First PLC, requesting second set of eyes

stoubia

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S
Join Date
Apr 2014
Location
Southern California
Posts
2
Hello all,

I am putting together my first PLC/automation design at a company I recently started working for. I'm a EE (just graduated, little experience) so I have some knowledge of electronics, but I'm more experienced with microcontrollers and haven't touched PLCs before. The machine itself is very simple and straightforward for the most part, but I have some questions when it comes to the I guess you could call common industry practices (fuses and circuit breakers, safety relays, emergency stop switch, terminal blocks etc.) I'll give an overview of my project below and try and give specific questions, hopefully somebody with plenty of experience can help me out here.

Function
Control a hydraulic cylinder for a press fit assembly operation

Main components

CLICK PLC :
  • CPU: C0-02DR-D link
  • 8 Relay In/Out: C0-08TR link
  • 8 DC Input: c0-08ND3 link
  • 24V, 1.3A PSU: C0-01AC link

Hydraulic Components:
1 Hydraulic power unit (Parker-Hannifin, 10A @ 120VAC, similar model: here )
1 3 position - 4 way solenoid (built into hydraulic power unit, solenoid A and B controlled by 120VAC. 1.90A In Rush, 0.42A Holding, 21W. 3 positions are forward, back, and crossfeed/cylinder lock whatever)
1 hydraulic cylinder (double acting)
1 pressure transmitter (noshok, 4-20 mA out, 24VDC, attached to supply port on cylinder to measure force being applied)

Switches, indicators, safety relays:
1 magnetic safety switch (door safety lock, supplier)
1 LED tower lights (already have them, going to use them even if there was something simpler. link)
2 momentary pushbuttons w/ 1 N.O. contact block each (two handed activation for hydraulic link)
1 twist-release pushbutton w/ N.C. contact block (for e-stop)
1 Illuminated 2-position N.O. selector switch (probably will use for on/off)
1 2-position key-operated N.O. selector switch (might use for some safety precaution instead/in addition to other on/off selector switch)
1 Safety Relay, 110 VAC, 3 N.O.+1 N.C contact, 1 channel (probably for E-stop, link)
1 Safety Relay, 24VDC, 3 N.O.+1 N.C., 2-channel (for mag safety gate switch)
2 momentary limit switches with roller (stroke min and max of hydraulic cylinder)

Operation Sequence
  1. Operator loads part to be press fit
  2. operator closes door
  3. operator presses both buttons to initiate pressing
  4. hydraulic cylinder powers on and extends until pressure reading reaches desired value/max stroke limit reached
  5. cylinder retracts (only while door remains closed)
  6. part is unloaded


Questions

1. How should I configure my safety relays and E-stop? I want to cut the power to the hydraulic pump when the door is open, when the start buttons are not pressed, and when the E-Stop is activated. The two safety relays I listed above are what I have on hand, I can add or subtract anything at this point.
1a. Is the best method of isolating the AC voltage to a motor to put a switch/relay on the load line?
1b. Each contact on the relay is rated for 5A (there are 3 NO contacts). The hydraulic pump is rated at 10 amps. Is it OK to split the load over the 3 contacts (assuming I only need to switch the load line), or do I need a relay with a higher rating?
1c. Could somebody recommend surge protection circuitry? The motor is definitely the heaviest load I have in this system, I will need something on the AC line I imagine.
1d. One of the relays I have has 2 channels, the other has 1. Should I use both relays, or just the 2 channel? Im using an encoded magnet switch and an emergency stop switch, but what about the on/off switch? Or would it ever be necessary to put a PLC output on one of the safety relay channels?

2. Input AC Voltage: there are 3 wires coming into the system (L, N, G). I understand I should put a fuse (or breaker?) on the incoming line.
2a. Is it only required on one of the lines (L)? or do I also need one on the neutral line.
2b. 120VAC is also needed to power the hydraulic power unit, the 2 hydraulic solenoids, and the stack lights. Do I need anything special to isolate the different modules?
2c. related to 2b, how do I size my fusus/breakers appropriately


3. PLC PSU:
3a. Do I need something on my +24V line between the PSU and the PLC?
3b. I have a second identical +24V PSU, is it recommended that I use that for non-PLC items to keep them isolated? (pushbuttons, safety switch)

4. Terminal Blocks: What are they, why would I want to use them?

5. Hydraulic Solenoids:
5a. What type of protection circuitry should I consider for these? Each of the 2 coils is rated at 1.90A inrush and .42A holding.
5b. The current rating seems within the ratings for my PLC's built in relay, so it should be fine to control it directly from the PLC (no external relay), right? I imagine the connection would be simply PLC out -> fuse/breaker -> solenoid.

