PLC Controlled greenhouse

[DWF]

I would take a good look around this site:

http://www.automationdirect.com/

Particularly, take a look at the DL06 PLC line since you will probably want a Real Time Clock. I belive the CLICK line of PLCs have a RTC on some models as well.

I have many, many AD products in use in my facility. You cannot beat their price and I have found their products to be just as reliable as any other vendor.

I haven't bought from these guys, but their pricing looks very nice:

http://www.factorymation.com/


I would not buy from Grainger unless you are interested in paying 3X the price for the same thing you can buy elsewhere.

 

[Clay B.]

Something you will need to define.

On your inputs you have listed a lot of specialized sensors. The method they attach to the PLC is going to have a big effect on the type of PLC you purchase.

My point is what type of OUTPUT do these sensors make. Is it serial, 0-10 vdc, 4-20 mA, ethernet...etc

Alot of the 'smart" relay style PLC's are limited in this area 2 ways. The first way is the comunication itself. Your PLC will need to be compadable with the sensor. The second is memory. Analog type sensors use alot more memory than discrete and this has to be considered when sizing a PLC.

As several have pointed to "how to deal with things going wrong" you are going to find that what you have listed is not going to be enough.

Example: Pump that runs all the time kicks out. How will you indicate this? Will you use a light, an HMI, an email to your computer...

When selecting the PLC how the operator (in this case you) interacts with the system has to be taken into account.

Sounds like a fun project. Good luck

 

[JBJennings]

I would go to the extra expense of using a 3 position switch for all my outputs. This accomplishes several things, the least of which is being able to completely power off the output. You can also control the output in automatic mode (PLC) and manual mode (on all the time). We refer to them as HOA switches (Hand-OFF-Auto).

 

[OkiePC]

Something you will need to define.

On your inputs you have listed a lot of specialized sensors. The method they attach to the PLC is going to have a big effect on the type of PLC you purchase.

My point is what type of OUTPUT do these sensors make. Is it serial, 0-10 vdc, 4-20 mA, ethernet...

This is an important consideration. Thermocouples are cheap and reliable, but a PLC input card for millivolts/thermocouples might be more than twice the cost of a 4-20ma input card.

I would lean toward a standard voltage and/or current PLC input card and spend a little extra on signal conditioners for existing transmitters, or buy new ones with the correct signal outputs available to match the PLC card.

 

[Clay B.]

This is an important consideration. Thermocouples are cheap and reliable, but a PLC input card for millivolts/thermocouples might be more than twice the cost of a 4-20ma input card.

I would lean toward a standard voltage and/or current PLC input card and spend a little extra on signal conditioners for existing transmitters, or buy new ones with the correct signal outputs available to match the PLC card.

My main point here is in alot of cases you can "buy" you way out of a corner by getting a new card for your PLC but this is only possible if you are in the right platform to begin with. With the list you already have I would shy away from the "smart" relay level of controllers. I would start with a "Micro" level PLC ( S7-200, Microloigc, DL6... etc). I doubt you would ever get to the complexity that would require going above these. Infact going off your list and making a few asumptions, I would go with a Unitronics Vision 280.

Reasons:

1) Handle various analog I/O.
2) Built in HMI so no need for lots of switches and lights
3) The Vision 280 has a keypad. I assume in Organic farming you have some pretty grubby hands so I opted for a keypad over a touchscreen.
4) Remote I/O can get the Input and output cards where I neeed them
5) Setup cost, since this is your first, buying expensive software not cost effective. Assuming this is for 1 Greenhouse not 50 Greenhouses.
6)Cost per I/O is pretty close to being the cheapest around.

Web page for PLC: http://www.unitronics.com/Series.aspx?page=vision280

 

[Lancie1]

I’m going to take Bob A’s advise and take baby steps, starting with enclosures. I will be using a type 4 (thanks godfrey) but I’m not sure what size. I want to make this system safe so I want to make sure I get the right “boxes”. The system will be split in to 3 locations, inside the grow environment (~ 5 relays), one located in a utility room (12-15 relays) with a window?, and the PLC enclosure will be in a 3rd room.

For 3 separate enclosures as you described, I might look at using the same size NEMA Type 4 electrical box for each, probably about 20" high x 16" wide x 8" deep. Now, you could get by with a smaller box for the Grow area and the PLC, but for 15 plug-in ice-cube type relays, you will need most of the 20 x 16. Generally, the larger the box, the easier it is to wire it up and to do maintenance and troubleshooting. But the larger the box, the more it costs and the more space it takes, so it is always a trade-off. Also, the PLC box will need to be deep enough to allow door to close without hitting top of PLC (that usually means about an 8" deep box), but the other two boxes could probably be only 6" deep (whatever it takes to clear the tops of your plug-in relays). Also, only the boxes in wet areas need to be NEMA Type 4 or 12. The ones in dry areas (no hose-down) can be NEMA Type 1 General Purpose enclosures (much cheaper, no gaskets).

PS: Remember that the Mounting Plate that fits into the electrical enclosure will take about 1/2" out of the box depth, and for some brands, the door takes additional depth. All parts must be designed, selected, purchased, and built to work together - that is why they pay us the big bucks for this stuff!

 

[northpad]

Am I close??

So I started pricing some things out for my PLC, here is a list of equipment. I KNOW some things are not right for the system, but I would like to see if I am on the right track. Don't be too mean to me, I am new at this.... HAHA

 

[Paul B]

I'll throw up an opposing view to the 2-position selector switches for each plc output. These are the ones that have been suggested to allow you to control an output directly in case the plc fails.

