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Full coverage E-Stop protection around your machinery

We all know the importance of having emergency stop devices near and around machinery. There are numerous regulations (ANIS, ISO, IEC) that define emergency stop device requirements. In short they all state that they are actuated by a “single human action”, should be used to de-energize equipment to a safe state, and require a manual reset before equipment can be restarted.

Normally when we think of emergency stop (E-stop) devices we think of the simple emergency stop pushbutton. You know the large, red, mushroom-head pushbutton we frantically can press when something is wrong (someone is about to be hurt). They usually do the job just fine in simple machines and when ergonomics allow the operator to quickly and easily get to that particular pushbutton without any additional effort.

Larger Machinery and Challenging Ergonomics

What do you do when you have a large piece of machinery that you need to protect with E-stop devices? Say you have 100 feet (or longer) of conveyor? Say that 100 feet of conveyor might make a few turns or curves? What about other machines, even smaller ones, such as ones around work cells where an operator has to move a few steps in either direction around barriers? These are situations where just adding E-stop pushbuttons will result in a large number of devices just to have E-stop protection coverage. Remember, they have to operate with a single human action so it can’t involve an operator making several steps and navigating around a building column or other pieces of machinery. Overall just adding E-stop pushbuttons in these scenarios could result in excessive wiring and unnecessary complexity to the system.

A great option to the above-mentioned installations are Cable-Pull Safety switches. Cable-Pull Safety Switches are also known as E-stop pullcords, E-Cords or Emergency cable stops. Mounting one device allows the designer of the safety system, by using a length of cable, to cover anywhere from 15 meters with the most basic devices all the way up to 100 meters.

These devices also allow you to go around curves of the conveyor or machinery by using pulleys to allow the cable to move smoothly without binding.

They also incorporate a slack detection feature to prevent tampering. What this means is that the cable needs to be present and connected to the actuator with the appropriate slack in order to operate. If the cable is pulled (too tight/not enough slack), the unit will trip and open its safety contacts. Also, if someone decides to cut the cable to prevent the E-stop circuit from shutting down machinery the actuator will detect that not enough slack is present and trip as well.

Planning your system

To plan on where you are putting your Cable-Pull Safety switches you will first need to layout everywhere an operator may need to activate an E-Stop device. Take a plan view of your machinery or work area and mark this. Next determine the overall length of the area to be protected. Remember there are several options as far as length of protection is concerned and you can go around curves but will need to use pulleys. After the overall length is determined you might have to break this down into several sections using several Cable-Pull Safety switches. Now you will select your devices, cables, and associated installation hardware. For more in-depth details on design considerations and installation of Cable-Pull Safety switches take a look at the product inserts for the items we sell.

To purchase Cable-Pull Safety switches, other emergency stop devices, E-stop relays or any other safety products visit us at AutomationDirect.

Click here to read more articles related to cable-pull safety switches.

The post Cable-Pull Safety Switches appeared first on Library.Automationdirect.com.

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Programmable logic controllers (PLCs) are now gaining information technology (IT) abilities to interact directly with the internet, creating new automation and information possibilities.

Bill Dehner, a Technical Marketing Manager at AutomationDirect, authored an article for the July 2019 issue of Control Engineering titled Benefits of Connecting a PLC to the Internet. Here’s a summary, click on the link above for the full text.

PLCs have traditionally excelled at using wired inputs and outputs (I/O) to execute automation logic quickly and reliably. Now, users are recognizing the internet contains a wealth of information useful for PLC applications either directly in the logic or for operator displays. Many websites can programmatically deliver information such as weather forecasts, sunset/sunrise times or even commodity prices. With the right software tools built-in, modern PLCs can access this information.

Web Browser Basics

When users type a web address into a browser address bar, they are entering what is called a uniform resource locator (URL) which points to a specific domain and webpage. Accessing the internet requires a capability called hypertext transfer protocol (HTTP), which formats information as lightweight text files. Entering a URL generates an HTTP request to a web server, which responds with a lightweight HTTP response to populate the browser display.

