PLC Digital Output Types | Solid State vs Relay
Vložit
- čas přidán 19. 06. 2024
- ▶ C'mon over to realpars.com where you can learn PLC programming faster and easier than you ever thought possible!
=============================
▶ Check out the full blog post over at
realpars.com/plc-output
=============================
⌚Timestamps:
00:00 - Intro
00:52 - Digital vs Analog
01:44 - PLC digital output module types
01:50 - Relay output module
03:09 - Solid-State output modules
03:24 - Transistor output modules
05:00 - Triac output module
05:36 - Output module comparisons
=============================
In this video, we’re going to explore the differences between Solid State and Relay outputs on PLC Digital Output Modules and the pros and cons of each.
The purpose of a PLC Output module is to operate or control a physical device based on field device conditions connected to an input module and decisions made by the PLC program.
Digital or Discrete devices have only 2 possible conditions. These 2 possible conditions could be On or Off, Open or Closed, or Energized or De-energized.
Analog devices are a bit more complicated because they have an infinite number of possible conditions.
A fan is a digital device if it can be turned either on or off.
If the fan can be adjusted for any speed from Off to On, the fan is an analog device because it has an infinite number of possible speeds.
There are 2 types of PLC Digital Output Modules: 1) Relay and 2) Solid State.
1) When PLCs were first introduced, the only outputs were relay type with a separate relay dedicated to each output.
As with any typical relay, the PLC output module had physical coils and relay contacts contained inside.
The contacts were operated by applying a voltage to the relay coil. The contacts were connected to an external supply to turn on or off a discrete device. Not much has changed except today’s modules have miniaturized relays and contacts.
The Allen Bradley 1756-OW16I has 16 individual relay outputs.
We can use one output to operate an AC load and another output to operate a DC load as relay contacts are voltage-independent. That’s one advantage of relay type as solid-state type output modules are not voltage-independent.
Relay Output modules are available with Single Pole Double Throw, or SPDT outputs as well, as seen on the Allen Bradley 1756-OX8I module.
2) Solid-State output modules are often referred to as Switching modules. Output devices are turned on or off by using solid-state devices such as a Bipolar Junction Transistor (BJT) or a Triac.
The Siemens 6ES7322-1BP50-0AA0 (bit.ly/3PLgn2k) is a 64 output Transistor Output Module. As with all transistor output modules, it can control DC loads only.
The Phoenix Contact AXL SE DO 16/1 (bit.ly/3PpeeJC) is a 16 output Transistor Output Module. This module has additional features of Overload and Short Circuit protection of outputs and Peripheral voltage.
3) The Siemens 6ES7522-5FF00-0AB0 (bit.ly/3PELvAo) is an 8 output Triac Output Module.
A Triac output module is capable of controlling AC loads where transistor output modules can control DC loads only. When the PLC signal is applied, the Triac will turn on and provide an alternating current path for the load.
1) Relay
- Relays generally have a higher current rating than transistors, but, as with any mechanical device, it will wear out with time.
- A relay module can operate AC or DC loads, or both.
- Relays provide electrical isolation between the load and the PLC.
- Relays are slow-acting with typical response times of 10 milliseconds or greater.
Closed relay contacts are almost zero ohms thus ensuring no voltage loss.
2) Transistor
- Transistor output modules are for DC applications only.
- Transistors typically cannot switch a large load current as can a relay.
- A transistor is fast because there are no mechanical parts. Their response time is much faster than relays.
- In some transistor modules, there is a leakage current even when turned off.
3) Triac
- A Triac output is used to control AC loads only.
- As with the transistor, a Triac is much faster than a relay.
- Triac outputs are suited to low power AC loads such as lighting, motor starters, and contactors with current ratings of around 1 amp.
=============================
Missed our most recent videos? Watch them here:
realpars.com/pid-tuning/
realpars.com/isa100-wireless
realpars.com/wifi-vs-industri...
=============================
To stay up to date with our last videos, make sure to subscribe to this CZcams channel:
bit.ly/realpars
=============================
TWEET THIS VIDEO ctt.ac/_6AW2
=============================
Follow us on Facebook: / therealpars
Follow us on Twitter: / realpars
Follow us on LinkedIn / realpars
Follow us on Instagram / realparsdotcom
#RealPars #PLC #Transistor
With Realpars, you always learn something new.
