Back to Basics: The Fundamentals of a Passive RFID System

There has been a lot of talk in the industrial automation about RFID. In past blog posts we’ve discussed topics like RFID ROI and when to use IO-Link RFID. We could talk about things to consider when implementing RFID into your plant or different applications for days. In this entry, though, I’d like to get back to the basics a little bit.

Area of Application for a Passive RFID System:

RFID is used to accurately identify an object on which the tag is placed. In addition to identification, bject-specific information, like maintenance data is contained on the tag.

Typical RFID System

Typical RFID System

How It Works:

Since passive RFID tags contain no battery, the tag is powered up or “woke up” by the RF waves emitted from antenna of the same frequency. Once a tag is located in range it is powered up by the antenna and its memory can be read and transmitted to the processor. The time it takes the reader to extract information from the tag is usually measured in milliseconds.

Three Main Components of a Passive RFID System:

– A combination of a chip and internal coil. The chip is where the data is held in the memory and can contain a few bytes of data or thousands of bytes of data depending on the capacity of the chip.

RFID-AntennaAntenna – Connected to the processor by an external cable or sometimes contained inside the same housing, the antenna transmits the data to and from the tag back through the processor

RFID-Processor Processor – The role of the processor is to organize the data as it is being read or written. The processor is usually connected to a controller, like a PC or PLC, and performs the task issued by the controller.

To learn more about industrial RFID applications and components visit

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Photoelectric Output Operate Modes and Output Types

Photoelectric sensors are used in a wide variety of applications that you encounter every day. They are offered in numerous housing styles that provide long distance non-contact detection of many different types of objects or targets. Being used in such a variety of applications, there are several outputs offered to make integration to control systems easy and depending on the sensing mode when the output is activated in the presence of the target.

DiffuseDiffuse sensors depend on the amount of light reflected back to the receiver to actuate the output. Therefore, Light-on (normally open) operate refers to the switching of the output when the amount of light striking the receiver is sufficient, object is present. Likewise, Dark-on (normally closed) operate would refer to the target being absent or no light being reflected back to the receiver.

RetroreflectiveRetroreflective and through-beam sensors are similar in the fact they depend on the target interrupting the light beam being reflected back to the receiver. When an object interrupts the light beam, preventing the light from reaching the receiver, the output will energize which is referred to as Dark-on (normally open) operate switching mode or normally open. Light-on (normally closed) operate switching mode or normally closed output in a reflex sensor is true when the object is not blocking the light beam.

signalsOutputs from photoelectric sensors are typically either digital or analog. Digital outputs are on or off and are usually three wire PNP (sourcing output) or NPN (sinking outputs). The exception to this is a relay output that provides a dry or isolated contact requiring voltage being applied to one pole.

Analog outputs provide a dynamic or continuous output that varies either a voltage (0-10 volt) or current (4-20mA) throughout the sensing range. Voltage outputs are easier to integrate into control systems and typically have more interface options. The downside to a voltage output is it should not be ran more than 50 feet. Current outputs can be ran very long lengths without worry of electrical noise. As additional advantage of the analog output is that it has built in diagnostics, at its minimum there will always be some current at the input unless the device completely fails or the wire is damaged.

Some specialty photoelectric sensors will provide a serial or network communication output for communications to higher level devices. Depending on the network, IO Link, for instance, additional diagnostics can be provided or even parameterization of the sensors. io-link
Interested in learning more about photoelectrics basics? Visit Balluff Basics library on our web site. You can also request a copy of the new Photoelectric Handbook.

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Blaise Pascal – The Ultimate Powerlifter

Our modern technological society owes a lot to the scientific work and inspiration of a 17th-century French mathematician and physicist, Blaise Pascal. Pascal was a pioneer in the fields of hydrostatics and hydrodynamics, which deal with the subject of fluid mechanics under pressure.

One of the most important physical principles he defined is known today as Pascal’s Law:

“Blaise Pascal Versailles” by unknown1

“A change in pressure at any point in an enclosed fluid at rest is transmitted undiminished to all points in the fluid.”

