Anatomy of a High Pressure Inductive Proximity Sensor

Some industrial applications will require a sensor with special properties. This type of sensor offering is needed especially when pressure comes to play. In a wide range of hydraulic cylinder and valve applications high pressure sensors are exposed to hostile environments and are subject to pressure that a standard sensor simply cannot hold up in. For example 350 bar of pressure can be detrimental to a standard sensor as it is not designed for a pressure application.

High pressure inductive sensors are designed to withstand the severe duty of a high pressure application with product features like corrosion – resistant housing materials, high strength ceramic sensing faces and special sealing techniques such as undercut housings with sealing and support rings. This is very important because not only do we need to have a sensor that can withstand pressure on the face of the sensor without damage we also need to make sure we can keep the hydraulic fluid inside the cylinder or valve where it belongs.

In the photo below you will notice the undercut area at the sensing face of the sensor along with an O-ring and supporting backing ring to make sure the application is sealed tight.

installation instruction Installation Photo

There are several common sizes for different types of cylinder and valves however the same principle applies. Below is an example of a flange mount style offering. This type of sensor takes a different design approach that is bolted to the top side of a cylinder with a sealing O-ring under the mounting point.

Strokemaster Diagram

strokemaster photo

It’s also important to know what form factor is needed when specifying a high pressure inductive sensor. Typically you will see pressure options from 50 up to 500 bar. The dimensions of the cylinder or valve will determine what type of high pressure sensor is needed.


For more information on high pressure Inductive Sensor click here.

DC Does Have Its Benefits

My blog this time was supposed to be about photoelectric basics, however, I recently had a discussion with an individual who asked why the market does not offer more AC sensors.  In thinking about our discussion I thought this would make an interesting blog and perhaps would spark (no pun intended) some comments from our readers.

 Why DC control circuits are more common than AC and what benefits do they provide? 
minifamilyWith machines getting smaller and faster, and costs becoming more of a concern DC sensors and components solve these issues.  The circuit boards are smaller which means the sensors can be smaller and lighter thus the machines can move faster due to lighter loads.  DC sensors are typically less expensive and a larger selection of products exists to solve more of the demanding applications seen today.

Some regulations go into effect at the 50 – 60 volt threshold and since a vast majority of DC control circuits are 24 volt these regulations can be avoided.  DC control circuits are more universally accepted than AC plus the fact DC power supplies are getting less expensive.  Today’s newly designed DC circuits consume less power which means smaller power supplies can be used.  Another advantage of the DC power supply is if there is a short circuit the power supply folds back and will resume full power when the short is removed.

Not only are there more sensor options available there are more and faster interface cards for the most common control device used today, the PLC.  DC sensors and components do not have the current leakage that their AC counterparts have.  That being said, when using an AC sensor with the higher leakage, frequently pull down resistors are required to prevent the leakage current from causing false inputs to the PLC.

In addition to the PLC interface, more and more manufacturers use DC interfaces to their electronic devices.  With AC controls you have to use relays for interface which can add to cycle times.  A real money saver is being able to run instrumentation and communication cables with DC controls in the same conduit or cable tray.

DC is inherently faster than AC which means faster response.  With more and more cycle times being reduced to achieve faster processes milliseconds can really add up.  An AC signal introduces approximately an 8 msec delay in actuation of a device, however, this delay time is very unpredictable.

Typically, AC is used on the outputs of PLC’s to turn on motor control starters, larger solenoid valves, and higher current devices.  Also, AC circuits are going to be more immune to noise that would cause problems on DC circuits.  In some cases it makes sense to use an AC sensor especially if there is a long run of conduit down a conveyor with one motor and one sensor.  Those wires can be run together saving installation time and money.

When it comes to speed, size, and costs DC controls seem to provide more benefits than AC.  What are your thoughts?

Back to the Basics: How Do I Wire a DC 2-wire Sensor?

In one of my previous post we covered “How do I wire my 3-wire sensors“. This topic has had a lot of interest so I thought to myself, this would be a great opportunity to add to that subject and talk about DC 2-wire sensors. Typically in factory automation applications 2 or 3 wire sensors are implemented within the process, and as you know from my prior post a 3 wire sensor has the following 3 wires; a power wire, a ground wire and a switch wire.

A 2-wire sensor of course only has 2 wires including a power wire and ground wire with connection options of Polarized and Non-Polarized. A Polarized option requires the power wire to be connected to the positive (+) side and the ground wire to be connected to the negative side (-) of the power supply. The Non-Polarized versions can be wired just as a Polarized sensor however they also have the ability to be wired with the ground wire (-) to the positive side and the power wire (+) to the negative side of the power supply making this a more versatile option as the sensor can be wired with the wires in a non – specific location within the power supply and controls.

In the wiring diagrams below you will notice the different call outs for the Polarized vs. Non-Polarized offerings.

PolarizedDiagramsnon-polarized diagramsNote: (-) Indication of Non-Polarized wiring.

While 3-wire sensors are a more common option as they offer very low leakage current, 2 wire offerings do have their advantages per application. They can be wired in a sinking (NPN) or sourcing (PNP) configuration depending on the selected load location. Also keep in mind they only have 2 wires simplifying connection processes.

For more information on DC 2- Wire sensors click here.

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.

There’s more than just one miniature sensor technology

As I discussed in my last blog post, there is a need for miniature, precision sensors. However, finding the right solution for a particular application can be a difficult process. Since every sensor technology has its own strengths and weaknesses, it is vital to have a variety of different sensor options to choose from.

