PLC and Terminal block and Sensor wiring selection

[DamianInRochester]

So then I got a pretty good deal? I mean, they're used, but at $5 each (2 IDC24 and 2 ODC24), including the junction box is a good deal, no?

So are these to be used as input/output modules for micro-controller-type applications only?

I have actually considered buying a bunch of those same ones you did. They have been on Ebay for many years. Most of my customers prefer new so I never really bothered.

But yes, I don't think that is a bad deal. I have used many of them, and for a long time and have never seen one fail.

As far as use, I use them anytime I want to isolate two systems electrically, especially in systems that may cycle that communication at 1Hz or faster. Relays always eventually fail but these can go on practically indefinitely.

Back in the day we used to use a lot of the Opto22 PCB style modules with the 4 pole and 8 poles plug in boards. They were a pain in the neck to mount (Really long 4-40 screws if memory serves correct) and they took up a lot of space. Some would get the style with the ribbon cable header and then try to terminate the 28/30awg (or whatever the heck microscopic wire size is used on them and they were always te source of a bad connection.

These just snap right on the DIN and also have the handy little cube fuse and LED indication right on top of the device.

 

[SergioB]

As far as use, I use them anytime I want to isolate two systems electrically, especially in systems that may cycle that communication at 1Hz or faster.

A lot of great info... however... must-ask-more...

Sorry, beginner over here. So these "input/output" modules are basically solid-state relays that I can use with my PLC to turn DC devices on and off? and if this is the case, is the input/output designation relevant when used in plc application?

 

[DamianInRochester]

A lot of great info... however... must-ask-more...

Sorry, beginner over here. So these "input/output" modules are basically solid-state relays that I can use with my PLC to turn DC devices on and off? and if this is the case, is the input/output designation relevant when used in plc application?

They are not only solid state, but are opto-couplers. The red ones in the Picture are probably DR-ODC24 which are handy for interfacing 5 volt systems to 24volt system, or 24vdc system to other 24vdc systems. But there are different models for different things. DR-OAC modules are handy for interfacing 5v and 24V logic to 115vac logic (and maybe even 230vac but I don't remeber).

The biggest reason Opto relays became popular back then was because there was a lot of devices (like servos/stepper, function boards, controllers, etc) where the manufacturer only supported 5volt logic. Since most industrial DC IO was usually 24VDC levels relays were often needed to get things integrated. Over the years the manufacturers wised up and starting making their I/O support 24VDC logic levels because of the noise immunity and the lack of necessity for ....... well...... all these opto-relays.

I rarely see industrial devices anymore that can't support 24VDC logic levels.

 

[SergioB]

Great!!! Thanks a lot for the info!

I was thinking about using these relays to switch on/off multiple analog devices. You see, I need to receive data from about 16 analog input devices and control around 8 analog output devices. I only have a combination input/output 4 channel analog card. This seems like a cheaper way of doing it for the time being, while I can afford a 16 channel analog input card and an 8 channel analog output card.

What do you think about this idea? Be gentle...

 

[DamianInRochester]

Great!!! Thanks a lot for the info!

I was thinking about using these relays to switch on/off multiple analog devices. You see, I need to receive data from about 16 analog input devices and control around 8 analog output devices. I only have a combination input/output 4 channel analog card. This seems like a cheaper way of doing it for the time being, while I can afford a 16 channel analog input card and an 8 channel analog output card.

What do you think about this idea? Be gentle...

Not knowing the details of your application, as always the devil is always in the details.

I would not consider it personally. It would cost me more in engineering and labor to implement all those relays. Then it also adds additional points of failure. Not to mention that you still have to switch the relay coils with something (another output card?) and invest time in programming it.

The solid state devices we have been discussing would not be appropriate for this. Reed relays with a low resistance contact would help minimize signal attenuation.

Then comes the fun part. Conversion times, filtering, sampling rates, etc. How quick do you need the data? How fast are your analog inputs at responding to a change in signal? How stable are your signals? You could easily spend hours upon hours just working all these details out.

And there are probably even more negatives that I can't think of off the top of my head.

I have actually done what you are proposing long ago. It was a high limit temp monitor that required very slow monitoring and relatively crude accuracy. It worked. It probably still is working where ever it ended up. But I ended up feeling it was more trouble than it was worth.

 

[SergioB]

Then comes the fun part. Conversion times, filtering, sampling rates, etc. How quick do you need the data? How fast are your analog inputs at responding to a change in signal? How stable are your signals? You could easily spend hours upon hours just working all these details out.

My application also requires slow monitoring and crude accuracy. I would only set it up this way temporarily while I'm able to get additional hardware.

Not scared necessarily with setting up the logic, since my background is in software development so I'm used to working out pretty complex algorithms. I'm more scared about electrical concepts, such as "signal attenuation" for instance. I guess I need to finish reading up the Lessons in Electric Circuits PDFs I downloaded, he he.

By the way, I do have spare 16-channel DC input/output AB cards. Does it become an issue that these cards also use solid state relays?