It is this characteristic of fluids held in containment that allows force applied to a fluid in one location to be delivered to another remote location. A well-known example would be the hydraulic brake system in a car. Mechanical pressure from the driver’s foot is transferred to the brake fluid through a master cylinder. This pressure is then instantly communicated to braking cylinders located at each wheel, causing them to apply mechanical force to press friction pads against a brake drum or rotor, thus slowing or stopping the vehicle.

In the industrial world, the compact yet incredible power of hydraulic cylinders is constant a source of awe and amazement. Through the magic of fluid power leverage via Pascal’s Law, hydraulic cylinders are capable of generating tremendous lifting forces to move massively heavy structures.

In order for such great force to be harnessed to do useful work, it must be kept fully under control. Force that is out of control is either useless or destructive. When it comes to controlling the movement of a powerful hydraulic cylinder, the piston/ram position must be continually monitored in near-real-time.

The most popular device for measuring cylinder position is called a Magnetostrictive Linear Position Sensor. Sometimes these position sensors are called LDTs (Linear Displacement Transducer) or MDTs (Magnetostrictive Displacement Transducer). All of these terms refer to the same type of devices.


To get an idea of the power and control that is feasible with modern hydraulic cylinders and integrated cylinder position sensors, have a look at this amazing video from ALE Heavylift. The topside of a giant offshore oil platform was jacked up 131 ft (40 m) and then skidded horizontally a distance of 295 ft (90 m) to place it on top of its supports. Imagine the incredible synchronization of speed, position, and operational sequencing needed to safely lift and place such a massive structure.

For more information about magnetostrictive linear position sensors for hydraulic cylinders, visit the Balluff website at

1. “Blaise Pascal Versailles” by unknown; a copy of the painture of François II Quesnel, which was made for Gérard Edelinck en 1691. – Own work. Licensed under CC BY 3.0 via Commons –

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You Should be Participating in #MFGday!

MFG Day TourWow! Talk about a fun, energizing and educational event for employees, students and the community. Balluff just completed our first year participating in Manufacturing Day as a host company. We had over 100 students, kids, parents, teachers, customers and retirees visit our facility over 6 hours during a rainy Friday. We ran tours every hour that consisted of a hands-on lab that taught the difference between manual and automated processes, tours of our production and warehouse facility and a review of how automation is used in a variety of industries.During any downtime the participants could also visit our newly constructed Automation in Action Demo Van (Twitter: @balluffbus) and learn about how sensor technologies support automation in manufacturing.

The high school students that visited loved the hands on applications and asked questions with an engaging and excited spirit that was inspiring. We engaged with some home schooling groups and had a great turnout from those folks as well. I loved how eager all the kids were to learn about sensors and automation. Even the big kids found value and inspiration. The posts on the Balluff facebook page I believe say it all:

Thank you guys so much for the tour! We had fun and learned a lot. The kids have been playing make believe with sensors and their badges since we got home.

Thank you for the wonderful tour! My husband and I really enjoyed it! It’s nice seeing the mechanics behind the some of the equipment that we’ve used in the chemical industry and manufacturing processes!

But the best part of this event was how inspiring it was to our employees. Both those giving the tours, participating at the signup table or hands-on labs and even those who were not direct participants. Everyone was so proud and excited to share with the community our passion for automation and how committed we are to our customer’s success. Manufacturing is a great industry, with great opportunities and its great to share that spark with others.

Thank you to everyone who attended, participated in and supported this great event! You can see more photos from the event on our Flickr page.

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Magnetic Field Sensors – Not Just For Cylinder Applications

When thinking of magnetic field sensors the first form factors that come to mind are C or T slot style sensors designed to fit into specific cylinders. These popular types of magnetic field sensors are used to sense through the aluminum body of a cylinder and detect a magnet inside the housing (cylinder wall) of the cylinder. This is a very reliable sensor type that simply detects the extended or retracted position of a cylinder.

BMF Application2But did you know you can achieve a wide range of applications when using tubular style magnetic field sensors? These types of magnetic field sensors typically come in tubular sizes that range from 6.5mm – M12x1 and can be used with various size magnets to cover several application specifications. These offerings offer precise reliable switch points, robust housings for harsh applications and they are also short circuit protection. For example, if a target is too far away for a traditional inductive proximity sensor or maybe too reflective for a photoelectric sensor, a tubular magnetic field sensor and a mating magnet can reliably sense that magnetic field from 90 mm away! Great distance, switching frequency at 10k Hz, and with a small mounting footprint!