Understanding APIs

The process is a little different for PLCs to access the internet. Many websites offer application programming interfaces (APIs), which allow programmable systems to request information. The data is returned in a JavaScript object notation (JSON) format which must be parsed to extract what is needed. An internet search reveals which websites offer APIs for accessing desired information. Some APIs allow free and complete access, while others offer limited access or charge a subscription fee.

Working with JSON Files

JSON responses are received as a compact ASCII string, which is not very human-readable. Reorganizing the content with a compatible text editor reveals the layered and nested structure of information objects in a JSON file.

A typical JSON data payload requires extensive parsing to extract the desired data.

Bill recommends users gather a few helpful tools before embarking on a project to link a PLC with a website:

This color-highlighted JSON sample shows the layered nature of information, which contains human-readable data ready for parsing by software.

One is the open-source Wireshark, which will expose the HTTP request and response packets. Another is a text editor to facilitate viewing JSON responses. Any text editor will do, but there are many free editors that make the job much easier by providing enhanced displays of JSON formatted content.

Every PLC is different, but for this article Bill looks at the special instructions provided with AutomationDirect BRX PLCs and Do-more Designer software. The first is a HTTPCMD block for requesting information from a target API server, while the second is a JSONPARSE block used to drill into object layers within a JSON payload.

This HTTPCMD block in an AutomationDirect BRX PLC enables the PLC to initiate a request to an internet website API to obtain data.

This JSONPARSE block in an AutomationDirect BRX PLC is needed so the PLC can extract the desired information from within the JSON payload.

With these basic understandings, Bill moves on to a practical example.

Checking the Temperature via the Internet

Bill works through some details of how to obtain the current local temperature from a website like AccuWeather using HTTPCMD and JSONPARSE commands. He first describes how to register and obtain a private user API key, and then discusses the programming to make it happen.

In actual runtime, the PLC will be configured to issue HTTP commands with the proper request strings. As each response is received, the PLC needs to place the data in string variables and then issue successive JSON parse instructions to drill down to the desired data.

The AccuWeather API offers options to request information based on major city, latitude/longitude or ZIP code. For this example, Bill uses the ZIP code approach, a two-step process. First the user must use a “get” method of “postal code search” to obtain a location “key”, and they can then use that key with a “get” method of “current conditions”. Finally, they can parse the JSON results to get the temperature.

Playing it Safe

Users must always take steps to ensure network security is preserved any time an industrial device connects to the internet. For this simple example, the end user might be better served by installing a local temperature transmitter. However, the internet offers plenty of useful information which can’t be instrumented locally, such as commodity prices. With a little thought and some programming effort, users can take advantage of PLC-based HTTP and JSON instructions to add a new level of functionality to applications.

The post Benefits of Connecting a PLC to the Internet appeared first on Library.Automationdirect.com.

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Hammond HPS Spartan® industrial open core control transformers offer an efficient and economical solution for applications where high inrush or machine tool duty are not necessary. These transformers are open style units in ratings from 50VA up to 5000VA. Units from 50VA to 3000VA (30 amps) include molded terminal blocks. Optional finger guards and a fuse block adapter kit are available.

Four series of open core control transformers are available from 480×600 VAC, 240×480 VAC or 208×416 VAC to 120×240 VAC and 120×240 VAC to 12×24 VAC. HPS Spartan open core control transformers are ideally suited for general purpose, industrial and light duty loads and are well suited for HVAC applications, signal and alarm systems, and motor control circuits.

Spartan open core control transformers start at $29.75 and have a 15-year warranty.

Learn more by visiting: www.automationdirect.com/open-core-transformers

About AutomationDirect:

In business since 1994, AutomationDirect is a distributor offering thousands of industrial automation products for electrical control systems, including PLCs, operator interfaces, AC drives, motors, stepper systems, sensors, motor controls, enclosures and more. Their prices are typically well below the list price of more traditional automation companies because of their business model and focus on efficiency and the majority of their products are stocked for same-day shipping. Plus, get free two-day delivery on orders over $49; some limitations apply. For more information, contact them at 800-633-0405 or visit www.automationdirect.com.