Thanks!

 

[DamianInRochester]

Sergio This link is a good read for multiplexing analog signals. They are looking at it more from an electronics end, but there is still a lot of good info to absorb.

http://www.mccdaq.com/PDFs/specs/Multiplexing-and-Sampling.pdf

Not sure what you mean by "Does it become an isse that these cards also use solid state relays".

 

[SergioB]

Not sure what you mean by "Does it become an isse that these cards also use solid state relays".

Thanks for the link. It looks like it's going to be very helpful for what I'm trying to do.

I said that based on your previous post (ie The solid state devices we have been discussing would not be appropriate for this). I thought you were talking about a general issue doing what I was intending to do with SSRs.

 

[DamianInRochester]

Here is the spec sheet for the DR-ODC24 relays.

http://www.crydom.com/en/products/catalog/dr_output_modules.pdf

Look at the specs on the ouput. You will notice a minimum line voltage of 3.0VDC. You will also notice a minimum on current of 10mA. And then an ON state voltage of 1.6 volts (to bias the junction). If your working with 0 or 4-20mA devices you will lose half your signal just turning the device on. And since that is the threshold point it will also be a bit non-linear in this region which will distort your signal. If you are going 0 to 10VDC (obviously you can't go bipolar because of the internal diode) the you have to drive enough current again to turn the device on. Most voltage analog inputs are very high impedence and will draw very little current. Even if you did get enough to turn it on, you still then have to account for the 1.6V. Neither of these is an issue with the reed relay.

This isn't to say that there are not solid state devices appropriate for switching analog signals. It is done all the time. It is just that this device doesn't fall into that category.

 

[SergioB]

Most voltage analog inputs are very high impedence and will draw very little current. Even if you did get enough to turn it on, you still then have to account for the 1.6V. Neither of these is an issue with the reed relay.

Thanks for all the good tips. I keep learning a lot of things I hadn't considered.

Now, since the whole point of this is to save some money, how about using one of those Wago mounting carriers with miniature switching relays (shown on page 29 of wago catalog)? Do these require a special interface to energize them or do they work as regular relays?

Specifically, looking at a WAGO 810-288/016 Relay module with 11 places 24V DC relays input output card on eBay. Snapshot shown below:

Looks like a great deal, if it can work with my application. Could you recommend a few options?

Thanks!

 

[The Plc Kid]

Buy the analog card for the number of channels you need and be done with it so the maintenance guy of the future is not cussing you at 2:00 am on a call in.

 

[SergioB]

Buy the analog card for the number of channels you need and be done with it so the maintenance guy of the future is not cussing you at 2:00 am on a call in.

Thanks for the recommendation but I would never consider doing this for a client. This is not a commercial project, it's a personal project and a learning one at that.

Besides being cheaper to implement, it is an opportunity to learn with a more challenging design. Besides, I will replace the home-made multiplexer with a single analog cards within a couple of months.

 

[DamianInRochester]

Thanks for all the good tips. I keep learning a lot of things I hadn't considered.

Now, since the whole point of this is to save some money, how about using one of those Wago mounting carriers with miniature switching relays (shown on page 29 of wago catalog)? Do these require a special interface to energize them or do they work as regular relays?

Specifically, looking at a WAGO 810-288/016 Relay module with 11 places 24V DC relays input output card on eBay. Snapshot shown below:



Looks like a great deal, if it can work with my application. Could you recommend a few options?

Thanks!

If this is more of a science project, why not just get a real multiplexer?

http://www.jameco.com/webapp/wcs/st...001&categoryName=cat_1015&subCategoryName=ICs %26 Semiconductors%20%2F%20Analog/Linear%20%2F%20Multiplexer or Switch&category=101552

The above is all one big link, you will have to copy it spaces and all even though this site choked at the first space.

As far as whether the above relays will work, I encourage you to look at the specs and come up with your own conclusion. What is the coil voltage? How many signals are you multi-plexing into how many inputs? What I/O cards do you have available to drive the outputs?

 

[SergioB]

If this is more of a science project, why not just get a real multiplexer?

As far as whether the above relays will work, I encourage you to look at the specs and come up with your own conclusion. What is the coil voltage? How many signals are you multi-plexing into how many inputs? What I/O cards do you have available to drive the outputs?

It is not a science project, but a homemade climate and ambient control (humidity, heat, light, co2, etc). Don't think of it as whether the project makes sense, but think of it as me having a lot of time and access some PLC hardware and relays to play with where the main purpose is to help me learn about PLCs.

By the way, I looked for specs on this relay module, but found none. Come to think of it, this seems like an older model, and this is probably the reason for lack of specs out there. I'll look for something similar instead.

Thanks!

 

[DamianInRochester]

I mentioned getting a mulitplever instead of a relay bank simply because it would be cheaper. The implementation as far as the PLC goes would not be much different than using regular relays. Instead of selecting the relays one by one, you would instead select the relays with binary coded bits. So it is probably an even better educational experience.