6. The stacklight unit I have has a built in wiring, I was able to wire the whole thing to my relay I/O board to control the 3 lights, 1 buzzer, and a flashing mode for all 4 (8 lines in total). Wiring schematic found on the amazon page. I probed at it a little with a voltmeter, it seems like the common lines provide something like 50 VAC.
Should I bother putting any circuit protection on this device?

7. Any tips and tricks on putting together the enclosure? I want to make this thing look nice and organized. I was probably going to pick a box off of automation direct . Everything is getting mounted on the DIN Rails. I figure with the correct combination of terminal blocks, circuit breakers, cable management tricks etc. it will look very nice. Its a very simple system anyway, so it's good to start small.




Thanks for giving me your time, I appreciate any help I can get. I'm going to put together some block diagrams for various sections of the system and try and post them soon to try and show what I've got so far.
 
Find a local Systems Integrator that you can work with and learn as much as possible from them while doing this project before you attempt one on your own. That's my best advice, based upon your questions.
 
You may have scared everyone with some of your question like.
4. Terminal Blocks: What are they, why would I want to use them?

Realistically if you are unaware of how you terminate the wires you are going to run, whether control or power, I would suggest to take Bit_Buckets advice, as you can endanger peoples lives with the equipment you are wiring up.
 
stoubia said:
Hello all,

I am putting together my first PLC/automation design at a company I recently started working for. I'm a EE (just graduated, little experience) so I have some knowledge of electronics, but I'm more experienced with microcontrollers and haven't touched PLCs before. The machine itself is very simple and straightforward for the most part, but I have some questions when it comes to the I guess you could call common industry practices (fuses and circuit breakers, safety relays, emergency stop switch, terminal blocks etc.) I'll give an overview of my project below and try and give specific questions, hopefully somebody with plenty of experience can help me out here.

Function
Control a hydraulic cylinder for a press fit assembly operation

---

Questions

1. How should I configure my safety relays and E-stop? I want to cut the power to the hydraulic pump when the door is open, when the start buttons are not pressed, and when the E-Stop is activated. The two safety relays I listed above are what I have on hand, I can add or subtract anything at this point.
Click to expand...

You need a safety risk assessment to know for sure. Generally, your two hand operation is a hardwired two hand safety relay, or a safety relay that can be configured as one, also called anti-tiedown relay. Typically, 2 channel switches and safety inputs are used for any and all modern designs. I am a big fan of the RFID based Siphacode switches if you have a bunch of covers or doors to monitor and they get opened a lot.

stoubia said:
1a. Is the best method of isolating the AC voltage to a motor to put a switch/relay on the load line?
1b. Each contact on the relay is rated for 5A (there are 3 NO contacts). The hydraulic pump is rated at 10 amps. Is it OK to split the load over the 3 contacts (assuming I only need to switch the load line), or do I need a relay with a higher rating?
1c. Could somebody recommend surge protection circuitry? The motor is definitely the heaviest load I have in this system, I will need something on the AC line I imagine.
Click to expand...

You need a motor protective circuit designed for a motor starter, I normally use a 30amp 4 pole or 3 pole IEC style 3 phase contactor for even single phase motors, and you can add the overload block for your make and model of favorite small contactor. I always go as big as the frame size allows for the contact ratings for motor loads when the cost is not that different from a 15amp rating. RTFM for the OL block to make sure it will work with a single phase load.

stoubia said:
1d. One of the relays I have has 2 channels, the other has 1. Should I use both relays, or just the 2 channel? Im using an encoded magnet switch and an emergency stop switch, but what about the on/off switch? Or would it ever be necessary to put a PLC output on one of the safety relay channels?
Click to expand...
It is common to run a fused power source through the redundant safety contacts of the safety relay before it supplies voltage to PLC output modules or other circuits that may be unsafe if energized.