That's the goal! :)
What an amazing video!
I am an experienced PLC Programmer but such kind of videos help me develop better understanding of things.
Glad to hear that, happy learning!
Last year i got my bachelor's in mechatronics, robotics and automation. Currently, I am on my master's studies and working in company which main job is industrial automation and machine vision using PLC/Vision System/HMI..etc.
Can't thank you enough for the amount of this quality content.
What an amazing compliment! Thank you, Nikola.
Best of luck on your masters, if you have any questions always feel free to contact us.
Vaughn College In NYC Has Mechatronics Too. How Do You Like The Field?
This was very helpful and a learned a bit. I remember on a huge project for a PLC Upgrade at a Power Plant in the South West about a year ago we used some new type Relays. I'd never seen them before and was like maybe a dozen installed. They were from Rockwell and looked like what is Transistors with LED Lights. At first, I had no idea what they were, but my senior said they were Relays. I said Ok and that was it. It now dawned on me they were like Solid State Transistor Relays, I just never knew. Good Stuff RealPars!
Thanks for sharing that, Ardent! Glad to hear that it was helpful
Excellent video ! As usual, very well explained and entertaining. I'm always looking out for new content from you !
That's amazing! Glad to hear that.
Old school relays are still pretty dominant at the last plant I worked at.
Was s great video! This information will be very useful in my job!
That's great to hear! Happy learning.
Great video, thanks
Very clear explanation thanks you so much
You're very welcome!
Thank you for the informative and succinct video!!!
You're very welcome, Andrey!
Really very instructive videos as always! Thanks for sharing
Glad you like them!
I learnt a lot from your videos . I am just starting my working career . It's very useful.
That's great to hear, Dulal! Keep up the learning curve and best of luck in your career!
Very good, Thank You very much
You're very welcome!
Damn I entirely watched ur all awesome uploads sir.. really friendly tutorial video easily to understand.. keep up the good work sir. More subscribers to come..
Thanks a lot, we're glad to hear that!
Very well done video!
Thank you, Diana!
Best and the Beast of the field
thank you for this video.
You're very welcome! Let us know of any questions! :)
@@realpars Thank you so much. actually I have been digging more of robot related videos from you. haha
You're very welcome! We have some videos on servo motors but I will let the content tean know about your request! ;)
Thank you so much !
Our pleasure! Happy learning.
Thanks for the video. I almost exclusively use relay outputs.
Our pleasure!
Thank you very much. I would like to make video about the relations between plc and HMI, and between inverter and HMI
Hi Ala!
Thanks for your comment and your suggestion. I will pass this on to our course developers!
Thanks for sharing and happy learning!
It's really good.....
Great video thanks! I am new to PLC. Is it normal to receive energy from the outputs when common is energized?
No. Most digital outputs are sourcing type.
Very good. Thanks 🙏🙏🙏
Glad to hear that!
Good learning.
Great!
Thank you this video
You're very welcome!
Very useful 👌
Glad to hear that!
Awesome..
Excellent sir
Thank you very much!
REALPARS IS THE BEST OF THE BEST.
Amazing! Thanks for sharing.
Great video
Thanks for your support!
nice explanation
Thank you, Muhammad!
Thnx sir u really help me cuz am just beginner 🙏please can u tell me how i connect sinking module and sourcing module
Thanks for your comment, Redouane!
I will pass this on to our course developers as a topic suggestion. Thanks for sharing and happy learning!
helps thx
Possible practical training on DO 8*REL SM 322 230V
I only source SS output modules. They are much less expensive and seem to be easier to source. This decision is easy by using slim 6mm relays in conjunction with SS output module. The slim relays allow for different power feeds, custom interlocks, take up little real estate, and are inexpensive. The combined cost of both the SS output module and the slim relays is still less than a relay output module alone. Another benefit is the isolation of the controller from the field devices.
From my experience, working at a machine integrator as a controls programmer, most of this is good information but largely obsolete for machine design. For any AC load, a contactor or VFD/Line reactor will be used regardless because of the limitations on switching such high currents and also because replacing the components if they become damaged is typically cheaper and less detrimental to machine downtime than replacing the PLC module. This is still good information to be aware of but it is not strictly required, sinking and sourcing are more important concepts in my opinion.