Editorial Contact:              Tina Gable

Phone:                                678-455-1845

Email:                                tgable@automationdirect.com

The post Single-Phase Open Core Industrial Control Transformers from AutomationDirect appeared first on Library.Automationdirect.com.

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The “Internet of Things” for industrial applications (IIoT) allows greater visibility and access to machine and process data through cloud computing. The STRIDE Pocket Portal is a low-cost ($120.00) industrial wireless IoT end-to-end cloud data logger that connects industrial equipment and sensors to the cloud.

The Pocket Portal has an RS-485/power port, input/output port, browser interface, and provides limited control with Modbus RTU write capability (up to 115.2k baud) and 3VDC discrete output logic. Unmonitored devices can be IoT connected and become monitored quickly with Modbus RTU, 4 digital and 2 analog inputs. A Modbus device and up to four discrete outputs can be remotely controlled using the Pocket Portal mobile app.

The Pocket Portal IoT solution from AutomationDirect requires a Wi-Fi internet connection and a monthly data subscription.

Learn more by visiting: www.automationdirect.com/pocket-portal

About AutomationDirect:

In business since 1994, AutomationDirect is a distributor offering thousands of industrial automation products for electrical control systems, including PLCs, operator interfaces, AC drives, motors, stepper systems, sensors, motor controls, enclosures and more. Their prices are typically well below the list price of more traditional automation companies because of their business model and focus on efficiency and the majority of their products are stocked for same-day shipping. Plus, get free two-day delivery on orders over $49; some limitations apply. For more information, contact them at 800-633-0405 or visit www.automationdirect.com.

Editorial Contact:              Tina Gable

Phone:                                678-455-1845

Email:                                tgable@automationdirect.com

The post STRIDE Pocket Portal IoT Bridge Cloud Data Logger with IO from AutomationDirect appeared first on Library.Automationdirect.com.

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Pneumatics are often the best fit for executing mechanical motion in a reliable, simple, and cost-effective manner.

Pat Phillips is the Product Manager for Fluid Power and Mechanical products at AutomationDirect, and he authored an article for the June 2019 issue of Tech Briefs titled Pneumatics for Mechanical Motion. Here’s a summary, click on the link above for the full text.

For equipment and machinery, fluid power is a term describing how mechanical motion can be achieved via hydraulics using incompressible liquids, or pneumatics using compressible gases like air or nitrogen. Pneumatics provides several advantages over hydraulics in many applications and has been a popular choice for industrial applications for over 100 years. Many consider compressed air a fourth utility after electricity, natural gas and water.

Typical Applications

Automated equipment commonly requires two-position and multi-position motions like clamping, gripping, positioning, lifting, pressing, shifting, sorting and stacking. For instance, a pick-and-place machine could use pneumatics to move a gripper through vertical and horizontal motions. Variable force control for applications such as tensioning and embossing is also possible.

Power Transmission Options

Pneumatic and hydraulic systems easily create linear motion using cylinders, whereas electrically driven systems would usually require other mechanisms to translate rotational into linear motion. Here is a table comparing linear motion with pneumatic, hydraulic and electric methods.

This table compares pneumatic, hydraulic, and electrical means of producing linear mechanical motion.

Some machines may operate using pneumatics entirely, but it is also common for larger machines to use two or three of these power transmission methods.

Function, Simplicity And Economy

Fluid power systems typically produce more power in a smaller footprint than electric systems, with less complex automation integration. Hydraulic systems can be the most expensive method and are best used where the high peak power output is required. Pat describes other pneumatic advantages:

Pneumatic equipment generally has lower up-front design requirements than other options and is overall the least expensive. Not only are the installation materials and components relatively economical, but once a pneumatic system is in operation, the maintenance such as replacing seals or even a whole cylinder is often much cheaper than servicing, let alone replacing, an electric actuator. Troubleshooting can also be easier for pneumatic systems compared to electric.