It is common to wire two contacts from each E-Stop pushbutton in series with your other guard switches to the input channels of the safety relay. The relay for the two hand control would normally be wired to begin the cycle with a contact to the PLC and to supply and interrupt power to controls that operate the pump/solenoids.

stoubia said:
2. Input AC Voltage: there are 3 wires coming into the system (L, N, G). I understand I should put a fuse (or breaker?) on the incoming line.
2a. Is it only required on one of the lines (L)? or do I also need one on the neutral line.
2b. 120VAC is also needed to power the hydraulic power unit, the 2 hydraulic solenoids, and the stack lights. Do I need anything special to isolate the different modules?
2c. related to 2b, how do I size my fusus/breakers appropriately


3. PLC PSU:
3a. Do I need something on my +24V line between the PSU and the PLC?
3b. I have a second identical +24V PSU, is it recommended that I use that for non-PLC items to keep them isolated? (pushbuttons, safety switch)

4. Terminal Blocks: What are they, why would I want to use them?

5. Hydraulic Solenoids:
5a. What type of protection circuitry should I consider for these? Each of the 2 coils is rated at 1.90A inrush and .42A holding.
5b. The current rating seems within the ratings for my PLC's built in relay, so it should be fine to control it directly from the PLC (no external relay), right? I imagine the connection would be simply PLC out -> fuse/breaker -> solenoid.

6. The stacklight unit I have has a built in wiring, I was able to wire the whole thing to my relay I/O board to control the 3 lights, 1 buzzer, and a flashing mode for all 4 (8 lines in total). Wiring schematic found on the amazon page. I probed at it a little with a voltmeter, it seems like the common lines provide something like 50 VAC.
Should I bother putting any circuit protection on this device?

7. Any tips and tricks on putting together the enclosure? I want to make this thing look nice and organized. I was probably going to pick a box off of automation direct . Everything is getting mounted on the DIN Rails. I figure with the correct combination of terminal blocks, circuit breakers, cable management tricks etc. it will look very nice. Its a very simple system anyway, so it's good to start small.




Thanks for giving me your time, I appreciate any help I can get. I'm going to put together some block diagrams for various sections of the system and try and post them soon to try and show what I've got so far.
Click to expand...

Oh wow, you have way more questions than I have energy right now... but there is a start...you definitely need experienced in-person help with this, don't learn all this at once the hard way.
 
Stoubia,

If you have just graduated and joined a company, then you should have a mentor to guide you through the elements of your project.
Has your company already got similar control circuits that you can view the drawings and the panel to get an idea of expected standards? Different companies (and countries) have different expectations when it comes to panel design, although the principles are the same.
Without answering your questions above, I suggest a step back and start from basic theory and practice, so that you are not trying to run before you can walk......
 
1 Hydraulic power unit (Parker-Hannifin, 10A @ 120VAC, similar model: here )
Click to expand...
No that Parker-Hannifin Hydraulic Power Unit in your link is NOT 120 volts, but instead 208-230/460 volts with 3-phase power. Read its specifications. You can operate it on 3-phase power at 208 volts, 240 volts, or 460 volts, but NOT 120 volts 1-phase power- UNLESS you swap out the motor. You will need a 3-phase motor starter of some type, maybe with a 24 volt DC control coil.
1a. Is the best method of isolating the AC voltage to a motor to put a switch/relay on the load line?
Click to expand...
Use your Safety Relay to break the power to the motor starter control coil. Also you will need to use your safety relay to block the power going to your cylinder solenoid valves.

3. PLC PSU:
3a. Do I need something on my +24V line between the PSU and the PLC?
Click to expand...
Yes, fuse or circuit breaker. Also you will need to run your 24 volt power to several terminal blocks, so you can split it to all the circuits that need 24 volt DC power.
3b. I have a second identical +24V PSU, is it recommended that I use that for non-PLC items to keep them isolated? (pushbuttons, safety switch)
Click to expand...
Probably not for this small control panel.
Should I bother putting any circuit protection on this device?
Click to expand...
Every electrical device should have a fuse or circuit breaker. In your case for your first project, yes you should add a 0.5 Amp 120 volt fuse inline on the supply end of the black "continuous common wire" shown in the American Stack Light diagram. This stack light is rated for 8 watts at 120 volts = 0.06 amps, but a short circuit with no fuse could pull 20 amps. If the 120 volt power to the stacklight comes from a separate circuit, and you run it back to relays in your control panel, then you will need to label your panel with a warning sticker that "This panel has more than one power supply", or similar, and list the location of all breakers to kill all the power.
I figure with the correct combination of terminal blocks, circuit breakers, cable management tricks etc. it will look very nice. Its a very simple system anyway, so it's good to start small.
Click to expand...
It will look nice if you plan ahead and leave enough room to get your hands into the small places to connect your wires. Lay out your parts and mark the mounting spots, then double-check everything before you drill any holes. Plan carefully for the wires that go from your back panel over to your switches and indicators on the back of the panel door. Leave room for the bundle of wires to have some slack so that it will twist when you shut the door (instead of bending).
 