BMF ApplicationApplications include pallet detection, high speed impeller, gear, cog detection, many more in a wide range of industry disciplines.

To learn more about magnetic field sensors you can visit

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Isn’t a bar code just a bar code?

Bar codes are normally read via a red line laser scanner, or a camera with decoding and positioning software.

There are 3 main types of bar codes.

1D (one dimensional), 2D (two dimensional) and a different type of 2D code is QR (Quick response) codes that we use today.

Each code has a little different attribute and how it’s read.

 1D bar codes are the ladder line bar codes you typically see in a grocery store, on merchandise and packaging.

While there are many different types of 1D bar codes and how they decipher a code the appearance is typically like the picture below.







A 2D Data Matrix code is much smaller than a 1D and can hold quite a bit more information. They can actually hold up to 2,335 alphanumeric characters.

There is redundancy built into the code, in case the code is scratched or defaced.

The code below is an example of a 2D Data Matrix code.


The code is read by utilizing a camera and decoding / positioning software.

A QR Code can hold more information than a Data Matrix code.

It can decipher numeric, alphanumeric, byte/binary and kanji.

While it was 1st developed for the automotive industry tracking parts during vehicle manufacturing, it is typically linked to a website when the code is scanned with a camera in a cell phone.

An example of the QR Code is pictured below.

QR Code

The code is read by utilizing a camera and decoding / positioning software.

There are various types of vision sensors that can be used to read different types of bar codes. You can learn more on Balluff’s website at

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Inductive Sensors for Washdown Conditions

WashdownSensorsWhen selecting the proper Inductive sensor it is very important to understand the type of application environment the sensor will be installed in. In previous posts, I have blogged about various types of sensors and how they fit into the application mix. For example, a welding application will need specific sensor features that will help combat the normal hostilities that are common to heat, weld spatter and impact due to tight tolerances within the fixture areas.

Inductive sensors are also used more and more in aggressive environments including machine tools, stamp and die, and food and beverage applications. Many times within these types of applications there are aggressive chemicals and cleaners that are part of the application process or simply part of the cleanup procedure that also
mandates high pressure wash down procedures.

So, when we have a stamping or food and beverage application that uses special oils or coolants we know a standard sensor is on borrowed time. This is where harsh environment sensors come in as they offer higher IP ratings with no LED function indicators that seals the sensor to withstand the harshest processes. They also will have high grade stainless steel housings special plated electronics along with additional O-rings making them ideal for the most hostile environment.


  • High grade stainless steel housing
  • No LED indicator
  • Gold plated internal contacts
  • Additional sealing O-rings
  • Increased IP ratings
  • Higher temperature ratings

For more information on inductive sensors for harsh environments you can visit the Balluff website at

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Why Train on Industrial Ethernet?

trainingAn industrial Ethernet network is vastly different from an office Ethernet network in several key ways, and the key to optimizing your industrial network in light of these differences, is hands-on training.

First of all, the environment in industrial applications can degrade the actual cable itself. Some cable manufacturers actually rate their cables’ ability to withstand these environmental factors. They use the acronym MICE, and rate the cable as appropriate for one of three environments: M1I1C1E1 for office environments, M2I2C2E2 for light industrial environments, and M3I3C3E3 for industrial environments. The letters actually stand for: Mechanical factors such as shock and vibration, Ingress from moisture, Climatic factors such as temperature and sunlight, and Electromagnetic interference such as noise caused by inductive loads, welders, variable frequency drives, etc. Other cable vendors observe the recommendations of ODVA and offer cables that are ODVA compliant.