There are some pneumatics downsides. Older systems have been regarded as noisy, but this has been largely remedied by modern components. Electrically-driven compressors are required to provide a source of pressurized air, adding energy conversion costs.

Pneumatic Hardware Basics

Most industrial facilities already have compressed air systems in place, and once it is delivered to a machine it is handled by these common pneumatic components:

  • Air preparation system (shutoff/lock-out, combination filter/regulator, soft start valve)
  • Tubing, hoses, and distribution manifolds
  • Push-to-connect fittings
  • Control valves and manifolds (manual, air pilot, solenoid-operated)
  • Air cylinders and actuators
  • Cylinder position sensors
  • Discrete pressure switches
  • Specialty components and accessories
Common pneumatic components include regulators, individual solenoid valves, solenoid manifolds, actuators and fittings.

A basic pneumatic system would include air preparation, tubing, a control valve and a cylinder.

In the article, Pat details the functionality of each component, and also points out some good design practices.

The most basic elements of any pneumatic system include air preparation, tubing and hoses, control valves, cylinders and accessories.

An electrically operated soft-start valve serves two purposes. The first is to slowly pressurize the downstream system when energized so devices don’t slam into position. The second is to quickly dump air pressure downstream during an emergency stop, guard open, or similar safety event so actuated equipment stops as quickly as possible.

There are many options when designing pneumatic systems. Users can get quite elaborate, but the basics are quite straightforward.

Pneumatic Design Basics

Pat says designers should consider the mechanics first, and the automation features like control valves and position switches second.

The best design practice is to start at the actuators and mechanically determine the required force, stroke length, and speed. This will drive the compressed air requirements, from which the designer can work backwards to size the upstream supply elements.

Electric motion systems can offer highly accurate and programmable motion, and hydraulic systems are sometimes needed to achieve very high levels of force. But for many industrial equipment applications, the scales are tipped in favor of pneumatic systems for achieving mechanical motion because they offer the best combination of functionality, simplicity and economy.

Read more articles about pneumatics here.

The post Pneumatics for Mechanical Motion appeared first on Library.Automationdirect.com.

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Specifying Performance Instead of Parts

Specifying performance instead of parts when purchasing machines and process skids cuts costs, reduces lead time and guarantees reliable operation.  Many plants and facilities rely on pre-packaged machines and process skids purchased from original equipment manufacturer (OEM) suppliers. They want the components installed in this equipment to match what they currently use to the greatest extent possible to minimize spare parts stocking and improve their familiarity with the equipment.
However, putting too much effort into specifying skids to a very detailed level comes at a cost.

Read more

A Look at the Importance of Industrial Safety Devices

There are safety related features in practically every device we use, industrial and non-industrial. Electrical devices and appliances have housings that protect consumers from electrical hazards. Motorized devices have housings intended to prevent any possible injury to users from dangerous moving parts and/or electrical components. Industrial facilities have many safety features including safety signs that warn workers of possible hazards, and all equipment and machinery have pushbuttons, switches, shields and other devices intended to prevent any possible injury to workers and operators.

Read more

Now Available
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More Capabilities for the Productivity1000 PLC

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Additional BRX Analog and Temperature I/O Expansion Modules

 Analog I/O Modules starting at $134.00

Capacitive Proximity Sensors with Potentiometer Adjustment

 Starting at $61.00

Slim Interface Electro-Mechanical Relays

 Starting at $6.25​​

Regulations Require Surge Protection for Safety Circuits

Safety considerations are crucial for industrial machinery design, and in recent years the bar has been raised many times to provide improved protection for workers. For example, emergency stop (e-stop) and safety interlock circuits have long been part of the applicable codes. Now, new codes recognize that safety interlock circuits also need surge protection.

Read more

White Paper – Safety Components on Guard

Many safety standards and specifications come into play for protecting personnel around automated equipment. Machine safety requires comprehension of and adherence to all local, national and/or international safety codes to provide the proper safeguards. While that’s beyond the scope of this white paper, a brief introduction of safety standards for guarding is worth consideration.

