discrete sensors used to detect tank level
Example of discrete sensors used to detect tank level

In many applications, the level in a tank or vessel doesn’t need to be absolutely known.  Instead, we just need to be able to determine if the level inside the tank is here or there.  Is it nearly full, or is it nearly empty?  When it’s nearly full, STOP the pump that pumps more liquid into the tank.  When it’s nearly empty, START the pump that pumps liquid into the tank.

This is discrete, or point, level detection.  Products and technologies used for point level detection are varied and diverse, but typical technologies include, capacitive, optical, and magnetic sensors.  These sensors could live inside the tank outside the tank.  Each of these technologies has its own strengths and weaknesses, depending on the specific application requirements.  Again, that’s a topic for another day.

In practice, there may be more than just two (empty and full) detection points.  Additional point detection sensors could be used, for example, to detect ¼ full, ½ full, ¾ full, etc.  But at some point, adding more detection points stops making sense.  This is where continuous level sensing comes into play.

Continuous Level Sensing

Example of in-tank continuous level sensor
Example of in-tank continuous level sensor

If more precise information about level in the tank is needed, sensors that provide precise, continuous feedback – from empty to full, and everywhere in between – can be used.  This is continuous level sensing.

In some cases, not only does the level need to be known continuously, but it needs to be known with extremely high precision, as is the case with many dispensing applications.  In these applications, the changing level in the tank corresponds to the amount of liquid pumped out of the tank, which needs to be precisely measured.

Again, various technologies and form factors are employed for continuous level sensing applications.  Commonly-used continuous position sensing technologies include ultrasonic, sonic, and magnetostrictive.  The correct technology is the one that satisfies the application requirements, including form factor, whether it can be inside the tank, and what level of precision is needed.

At the end of the day, every application is different, but there is most likely a sensor that’s up for the task.

Magnetic Linear Encoders – Tape Magnetization Technology

bmlPrecision Tape Magnetization Leads to Precision Position Measurement

The key to ultimate accuracy for any magnetic linear encoder system is the precision of the magnetic encoding on the tape (sometimes called a scale). Sensors inside the encoder read head respond to the strength and position of the magnetic flux coming from the magnetic poles encoded onto the tape. Precise placement of these poles – and just as importantly, the precise shape of these poles – is critical to the ultimate level of accuracy that can be delivered by the encoder system. Any inaccuracy in the position, strength, or shape of these fields will directly influence the accuracy of the encoder’s indicated position. This effect is amplified with increasing gap distance between the tape and the encoder read head. The further away from the tape, the weaker and more indistinct the shape and position of the magnetic poles becomes.

Not All Magnetic Tapes Are Created Equal

Many magnetic encoder tapes on the market are surface magnetized utilizing the conventional parallel magnetization process. This is a straightforward technique that results in an encoder tape that meets performance specifications at close gap settings between the read head and the tape.

A more recent tape magnetization process called Permagnet® produces magnetic poles with improved control over their strength, shape, and location on the tape. The best way to appreciate the advantages of this technology is to compare magnetic scans of some conventionally magnetized tapes to some examples of tapes encoded with the Permagnet® process. Note the visible difference in sharp definition of the magnetic poles that is produced by the newer technology.

Conventionally Magnetized Tape – Sample #1

Sample #1 - Conventionally magnetized tape: 2 mm pole spacing, scanned at a distance of 0.2mm from the tape surface
Sample #1 – Conventionally magnetized tape: 2 mm pole spacing, scanned at a distance of 0.2 mm from the tape surface
Sample #1 - Conventionally magnetized tape: 2mm pole spacing, scanned at a distance of 0.8 mm from the tape surface
Sample #1 – Conventionally magnetized tape: 2 mm pole spacing, scanned at a distance of 0.8 mm from the tape surface

Tape Magnetization with Permagnet® Technology – Sample #2

Sample #2 - Permagnet tape: 2mm pole spacing, scanned at a distance of 0.2 mm from the tape surface
Sample #2 – Permagnet tape: 2mm pole spacing, scanned at a distance of 0.2 mm from the tape surface

Sample #2 – Permagnet® tape: 2 mm pole spacing, scanned at a distance of 0.8 mm from the tape surface.
Sample #2 – Permagnet® tape: 2 mm pole spacing, scanned at a distance of 0.8 mm from the tape surface.

The stronger, more sharply-defined magnetic poles produced by Permagnet® technology enables encoders to be more tolerant of variation in the working distance between the encoder read head and the tape. Reduced dispersion and distortion of the magnetic fields at any distance within the specified working range reduces the influence of distance variation on the accuracy of the position measurement in real-world applications.

Summary of Application Benefits

  • Improved linearity at close working distances for ultimate system accuracy
  • Improved linearity at longer working distances
  • Higher tolerance to deviations in the working distance, with reduced non-linearity
  • Less need to closely control the working distance in the application, saving cost by reducing painstaking setup and alignment effort
  • Full system accuracy, even if gap distance varies during operation
  • Better linearity for any given pole spacing on the tape

We Don’t Make Axes Out of Bronze Anymore

Every technology commonly in use today exists for a reason.   Technologies have life cycles: they are invented out of necessity and are often widely used as the best available solution to a given technical problem.  For example, at one time bronze was the best available metallurgy for making long-lasting tools and weapons, and it quickly replaced copper as the material of choice.  But later on, bronze was itself replaced by iron, steel, and ultimately stainless steel.

When it comes to detecting the presence of an object, such as a moving component on a piece of machinery, the dominant technology used to be electro-mechanical limit switches.  Mechanical & electrical wear and tear under heavy industrial use led to unsatisfactory long-term reliability.  What was needed was a way to switch electrical control signal current without mechanical contact with the target – and without arcing & burning across electrical contacts.

Example of an inductive proximity sensor
Example of an inductive proximity sensor

Enter the invention of the all-electronic inductive proximity sensor.  With no moving parts and solid-state transistorized switching capability, the inductive proximity sensor solved the two major drawbacks of industrial limit switches (mechanical & electrical wear) in a single, rugged device.  The inductive proximity sensor – or “prox” for short – detects the presence of metallic targets by interpreting changes in the high-frequency electro-magnetic field emanating from its face or “active surface”.  The metal of the target disrupts the field; the sensor responds by electronically switching its output ON (target present) or OFF (target not present). The level of switched current is typically in the 200mA DC range, which is enough to trigger a PLC input or operate a small relay.

In my next post, I will explain the do’s and don’ts for applying inductive prox sensors.

Aw, yiss…BiSS!

BiSSThere’s a cool new serial data interface coming on the scene.

It’s called BiSS (Bi-Directional Synchronous Serial), and is an open-source, free-to-license digital interface for sensors and actuators. BiSS is hardware compatible to the industrial standard SSI (Serial Synchronous Interface) but offers additional features and options. Here are a few highlights:

  • Serial Synchronous Data Communication
  • 2 unidirectional lines Clock and Data
    o Cyclic at high-speed (up to 10 MHz with RS422 and 100 MHz with LVDS)
    o Line delay compensation for high-speed data transfer
    o Request processing times for data generation at slaves
    o Safety capable: CRC, Errors, Warnings
    o Bus capability for multiple slaves and devices in a chain
  • Unidirectional
    o BiSS C (unidirectional) protocol: Unidirectional use of BiSS C
  • Bidirectional
    o BiSS C protocol: Continuous mode
  • Actuators
    o Operate actuators via two additional lines

bmlFor more information and FAQs, visit http://www.biss-interface.com/

Click here to learn about absolute, magnetically coded position measurement systems for large measurement sections with BiSS interface.