When machine builders build assembly machines for their customers they want to keep the wiring as clean and clear as possible for an attractive machine but more importantly the ease of troubleshooting in the event of a failure. Simplifying connections with unnecessary cables and splitters not only makes it easier for the maintenance technicians to trouble shoot but it also saves the company money with unneeded product and components to inventory and maintain.
In the past it was common practice to wire sensors and cables all the way back into a terminal box located in sections of an assembly line. This could be very difficult to track down the exact sensor cable for repair and furthermore in some cases five meter cables or longer would be used to make the longer runs back to the terminal box. The terminal boxes would also get very crowded further complicating trouble shooting methods to get the assembly lines back up and running production. This is where Interface Blocks come in and can provide a much cleaner, effective way to manage sensor connections with significantly decreasing downtime.
For example: If our customer has a pneumatic cylinder that requires two sensors, one for the extended position and one for the retracted positon. The customer could run the sensor cables back to the Interface Block. This sometimes is used with a splitter to go into one port to provide the outputs for both sensors only using one port. Now we can take this a step further by using twin magnetic field sensors (V-Twin) with one connection cable. This example eliminates the splitter again eliminating an unneeded component. As you can see in the reference examples below this is a much cleaner and effective way to manage sensors and connections.
The simplest magnetic field sensor is the reed switch. This device consists of two flattened ferromagnetic nickel and iron reed elements, enclosed in a hermetically sealed glass tube. As an axially aligned magnet approaches, the reed elements attract the magnetic flux lines and draw together by magnetic force, thus completing an electrical circuit.
While there are a few advantages of this technology like low cost and high noise immunity, those can be outweighed by the numerous disadvantages. These switches can be slow, are prone to failure, and are sensitive to vibration. Additionally, they react only to axially magnetized magnets and require high magnet strength.
Magnetoresistive Sensors (GMR)
The latest magnetic field sensing technology is called giant magnetoresistive (GMR). Compared to Reed Switches GMR sensors have a more robust reaction to the presence of a magnetic field due to their high sensitivity, less physical chip material is required to construct a practical GMR magnetic field sensor, so GMR sensors can be packaged in much smaller housings for applications such as short stroke cylinders.
GMR sensors have quite a few advantages over reed switches. GMR sensors react to both axially and radially magnetized magnets and also require low magnetic strength. Along with their smaller physical size, these sensors also have superior noise immunity, are vibration resistant. GMR sensors also offer protection against overload, reverse polarity, and short circuiting.
One of the basic differences is that detection method that each solution utilizes. Magnetic field sensors use an indirect method by monitoring the mechanism that moves the jaws, not the jaws themselves. Magnetic field sensors sense magnets internally mounted on the gripper mechanism to indicate the open or closed position. On the other hand, inductive proximity sensors use a direct method that monitors the jaws by detecting targets placed directly in the jaws. Proximity sensors sense tabs on moving the gripper jaw mechanism to indicate a fully open or closed position.
Additionally, each solution offers its own advantages and disadvantages. Magnetic field sensors, for example, install directly into extruded slots on the outside of the cylinder, can detect an extremely short piston stroke, and offer wear-free position detection. On the other side of the coin, the disadvantages of magnetic field sensors for this application are the necessity of a magnet to be installed in the piston which also requires that the cylinder walls not be magnetic. Inductive proximity sensors allow the cylinder to be made of any material and do not require magnets to be installed. However, proximity sensors do require more installation space, longer setup time, and have other variables to consider.
One trend we see today in many applications is the need for smaller low profile proximity sensors. Machines are getting much smaller and the need for error proofing has ultimately become a must for such applications in the Stamping and Die industry. Stamping Die processes can be a very harsh environment with excessive change overs to high speed part feed outs when running production. In many cases these applications need a sensor that can provide 5mm of sensing range however they simply do not have the room for an M18 sensor that is 45 to 50mm long. This is where the “FlatPack” low profile sensor can be a great choice due to their low profile dimensions.
Proximity sensors have proven time and time again to reduce machine crashes, part accuracy and proper part location. Sensors can be placed in multiple locations within the application to properly error proof “In Order Parts” (IO) for example detecting whether a punched hole is present or not present to ensure a production part is good. All of this adds up to reduced machine downtime and lower scrap rates that simply help a plant run more efficiently.
So when selecting proximity sensors and mating cables it is very important to select a sensor that A) mechanically fits the application and B) offers enough sensing range detection to reliably see the target without physical damage to the sensor. Remember, these sensors are proximity sensors not positive machine stops. Cables are also key to applications, it is important to pick a the proper cable needed for example an abrasion resistant cable may be needed due to excessive metal debris or a TPE cable for high flex areas.
Below both sensors have 5mm of sensing range:
Below both sensors have 2mm of sensing range:
You can see that in certain process areas “FlatPack” low profile sensors can provide benefits for applications that have space constraints.
For more information on proximity sensors click here.
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.
But 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!
Applications 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 www.balluff.us.
When 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 www.balluff.us.
In my previous blog post we covered the Anatomy of a High Pressure Proximity Sensor. That post covered the different mechanical housing designs and special properties that go into high pressure sensor products with discrete outputs. That is great information to know when specifying the correct sensor for a particular application. In today’s competitive market and constant goals to improve processes, sensor’s that offer continuous feedback are required.
Hydraulic systems regulate speed of an actuator by regulating flow rate. The flow rate determines the speed of the cylinder spud that actuates inside the system. For example, an analog sensor can provide measurement to the controls with indication of slowing down or speeding up the actuator based on the analog feedback from the sensor in regard to position of the tapered section of the actuator. So, if the internal target gets larger with more position movement (stroke) the distant measurement changes and indicates that the end of stroke is near causing the controller to initiate a soft stop. This provides better control of the system offering a more efficient reliable process.
Analog Inductive sensors provide an absolute voltage or current signal change proportional to the distance of a ferrous target. In high pressure applications that require more position feedback, an analog distance sensor can offer a solution as they also offer high – strength stainless steel housings with special sealing designs that allow pressure up to 500 bar and 85°C temperature ratings making them an ideal solution for valve speed control and soft starts with a non – contact design.
More information on high pressure analog inductive sensors is available on the Balluff website at www.balluff.us.
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.
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.
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.
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.
Note: (-) 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.
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.
WFI 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.