Read the white paper
eBook – Practical Guide to Pneumatics & Slide Chart Offer

Our Practical Guide to Pneumatics Handbook is for users who wish to advance their pneumatic knowledge. It covers a wide range of topics such as circuit symbols, component capability, integrating pneumatics with controls as well as improving pneumatic efficiency.
Fill out the form to receive your free Pneumatic Fittings Slide Chart.
This slide chart makes it easy to select the right fitting from our wide selection of threaded Pneumatic fittings. Simply point the arrow at the fitting type and tube size – and read the part number from the thread size window. English thread sizes are shown on the inside, metric types are on the back.

Download the FREE eBook

Introducing Mosaic Safety Controller Systems

Quick overview of the Mosaic Modular Safety Controller from AutomationDirect.com. Learn why so many folks are switching from discrete safety relays to expandable relay safety controllers when their system requires two or more safety devices. (Hint, It reduces time spent on wiring, reduces footprint required inside the enclosure, reduces hardware costs, simplifies maintenance, simplifies documentation and even generates the supporting data for your safety validation report with just a single click of the mouse button.) Making this your complete machine safety solution.

Watch the video

The post Newsletter Volume 21, Issue 6 appeared first on Library.Automationdirect.com.

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Featured Products

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Quick Links to Popular Topics


The post Product Pointers – June 2019 appeared first on Library.Automationdirect.com.

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Most of us are familiar with safety interlock switches that can disable a safety circuit and notify us if a guard has been removed, the gate is open or something has been tampered with. There are many options to chose from including tongue interlock switches, hinge safety interlock switches and non-contact safety switches. Many of these also offer a level of tamper resistance such as the RFID coded non-contact safety switches and coded magnetic non-contact safety switches.

These are all great options if you just need to monitor and de-energize your machinery if something has been removed, opened, or tampered with but what if you also want to lock a guard in place? What if you want to protect a piece of machinery that is still extremely dangerous when de-energized and made accessible to non-authorized personnel? Think of machinery that has sharp blades, something that could still be very hot when de-energized (welders, heaters, etc.), or something that can cause harm or death inside the guarded area such as chemicals, shears, crushers, etc.

The option here is to use a locking safety interlock switch. This will not only provide your E-stop circuit with a safety interlock device that will switch off the safety relay monitoring the E-stop circuit but will also serve as a lock so that only authorized personnel can have access to a guarded area.

AutomationDirect provides two options for locking safety interlock switches. These options are the solenoid locking tongue safety interlock switch and the non-contact magnetic locking RFID switches.

Solenoid Locking Tongue Safety Interlock Switches

Solenoid locking tongue safety interlock switches are similar to the non-locking tongue interlock switches, but maintain a holding force on the key until the solenoid is energized to release. This type of switch unlocks when energized, so something like a PLC will need to be used to energize the solenoid and unlock the switch.

This type of locking switch has anywhere from 1400 to 2000 Newtons of holding force to make sure doors and gates are not easily forced open or guards are forcefully removed.

Solenoid voltages are available in 24VDC, 110VAC, and 230VAC. Solenoid coils are rated so that they can continuously have voltage applied to them.

In the event of a power loss, the switches will need to be manually unlocked, since they are energize to unlock in operation. This is done with a special tamper proof manual release key.

Non-Contact Magnetic Locking RFID Safety Switches

Another option available for use as a locking safety interlock switch is a non-contact magnetic locking RFID switch. These switches still monitor whether a gate is open or closed but since the lock is magnetic,  do not require physical contact with the actuator. They also have more tolerance to misalignment than a locking tongue safety interlock switch.

The holding force on magnetic locking switches is from 600 to 1500 Newtons. Still, a fairly strong holding force, considering that the components of this switch do not require contact with one another.