When's the last time a plc failed? In industry we never do this. PLC's run for decades. Why put the effort into the selector switches? I sure would not do this.

For those suggesting this, would you do this on a machine in an industrial plant, as part of your typical design? You'd put a 2-position switch on the door for every plc output? This has been done, it was common years ago when plc's were newfangled devices, but nowadays, not at all. In my experience.

Maybe I am missing something.

 

[Lancie1]

Paul,

"PLCs" don't fail often - that is not my concern. New guy, new program, many possible ways to short out the PLC outputs, or to get the program so balled up that it won't run, which does happen ALL THE TIME. This is NOT an industrial plant. If it were MY greenhouse, I most certainly would put a bypass switch on the critical outputs. Like I said before, I would build this system first without the PLC even in the picture, using ON/OFF toggle switches, then once everthing is working, add the PLC cabinet and parallel the relays (controlled by PLC outputs) with the ON/OFF bypass switches.

There is nothing more frustrating that having the pumps and fans available to keep some plants alive, but no way to get power to them because someone left out some little ole cheap-a*s 120 volt toggle switches!

Northpad,

You probably will not need more than about 3 of the 1-meter long DIN rails. You might save about $30 by buying them someplace that will sell in less than 10-package lots. (There I have saved you enough to pay for about 10 of the bypass toggle switches - Allied Electronics Stock #683-0049 @ $3.10 each, that Paul is so worried about!)

In addition to the F2-08AD-1 Automation Direct Analog Input module, you will most likely need a Digitial Input Module for inputs from all types of on/off switches (as opposed to analog inputs from variable-signal devices).

 

[DWF]

Looking at your materials list... I would look at the DL06 line of PLCs rather than the 205. The 06 should be able to handle whatever you want to do.

 

[JBJennings]

The DL-06 is $275 cheaper with 8CH analog in and ECOM than the same 205 system. I would purchase the LCD option for the DL-06 with that savings.

 

[northpad]

Will this work?

D0-06DD2-D DL06 20 DC IN/16 DC OUT SRC MICRO PLC W/DC P/S

199.00 F0-08ADH-1 8 CH ANALOG INPUT 0-20MA 16 BIT DL05/06 OPTION MODULE

129.00 H0-ECOM 10BASE-T ETHERNET 05/06 NETWORK MODULE

175.00 D0-16TD2 16PT 12-24VDC SOURCE OUTPUT

58.00

 

[milldrone]

northpad,

I would add the ZL-RRL16-24
ZIPLINK 16-RELAY OUTPUT MODULE, 24VDC COIL, LED INDICATION
This unit has 10 amp contacts (sorry no 240 Volt) and plugs into the DC output module you listed before.
http://www.automationdirect.com/adc...ick_PLC)/ZipLink_Wiring_Solutions/ZL-RRL16-24

and the ZL-D0-CBL24-2P
ZIPLINK CABLE, 24-PIN TO PIGTAIL, 2M (6.6FT), DL05/06 PLC This is the cable to go in between the DC output module and the relay output board
http://www.automationdirect.com/adc...onnector_Cables_(Complete_List)/ZL-D0-CBL24-1

 

[Lancie1]

Northpad,

You still have no Discrete Input Module. I know you did not have any digital on/off type Inputs on your original list, but your list may be lacking. Here are some things you will probably need to turn on/off. How do you plan to do these functions using the PLC and modules that you have listed?

1. Master System On/Off Switch (or do you plan to kill power to the PLC each time you need to do a system shut-down?) Typically PLCs are powered up 24/7, and control inputs are done with input modules.

2. Day/Night, Summer/Winter, Daylight Savings/Not Daylight Savings switches for the three 240 volt timed lighting circuits.

3. Other Customizing Switches for growing certain plants. Maybe you grow some water-loving crops one season, then some other type that do not need as much water. Will you change your PLC program each time, or select the type of plants from input switches such as thumb-wheel switches? Perhaps one week it is mostly cloudy overcast weather and you need more artificial light and less water. The next week is bright sun and you need less artificial light, but more water and ventilation. How will you change your PLC program parameters to match the changing conditions - by constantly fiddling with the program, or with input switches for the various conditions, or by using an operator interface graphical control panel (which will allow programmable switches)?

4. The DL-06 model used to have off-line programming only, and I have not used one is several years now, but I bet it is still that way. So any and all program changes will require you to power down your greenhouse equipment (unless you have manual bypass switches!) while you load a new program or edit the existing program. For that reason you may want to minimize program changes and instead have external inputs that modify the program, which is a common method to change functions on-the-fly without having to do a PLC program edit.

These are just some things to think about before you get too far along with equipment selection.

 

[Lancie1]

Diagrams that I Promised in PM

Northpad,

Here are the block diagrams that I promised you. I think this is an important first step, before trying to make schematic and connection drawings. If you design the Relay Cabinet as I outlined here, you can operate your greenhouse without a PLC, then you may add the PLC cabinet later and you will be able to troubleshoot it separately while still operating the greenhouse.

This file is saved as a Microsoft Excel Spreadsheet, Version 5.0 (Windows 95) so that it can be viewed by many. I laid out and sized the 6 sheets to print on 8.5" x 11" paper so that no drawing plotting paper will be needed to get good prints.

Questions?