Last edited:
First let me say thank you everybody for all your input, you are all amazing for taking the time to help me out!

I've finished my preliminary wiring diagram (attached), I'm hoping (and think) that I'm close on this one. I think most of the 'blanks' left in this schematic have to do mostly with the fuses/breakers. I also feel theres a few choices as for the 24VDC/120VAC scheme, but as for if one way is more right that the other, I don't know. Looks like it should work fine to me. As for the schematic itself, it's probably not 100% to wiring diagram conventions, but I'm learning so feedback on that would also be appreciated.

I think once I have the rough wiring diagram down, I can pick out the final components list, then make a more complete detailed wiring schematic. Then is the part where I do the physical enclosure layout and determine my wiring routes. Correct me if my sequence of events is out of order or if I'm missing something.

Just to share, these are some of the larger more immediate items on my 'to-do' list of info I'm missing thats holding me back from the next step (the known unknowns):
  • Fuses and Breakers: sizing, type and placement. Mostly type and placement.
  • Hydraulic Solenoids: circuit protection?
  • Motor starter relay: make, model, protection accessories
  • Safety Relays: detailed wiring.

and an incomplete list of tasks to come later:
  • Naming, numbering, wiring, labeling conventions
  • Enclosures: ?
  • PLC programming
  • Terminal blocks
  • Wire management outside the enclosure (button panel, door switch, hydraulic power)
  • documentation?

Now, to address your advise and concerns:

Bit_Bucket_07 said:
Find a local Systems Integrator that you can work with and learn as much as possible from them while doing this project before you attempt one on your own. That's my best advice, based upon your questions.
Click to expand...

duckman said:
Realistically if you are unaware of how you terminate the wires you are going to run, whether control or power, I would suggest to take Bit_Buckets advice, as you can endanger peoples lives with the equipment you are wiring up.
Click to expand...

Bit_Bucket (and duckman), I agree this is the best most practical advice, but I'm going to keep working on it until I either stop making continual progress or I am completely stuck. But please rest assured, I don't intend on building the thing unless I have completely verified the design for safety. If I can't figure it out, then yeah I'm going to go talk to one of the local integrators we have around here.

JohnCalderwood said:
Stoubia,

If you have just graduated and joined a company, then you should have a mentor to guide you through the elements of your project.
Has your company already got similar control circuits that you can view the drawings and the panel to get an idea of expected standards? Different companies (and countries) have different expectations when it comes to panel design, although the principles are the same.
Without answering your questions above, I suggest a step back and start from basic theory and practice, so that you are not trying to run before you can walk......
Click to expand...

Small company, is primarily a machine shop, we are building this machine to assemble one of our products so we are just starting to dip our toes into automation. So no, there's no similar control circuits designed in house, but plenty of CNC machinery around. The only expectation coming out of this is that it works and it is safe, but as for the tidiness of the enclosure, I'm probably the only one here that cares about that. I spend a little bit each day looking for good resources for some basic theory, I find some online pages, some videos, etc. I always find it best to have a specific application in mind when learning something new, so I'm really learning a lot every day I sit down and work on this design. I literally started this design last Tuesday (4/22), so I haven't been working on it very long, and it's not the only thing I work on all day either.
Any good go to resources you might know off the top of your head would be great, the more the better. Thanks for your input!

OkiePC said:
You need a safety risk assessment to know for sure. Generally, your two hand operation is a hardwired two hand safety relay, or a safety relay that can be configured as one, also called anti-tiedown relay. Typically, 2 channel switches and safety inputs are used for any and all modern designs. I am a big fan of the RFID based Siphacode switches if you have a bunch of covers or doors to monitor and they get opened a lot.
Click to expand...