Tamper resistance is achieved with an RFID coded actuator that mates up with the switch. There are 2 options for the switch/actuator pair. Master-coded and uniquely-coded. With the master-coded the actuator can be used with any other master-coded switch of the same model. This still offers some degree of tamper resistance as an unauthorized person won’t be able to simply use a magnet to “fake out” one of these switches. However, if you want this to be more tamper resistant then uniquely-coded RFID locking safety switches are the option to choose. These require an exact match between the actuator and the switch to work. The drawback to a uniquely-coded RFID switch is that if the actuator is lost or damaged an entire switch pair will need to be replaced.

Locking RFID safety switches are opposite of solenoid locking safety switches in that they are energize to lock instead of energize to unlock. So, in the event of a power loss, the locking RFID safety switches will become unlocked. Certainly, a consideration that needs to be thought about when designing your safety system around your machinery.

Learn more about AutomationDirect’s locking safety interlock switches or any of the other safety products offered.

Click here to learn more about industrial safety.

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Automation Direct Blog by Morgan Collett - 1w ago

When used in electrical power and control circuits, relays allow lower power circuits to operate higher power circuits, while providing isolation.

By Brent Purdy PE, Product Manager, Power & Circuit Protection at AutomationDirect

Relays are a fundamental device for switching an electrical circuit on or off, much like a toggle switch or a limit switch. But a relay is operated based on an electrical control signal, as opposed to a toggle switch that is operated by a human hand, or a limit switch triggered by equipment contact. This blog post covers why relays are used, how they work, the terminology involved, some various relay features and where relays are used.

Why are Relays Used?

The main reason for using relays is so that separate circuits, often operating at higher voltages and currents, can be switched on and off by much lower power control circuits, such as the digital outputs (DOs) of a programmable logic controller (PLC). Small on/off control circuits are effectively amplified to operate large on/off power circuits (Figure 1). The control circuit and the power circuit can be completely different voltages and remain isolated from each other.

Fig. 1: Large relay panels were used to control complex systems like elevators.
Photo Credit: https://commons.wikimedia.org/wiki/File:Panel_Sender_Relays.jpg

A more heavy-duty kind of relay, called a contactor [AD insert web link to “What Is A Contactor?” blog], is used to switch larger loads, such as motors.

Another reason for using relays is to assemble logical circuits for performing other functions. For instance, three relay contacts wired in series produces the result of “Relay1 AND Relay2 AND Relay3”. This result can be used to activate a light or relay when all three relay contacts are closed, for instance. Old elevators and many other types of control panels were effectively programmed by hard-wiring hundreds of relays and timers (Figure 1).

Today, however, most systems like this are automated with PCs or PLCs performing the logic and driving relays interfacing with higher powered equipment. Hence many refer to relays as an interface relays or interposing relays. It is very common to use relays in automation equipment to isolate and protect the digital control system.

How Do Relays Work?
Fig. 2 Electro-mechanical relays use a small electrical control signal to shift contacts operating a separate circuit.

Common relays are electro-mechanical devices (Figure 2). They have an electric solenoid coil which is on the “control” side of the circuit. When this is energized, it moves the mechanical contacts on the “load” side from off to on.

Fig. 3 Small electro-mechanical control relays are often called ice-cube relays.

Another popular style is solid-state relays (Figure 3). These electronic devices use semiconductors to act as contacts. Since there are no physically moving parts, they can operate very quickly.

There are also other specialty types like latching, mercury-switched, reed, and thermal relays.

Electrical Ratings

Relay coils are rated to operate at a certain voltage and will draw a specified current when energized. The pickup voltage is the minimum voltage that will energize the relay, often about 80% of rated voltage. The dropout voltage is the voltage below which an energized relay will de-energize. An energized relay may be called pulled-in. Some relays may be rated with a higher inrush current to energize them, but a lower holding current once pulled-in.

Contacts are also rated for various voltages and currents, and this high-power side must be carefully matched to the load. When contacts are completely isolated from the coils, which is usually the case, they may be called dry contacts. Sometimes the external voltage connected to a dry contact is called a wetting voltage.

AC versus DC Relays

Coils can be AC or DC voltage and must be selected to match the available control circuit voltage. The AC versions are not polarity-sensitive, but the DC versions are, meaning positive and negative must be wired to the right connections. Some AC versions may experience hum or slight noise when energized.