Secondly, industrial Ethernet networks can have a high amount of multicast traffic. In the early years of Ethernet hubs were used to link devices. The problem is that information coming into one port of a hub was redirected to all of the other ports on the hub. With the advent of switches, unicast traffic was now directed to only the port for the intended recipient device. This is true for both managed and unmanaged switches: they both handle unicast traffic well. The problem for the unmanaged switch comes when you encounter multicast traffic. Since an unmanaged switch does not employ IGMP Snooping (Internet Group Management Protocol), the switch does not know what to do with multicast traffic. It starts acting like the old hubs: it directs all multicast traffic to all ports. With a managed switch and with IGMP Snooping turned on, the switch knows exactly where to send this multicast traffic and directs it only to the intended recipients. Multicast traffic can be anything from produced tags to input modules configured for multicast. These can be very common in industrial applications using PLCs.

Thirdly, we now have tools available in many switches and routers to prioritize the traffic on an Ethernet network. This becomes especially important when you have high-speed applications, motion applications, or time synchronization applications. In the past all Ethernet data was equal. The feedback coming from a servo drive had to wait just as long as a person trying to get online with a PLC. Now many automation vendors are marking their data with priority codes. Allen-Bradley marks their data in layer three with DSCP markings, and Siemens uses layer two markings with PCP marks, for instance (a VLAN tagging mechanism). In either case, if your switch or your routers are not configured properly to recognize and use these priority codes, you are not taking advantage of the QoS feature that could help get your important data through first (Quality of Service).

Only through proper training can you learn not only what the key issues are but also how to properly deploy your hardware to fully optimize your network. Balluff offers hands-on training with actual automation equipment, switches, and routers to help you do just that. You can learn more about the courses Balluff has to offer at

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If our products could talk, what would they say?

In industrial automation we put our products through a lot. Extreme temperatures, harsh environments, and the demands of high performance can put a strain on the components of any machine. This led me to wonder, if our products could talk, what would they say?

CordsetTalkCordset: Cables have certain limpness which makes installing the cordset in automation easier to fit in tight spaces. Most cable installers prefer to have the least amount of slack in cable to prevent the cable being snagged or pulled during operations. Cables need to have a bend radius to prevent kinking of the conductors and a continuous flow of power. The bend radius is “the smallest radius of curvature into which a material can be bent without damage” (McGraw-Hill Dictionary of Architecture and Construction). Typically in a fixed (stationary) application, an unshielded sensor cable has a minimum bending radius of 8 times the outer diameter of the cable.

PowerSupplyTalkPower Supply: Everyone wants a friend. When a load is too much for one power supply, adding another power supply helps increase the voltage or current output. “The simplest method to create higher current is to connect the power supplies in parallel and leave only one supply in constant voltage mode. Some power supplies are equipped with analog control signals that allow auto-parallel or auto-tracking, a more elegant way to control multiple power supplies. Auto-parallel supplies can be controlled with a single master supply; a second advantage is that all of the master power supplies features can be used.” (Keysight Technologies) By stringing together power supplies, it allows more voltage or current but also keeps operations up and running.

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Absolute Rotary Encoder Sensing Technology: Optical and Magnetic

When it comes to selecting the most appropriate position detection technology for an absolute rotary encoder application, it’s helpful to consider the general advantages and potential disadvantages of the two most common approaches: optical and magnetic.

Optical Encoders

Example of an absolute-coded optical encoder disk

Example of an absolute-coded optical encoder disk

Internally, absolute optical rotary encoders are comprised of:

  1. An LED light source
  2. A rotating coded disk to modulate the light beam from the LED
  3. An array of photodetectors to convert the impulses of light into electrical signals.

The spinning code disk contains a series of concentric tracks that each represent one bit of resolution, and each track is associated with a separate photodetector.

Among optical encoders, there are two main variations: optical mask and optical phased-array. Optical mask encoders are the more straightforward implementation. A grated mask featuring slots of the same size as the slots in the optical disk is placed on top of the photodetectors to prevent the light spilling over from one channel to another. The chief advantage of the optical mask encoder rests in the ability of the encoder manufacturer to offer a variety of resolutions with the same photodetector array simply by changing the optical code disk and associated mask. On the downside, very high-resolution optical mask encoders require a very small air gap between the mask and the disk of about 0.001…0.003″ (25…75μm). Reliably maintaining such a tight gap requires tight manufacturing and assembly tolerances, and can lead to problems in severe shock and vibration environments.