I hope my attached schematic shows some promise. I'll have to determine the detailed wiring once I have the final components selected. I was probing at the one safety relay I already have trying to characterize it, but was having some difficulty with it. Might have accidentally destroyed it from thinking it was a 120VAC, when in fact it was a 24V (doh!).

I'll have to keep those Siphacode switches in mind for the next project, I've already got the coded magnet switch but the Siphacodes are well priced.

OkiePC said:
You need a motor protective circuit designed for a motor starter, I normally use a 30amp 4 pole or 3 pole IEC style 3 phase contactor for even single phase motors, and you can add the overload block for your make and model of favorite small contactor. I always go as big as the frame size allows for the contact ratings for motor loads when the cost is not that different from a 15amp rating. RTFM for the OL block to make sure it will work with a single phase load.
Click to expand...

Motor starters/contactors. Came across these yesterday after making my first post. Still need to do a little research in this area. Trying to pick something from AutomationDirect's motor controller section (keeping it simple, sticking with one supplier right now). I was digging through one of the spec sheets on one of the contactors on there and saw that there were many accessories and configurations to throw in the mix. Still plenty of details to figure out here, but I haven't looked into it yet since I've been working on the wiring diagram.

OkiePC said:
Oh wow, you have way more questions than I have energy right now... but there is a start...you definitely need experienced in-person help with this, don't learn all this at once the hard way.
Click to expand...

Hahah yeah I let it all out. But seriously, thanks for the advice, didn't expect anybody to answer as much as you did anyway! And I like the hard way, I'm stubborn like that. Don't worry, I'll get help when it comes to that.


Lancie1 said:
No that Parker-Hannifin Hydraulic Power Unit in your link is NOT 120 volts, but instead 208-230/460 volts with 3-phase power. Read its specifications. You can operate it on 3-phase power at 208 volts, 240 volts, or 460 volts, but NOT 120 volts 1-phase power- UNLESS you swap out the motor. You will need a 3-phase motor starter of some type, maybe with a 24 volt DC control coil.
Click to expand...

Sorry for the confusion, the McMaster link I gave is for a different configuration. We ordered directly from parker through an integrator for our specific config, I assure you all the specs I gave in the first post are accurate.

As for the motor starter, I'm still figuring out the details but I'm getting closer. The way my wiring scheme is currently configured I'll use a motor starter with a 120VAC control coil so I can run it off the same relay outputs as my solenoids. This could all change if it ends up being a better idea to run the hydraulic solenoids from an external relay as well, in that case I'd still spec the motor starter to match those relays.


Lancie1 said:
Yes, fuse or circuit breaker. Also you will need to run your 24 volt power to several terminal blocks, so you can split it to all the circuits that need 24 volt DC power.
Click to expand...

Picking fuses and/or circuit breakers are still on the to-do list. Gotta figure out which one is more appropriate in a given situation (from what I've gathered the driving factors involve the price difference and the response time) As for terminal blocks, I haven't gotten to that stage yet but that's also on the to-do list.

Lancie1 said:
Every electrical device should have a fuse or circuit breaker. In your case for your first project, yes you should add a 0.5 Amp 120 volt fuse inline on the supply end of the black "continuous common wire" shown in the American Stack Light diagram. This stack light is rated for 8 watts at 120 volts = 0.06 amps, but a short circuit with no fuse could pull 20 amps. If the 120 volt power to the stacklight comes from a separate circuit, and you run it back to relays in your control panel, then you will need to label your panel with a warning sticker that "This panel has more than one power supply", or similar, and list the location of all breakers to kill all the power.
Click to expand...

Thanks for the heads up on this. Does my current design qualify for having multiple supplies then? I didn't put a "master" breaker in this design, only a disconnect. For whatever reason, I was thinking my breaker layout would be appropriate, but you are making me think I still need some type of a master breaker or fuse.



Just to share, these are some of the larger more immediate items on my 'to-do' list of info I'm missing thats holding me back from the next step (the known unknowns):
  • Fuses and Breakers: sizing, type and placement. Mostly type and placement.
  • Hydraulic Solenoids: circuit protection?
  • Motor starter relay: make, model, protection accessories
  • Safety Relays: detailed wiring.



Phew, there it is. Thanks again everybody for your help. I'll keep updating with the progress. And I promise I'll keep it safe.
 

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