The good news is that there are several different technologies to consider in the miniature, precision sensor world. Here we will briefly look at three technologies: photoelectric, capacitive, and inductive. Together these three technologies have the ability to cover a wide range of applications.

Photoelectric Sensors

MiniPhotoelectricPhotoelectric sensors use a light emitter and receiver to detect the presence or absence of an object. This type of sensor comes in different styles for flexibility in sensing. A through-beam photoelectric is ideal for long range detection and small part detection. Whereas a diffuse photoelectric is ideal for applications where space is limited or in applications where sensing is only possible from one side.

Miniature photoelectric sensors come with either the electronics fully integrated into the sensor or as a sensor with separate electronics in a remote amplifier.

Capacitive Sensors

MiniCapacitiveCapacitive sensors use the electrical property of capacitance and work by measuring changes in this electrical property as an object enters its sensing field. Capacitive sensors detect the presence or absence of virtually any object with any material, from metals to powders to liquids. It also has the ability to sense through a plastic or glass container wall to detect proper fill level of the material inside the container.

Miniature capacitive sensors come with either the electronics fully integrated into the sensor or as a sensor with separate electronics in a remote amplifier.

Inductive Sensors

MiniInductiveInductive sensors use a coil and oscillator to create a magnetic field to detect the presence or absence of any metal object. The presence of a metal object in the sensing field dampens the oscillation amplitude. This type of sensor is, of course, ideal for detecting metal objects.

Miniature inductive sensors come with the electronics fully integrated into the sensor.

One sensor technology isn’t enough since there isn’t a single technology that will work across all applications. It’s good to have options when looking for an application solution.

To learn more about these technologies, visit

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.

Customization of RFID tag holders and mounting accessories

Does your RFID application require a customized tag holder? What about special brackets for read/write heads and processors? Don’t have the bandwidth to design the mounting hardware required for your unique application? The Balluff Customizing Group can help! If you are implementing the BIS C, BIS L, BIS M or BIS U RFID systems we will make sure you get the performance your application demands.

For several years the Balluff Customizing Group has been working directly with engineers and maintenance personal to provide design and development services for RFID mechanical accessories. The process is streamlined and very straight forward. Please contact Balluff’s Technical Support Professionals to discuss your RFID application.

Here are a few recent examples of RFID projects in the Customizing Group:

1) RFID Pistol Grip Read/Write Head for BIS M data carriers. The modular design can be used with M12, M18 and M30 tubular read/write heads for logistics tracking of incoming and outgoing shipments.


2) Keyfob with embedded BIS C data carrier. Individual access codes are programmed to the tags allowing only authorized personnel to enter restricted areas.

Keyfob Keyfob2

3) BIS M read/write data carriers embedded in stainless steel NPT plug for Production Tracking.


5 Tips on Making End-of-Arm Tooling Smarter

Example of a Flexible EOA Tool with 8 sensors connected with an Inductive Coupling System.

Example of a Flexible EOA Tool with 8 sensors connected with an Inductive Coupling System.

Over the years I’ve interviewed many customers regarding End-Of-Arm (EOA) tooling. Most of the improvements revolve around making the EOA tooling smarter. Smarter tools mean more reliability, faster change out and more in-tool error proofing.

#5: Go Analog…in flexible manufacturing environments, discrete information just does not provide an adequate solution. Analog sensors can change set points based on the product currently being manufactured.

#4: Lose the weight…look at the connectors and cables. M8 and M5 connectorized sensors and cables are readily available. Use field installable connectors to help keep cable runs as short as possible. We see too many long cables simply bundled up.

#3: Go Small…use miniature, precision sensors that do not require separate amplifiers. These miniature sensors not only cut down on size but also have increased precision. With these sensors, you’ll know if a part is not completely seated in the gripper.

#2: Monitor those pneumatic cylinders…monitoring air pressure in one way, but as speeds increase and size is reduced, you really need to know cylinder end of travel position. The best technology for EOA tooling is magnetoresistive such as Balluff’s BMF line. Avoid hall-effects and definitely avoid reed switches. Also, consider dual sensor styles such as Balluff’s V-Twin line.

#1: Go with Couplers…with interchangeable tooling, sensors should be connected with a solid-state, inductive coupling system such as Balluff’s Inductive Coupler (BIC). Avoid the use of pin-based connector systems for low power sensors. They create reliability problems over time.

Consider this when using multi-vendor IO-Link solutions

The IO-Link consortium allows for multiple master connections from DIN rail slice IP20 solutions to IP67 ports.  As usage of IO-Link has grown dramatically over the last two years and adoption of multi-vendor solutions continues to rise, there will be a point where you may encounter an alternate type of IO-Link connection for IP67 masters and devices in the market.

The specification allows for a wide variety of connectors and conductors for the IO-Link master/slave connection specifically calling out M5, M8 & M12 connectors.  The default port and pin configuration for an IO-Link master port is the M12 A-coded connection with port type A.  In IO-Link port A, the power for the IO-Link slave device is provided entirely by the pins 1&3 similar to a standard proximity sensor according to IEC 61076-2-101.  This is the most common port type in use today and is found on the widest variety of sensors and slave devices.

An alternate port type is available, IO-Link Port B, to provide galvanically isolated power to the IO-Link slave device.  In this configuration a second power supply can be added for isolated control power.  It is not widely adapted in IO-Link slave devices today but can be found in some products where this is an application requirement.  If a master or device has a port type B it must be clearly labelled on the product per the specification.


If there is not a port type identified on the device then it is assumed to be a port A type device as it is the default configuration.  Balluff IO-Link masters and devices are mostly of the type port A.  Check out Balluff’s IO-Link offering.



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