Hi Shearzy. Thanks for your feedback. You are correct of course. No PLC output is capable of operating typical AC loads in a plant and some type of interposing device as you described is required. We touched on the current limitations of PLC digital output modules in the video. As you say, sinking and sourcing are very important concepts. We’ve got more videos that will be released soon dedicated to sinking and sourcing PLC I/O modules and active field devices. Plus, we’ve got more videos soon-to-be released on motor starter types and controls. Stay Tuned!
In Siemens plc S7 -1500 and ET200S which type of output module used??
Hi Sumaiya! As with all PLC's, both types of modules are used depending upon the application. Most PLC vendors have expansion modules to work with a variety of loads and voltage supplies. You can buy modules to work with AC or DC loads. You can but solid-state or dry relay type. Vendors have modules available with 4,8,16 or more outputs as well! There are too many different options available for Siemens PLC's to list here. For example, if you do a web search for S7-1500 series modules, you'll be surprised at how many options are available.
I only use BJT modules to operate external triacs or relays. If an external relay fails, I can replace it cheaply and in seconds, as opposed to an internal relay that's part of a multi channel device.
Are the transistor outputs isolated from the control circuit within the PLC?
Yes, in many cases they are. At 4:20 in the video, the output shown is an optically-isolated output channel. This arrangement is desirable for all PLC DC output cards. For AC circuits, triacs are used, which create independent 120 VAC circuits with each device. These devices are very robust and although not isolated from the PLC driving voltage upon a failure.
i can't say thank you enough
You're more than welcome!
This topic has been always confusing me. Not any more of course.
Thx a bunch
Glad to hear that!
Looks like the good old relay is still standing tall.
They're simple and almost everyone is familiar with them.
i would like to see video about long distance wiring, interfaces, setup. If you have already and i've missed please can you reply with a link.
Hi Tomi,
Thanks for your topic suggestion! I will happily go ahead and pass this on to our course developers.
Thanks again for sharing and happy learning!
Please upload a video about ' WAGO' profibus module 750-333
Hey!
Thanks for your comment and your suggestion. I will pass this on to our course developers!
Thanks for sharing and happy learning!
Can we use 1plc output to another plc input without touching plc1 program.. Just by using hardware?
Yes, provided the input and output card circuits are compatible (both 24VDC, on the same power supply circuit, etc., for example). I do this all the time to provide a level of simulation before the installation of the system in the field. Many times, this is also the best way to provide a critical signal from one PLC to another, especially for shutdown and status signals, as opposed to software transfer of data, where the data may be lost due to network or other communication issues.
How come you never mentioned the flyback diode required in parallel with the relay?
Hi @RSuarez66. Thanks for reaching out. Your question is a good one. A flyback, reverse-biased diode isn't always required in parallel with a relay coil. You'll see lots of relays that don't have flyback diodes. Generally speaking, the flyback diode eliminates possible high voltage sparks when the relay coil is de-energized by attempting to remove its energizing current instantly. These high-voltage sparks can cause damage to sensitive electronics anywhere near the relay, and that's why you see a flyback diode. You'll also see them in environments where sparks could cause fires or explosions, such as on fracking equipment. So, in a nutshell - no sensitive electronics nearby, no explosion hazard, no flyback diode. I hope that answers your question!
What about PWM?
Hi Martin. Thanks for your question. Yes indeed. Many vendors offer both sinking and sourcing PWM output modules. MOSFETs are quite popular as the internal switching device.
This appears to miss the 2 most important distinctions between relays and solid state. 1) in a short circuit condition, the solid state device will fail before the fuse, while the relay may survive depending on available energy. 2) A relay can fail with welded contacts, but this is less likely than failing open where energy is limited. Solid state devices fail short circuit exclusively, unless a great amount of energy is available. Solid state devices are far more susceptible to short voltage excursions causing failure . I'm personally an electronics geek at heart and am grossed out by mechanical relays, but they have significant advantages in the industrial world.
Hi Paul. Thanks for your feedback. We certainly agree that solid state devices are far more "delicate" than good old fashion relays. As you say and as we pointed out as well, mechanical type failures such as welded contacts are problematic with relays. Even with all its inherent frailties, the mechanical relay is going to be with us for many years to come.
Thank you so much!
Happy learning!
@@realpars ❤️