As a result of the limitations of optical mask encoders, phased-array encoders were developed. Rather than relying on only a single detector for each channel, an ASIC (application-specific integrated circuit) provides an array of very small photodetectors for each channel. The responses of these multiple detectors are averaged, producing a more robust detection signal that is less susceptible to variation than a single detector. This additional signal robustness can be used to relax mechanical construction and assembly constraints such as disk flatness, eccentricity, and misalignment. The end result is a wider air gap tolerance for phased-array encoders compared to the optical mask types.

Both optical mask and phased-array detection schemes offer similar application advantages and disadvantages. They are immune to intense magnetic fields found around MRI machines or DC injection braking of AC induction motors. Due to the wider gap between disk and detectors, phased-array encoders are more tolerant of shock and vibration.

Regardless whether optical mask or phased-array detection is employed, both variations are rather susceptible to environmental contamination. Particulates such as dirt, dust, or powders and liquids like water or oil can block or attenuate the optical signals, leading to output errors. Another environmental consideration is that elevated temperatures and temperature variations can accelerate LED aging, leading to reduced light output and less reliable signal detection over time.

Absolute optical encoders are typically available with resolutions ranging from 10-bit (1024 pulses / 360°) to 22-bit (4,194,304 pulses / 360°).

Optical Encoder Disks

There are three popular construction methods for optical disks, each having certain advantages or disadvantages:

  1. Glass + Metal Film
    1. Very flat, allowing for tighter air gap and higher resolution
    2. Fragile; can shatter when exposed to high shock or severe vibration
  2. Metal
    1. More tolerant of high shock and vibration
    2. Higher resolutions not feasible due to weakening of the disk caused by necessarily large number of slots
  3. Mylar
    1. More robust than glass + metal
    2. Susceptible to sag and flutter, requiring a higher air gap that limits resolution

Magnetic Encoders

Example of an absolute-coded magnetic encoder disk

Example of an absolute-coded magnetic encoder disk

Absolute magnetic rotary encoders are comprised of only two components:

  1. An ASIC (application-specific integrated circuit) with integrated precision magnetic sensors
  2. A magnetically-coded rotating disk made of rubber ferrite on a metal carrier substrate

The magnetic disk employs a coding scheme called the Nonius principle, consisting of two concentric, adjacent tracks of alternating north and south magnetic poles. The number of poles on each track differs, typically by one pole. For example, the outer track may have 32 poles and the inner track 31. Going around the disk, there is a continuing shift of pole alignment between the inner and outer track. At any given position around the disk, the offset angle between inner and outer poles is unique.

Example of absolute magnetic encoder internal components

Example of absolute magnetic encoder internal components

Two magnetic field sensors inside the ASIC each produce a sinusoidal signal in response to the north and south poles as they traverse over them. The phase shift between these two signals is unique for every position around the disk. Digital electronics convert this analog phase shift into a serial digital data value corresponding to the absolute rotary position of the disk around 360° of rotation. A great advantage of magnetic encoders is that the maximum gap between the sensing ASIC and the magnetic disk surface is larger than for optical mask encoders. A typical specification for a magnetic encoder gap would be 0.012″ ±0.008″ (0.33mm ±0.2mm), compared to an optical mask encoder requiring a gap of about 0.002″ ±0.001″ (50 μm ±25μm).

Magnetic encoders are extremely robust. Virtually immune to shock and vibration, they are also impervious to many kinds of particulates and liquid contaminants, including non-magnetic (non-ferrous) metal shavings and powders. This ability to tolerate contamination largely reduces or eliminates the need for costly sealed enclosures. The primary caveats when applying a magnetic encoder are the presence of very strong magnetic fields that could disrupt the encoder’s operation and the presence of ferrous particles or dust that would be attracted to the magnetic surface, where they would potentially cause distortion of the magnetic poles.

Although magnetic encoders don’t currently offer the highest levels of resolution available with some optical encoders, they do offer more than enough resolution for a wide range of applications. Absolute magnetic encoders are available with resolutions ranging from 12-bit (4096 pulses / 360°) to 17-bit (131,072 pulses / 360°).

Comparison of Optical and Magnetic Absolute Encoder Operating PrinciplesEncoderTable

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