Contacts are also rated for AC or DC voltage and must be selected to match the load. A special concern is that contacts must be able to quench the electrical arc that forms as the contacts are opened. Designers will find it much easier to select relays for switching AC loads than DC. This is because AC power cycles through zero volts and therefore the arc is more readily quenched. Since DC power is at a constant voltage, the arc is more likely to sustain.

Relay contacts have provisions for switching the rated current through millions of operations. Contacts for switching high current use special metals and designs to quench arcing. Contacts for switching very low voltages and currents may be gold-plated. A contact uses some kind of mechanical wiping action to clean itself and protect against corrosion and oxidation.

Relay Contacts

Relay contact connections are exposed on pins or terminals. These terminals may have other designations, but are usually called normally open (N.O.), normally closed (N.C.) and common (C). There are three main forms of relay contacts, which define how the continuity operates at the terminals:

  • Form A, N.O., make contacts,
    when energized, passes power between C and N.O. terminals
  • Form B, N.C., break contacts,
    when energized, interrupts power between C and N.C. terminals
  • Form C, N.O./N.C., changeover or transfer contacts (three terminals),
    when energized, passes power between C and N.O. terminals and interrupts power between C and N.C. terminals
Fig. 4 Solid-state relays have no moving parts and very fast switching times.

Relays can have many different contact arrangements and quantities (Figure 4). The term pole refers to how many isolated contacts a relay has, the most common being single-pole (SP) and double-pole (DP). The term throw indicates if a contact is Form A or B which would be single-throw (ST), or Form C which would be double-throw (DT). The most common configurations one would see on a specification sheet are:

  • SPST
  • SPDT
  • DPST
  • DPDT
  • 3PDT
  • 4PDT

When contacts are first energized closed, they sometimes bounce off and then back on briefly. This is imperceptible under most conditions, but on sensitive control and logic circuits this extra action can cause timing problems. Most contacts are simply on/off, but there are some special contacts called make-before-break and break-before-break that are mechanically arranged to perform those actions.

Special Relays

Basic relays are simply on/off devices, and they fail off to the off position when de-energize. However, a relay may be bistable or latching, which means it alternates when the coil is pulsed and then stays in that position until the next pulse shifts it the other way. These relays fail last in the last position. There are also relays with built-in functions like timer, on-delay, off-delay or pulsing functions. Sometimes these functions are mechanical, but more commonly they employ digital electronics. Some smart relays can perform functions similar to tiny programmable PLCs.

Relay Installation

Relays can have screw terminals, pigtail wires or be soldered into place. Older style relays and higher-current designs may be open with exposed energized parts. Newer and smaller designs are typically touch-safe, so users are less likely to come in contact with energized parts. For most industrial applications, a relay is used with a corresponding socket, which can be screwed into equipment or clipped on to a DIN rail. The socket is hardwired into place, and the relay can be easily removed and replaced. There are many socket sizes and formats, with two popular styles being blade and octal pin. Smaller control relays are often called ice-cube relays due to their size and shape resembling a cube of ice.

Relay Options

Depending on the need, relays are available with many options like:

  • LED/neon indicator light
  • Mechanical indicator flag
  • Mechanical push-to-test button
  • Diode or surge suppression protection
  • Hold down clip for retaining relay in the socket
Design Considerations

Designers need to ensure the relay control circuits are compatible with selected relay coils, which usually means ensuring that a PLC DO has enough current to energize the relay. They also need to make sure that the contacts are suitable for all operating conditions. Relay coils consume power and generate heat in operation. Therefore, designers must calculate the heat load due to relays and allow for it.

Specifying surge suppression is key when interfacing a PLC to a relay. Without suppression, PLC discrete output points on the output card can be damaged by the spike created when the relay deenergizes.

Fig. 5 This diagram shows the connections for several types of relay contacts.

The post What is a Relay? appeared first on Library.Automationdirect.com.

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Automation Direct Blog by Morgan Collett - 2w ago

Human-machine interfaces are available with many hardware and software features. Users should work backwards from the target application to make sure all needs are addressed.

Bill Dehner, a Technical Marketing Manager at AutomationDirect, authored an article for the June 2019 issue of Control Engineering titled Choosing the Right HMI. Here’s a summary, click on the link above for the full text.

End users expect intuitive operator interfaces, and for industrial automation this means using touchscreen human-machine interfaces (HMIs). HMIs are valuable for complementing or superseding the capabilities of switches, buttons and lights in a control panel. The most reliable approach to choosing the right HMI is to examine the specific needs of the target application and work backwards to confirm all necessary options are available.

Weathering the Elements

Any HMI must physically survive where it will be installed by withstanding exposure to water, chemicals, temperatures and other environmental factors. Bill also says another key concern is whether the HMI will be indoors or outdoors.

NEMA and UL ratings commonly are constrained as “indoor use only.” Even the brightest HMIs struggle with sunlight glare outdoors and direct sunlight can cause heat issues. Users should consider locating outdoor HMIs into more protected areas or outfitting them with sunshields.

Some first steps when choosing an HMI are ensuring the environmental ratings are suitable for the service, and that it will physically fit into the available space.

Brightness is a key indicator of ease of use, and backlight life indicates how long the HMI is likely to last.

HMI Physical Display Size and Interface Considerations

Choosing the right display size is a balancing act. Operators and programmers may prefer larger units, while cost or equipment configurations may dictate smaller sizes. HMI hardware product lines with a range of dimensions offer options.

Touchscreen technology is important for industrial applications. Consumer touch devices tend to use capacitive multi-touch, which usually won’t sense gloved fingers and can be affected by water. Industrial HMIs often employ resistive single-touch technology usable with gloved fingers, often preferred for industrial applications.

HMI display size, memory capacity, communication ports and protocols must be selected to match the application.
Don’t Forget the Memory

HMIs are also defined by memory and processor performance. Careful designers will storyboard the anticipated graphics and do some rough estimates of tag counts to ensure they are within limits. Bill points out some other memory considerations.

HMIs with expandable memory or multiple memory sizes may help to remove constraints. It’s also important to remember advanced features such as on-board calculations and trending and recipes will impact HMI performance, so it’s best to use conservative estimates.

Connectivity Concerns

Connectivity is a key factor when selecting an HMI. Most commonly, users will want an Ethernet port so the HMI can communicate with one or more programmable logic controllers (PLCs). Other options are RS232C serial and USB. More recently, another must-have feature is an HDMI output port.

An HDMI connection can drive a second off-board monitor such as a large-format TV located in the plant or facility. An operator can work locally on the HMI display while other operators can see the larger display from a distance.

Make a Software Checklist

HMI programing software features and the development environment require detailed inspection. Operators will want intuitive and easy-to-use graphical objects, while programmers will look for good import/export support and other efficient methods to speed development. Here are the top 10 runtime features users should consider, according to Bill:

  • Basic objects
  • Static library objects
  • Bitmap capability
  • Animated objects
  • Preconfigured complex faceplate objects
  • Advanced trending and recipe objects
  • Security
  • Language switching
  • Alarming
  • Data logging
HMI configuration software should make it easy to create basic graphics, and to implement more advanced features like remote connectivity, data logging and security.

Advanced features like on-board logic, trigger evaluation and event manager functions may be available—and designers should always pre-test more sophisticated functions.

Extending an HMI’s Reach

In recent years, HMIs have moved beyond basic local visualization. Some offer remote access and on-board web servers, extending HMI functionality in new ways to mobile devices.

Hardware and software features deserve close attention by designers as they select an HMI, and these factors should be considered in addition to hardware/software pricing, warranty duration and availability of free support. Obtaining a test sample of the HMI hardware and software is recommended to prove both will meet project needs. Finally, systems offering a simulation mode at low or no cost are a great benefit for testing.

Click here to read more articles related to HMIs.

The post Choosing the Right HMI appeared first on Library.Automationdirect.com.

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