PLC Temperature Reading and Recording

Start with the tutorial here. Just click the 'Online Tutorial' icon at the top of the page.

Quite an ambitious endeavor on your part. However, this is just the kind of thing that gets a lot of people involved in PLCs.

Kinda like, wanting to build furniture. You buy all of the wonderful tools and some fine wood and then stare it - wondering how to use the tools to change the wood into furniture.

You'll certainly need to learn the basics. As Steve said, start by reading the Tutorial on this site - then buy Phil's book. It will be a worthwhile investment.

In general, you are looking at monitoring a number of Analog Inputs and then recording the values... somehow, somewhere.

You will need to understand how to install and connect the Analog Input circuit. Some PLC's have Analog Input capabilities built-in. There might be 2 or 3 of these Inputs available in the base unit. Additional analog inputs would have to be handled by additional Analog Input Modules.

Then you will need to understand how to "set up" the Analog Input at the PLC. You will also need to understand how to interpret the Analog Input value into a meaningful number (scaling the raw-number value into some Engineering Unit value).

At that point, you will have a "value" sitting in some V_Mem location. Then you'll need to figure out what you want to do with that value.

Are you going to simply display it on a screen?
Are you going to enter it into a log with a time-stamp?
How often do you want to "peek" at the temperature?

The number of "peeks" will affect the size of the log unless you find a way to dump the info to a file or printer immediately. Dumping to a file or printer is a whole ball-game in itself. You might or might not be able to do it at all! It depends on the capabilities of the PLC and the software you are using. You'll need to do a bit of research on this to be sure you can obtain what you need.

You're coming at this in a sorta backwards fashion, but then that's the way a lot of programmers develop their experience...
"Necessity is the Mother of Invention".

Good Luck and keep coming back with questions - but read the books first so you can figure out what questions to ask!

Thanks for all the tips and ideas, I'll definitally check out the online tutorials and stuff. Normally I don't do anything like this but the computer man my dad has just quit because he couldn't handle it and now if I quit then my dad will think poorly so, by the way I'm only 15. So its tough being thrown all of this when a few days ago I didn't even know what a PLC was. THANKS FOR THE HELP!!

VJN,

Hang in there; you can do it. I first studied computers when I was age 16. You may be short on knowledge and experience, but I know you can make up for that with your enthusiasm and energy! Things will start to make sense after awhile.

You stated that your Dad "...purchased an Automation Direct DL05/06 PLC". Just checking the Automation Direct catalog, I see that they have a DL/05 or a DL/06 processor. Because you are measuring temperatures, you will need some analog input modules, so I hope that you actually have a DL/06 PLC chassis with 4 auxiliary "slots" that can be used to plug in additional Analog Input cards. (The DL/05 processor only has 1 "option slot" available.) Then you will need some catalog #F0-04AD-1 Analog "Option Modules". Each of these has 4 analog inputs, which can be used for 4 separate temperature inputs (from a 4-20 miliampere Temperature Current Transmitter). Each transmitter will need to have some type of temperature sensor (thermocouple or Resistance Temperature Detector) wired to it. The sensors are what measures the temperature and sends the signal to a transmitter, which in turn, sends it to the PLC Input Module ("option card". When you get all your hardware worked out, come back here and we will tell you more!

Personally VJN, finding this site was a major step

You may be only 15 but to be capable of locating the ONE site that can actually teach you what needs to be done...that says alot.

I believe you have what it takes, otherwise you wouldnt be here. Take a shot at this and see what you can do.

Note: DirectSoft32 offers some example programs to view/edit etc.
The DL05 is a small but very versatile unit that is simple to program and learn to use. Read the manual, instruction set (the things used when programming), read the tutorial here.

If you need to understand a little more about control wiring, hydraulics/pneumatics, how-to's in general then you may want to visit:
http://www.patchn.com

I may be able to offer information that will allow you to easily surpass me in a short period. I am willing to assist in any way I can so feel free to post any questions here or at the above. I am also available via email etc anytime.

... no, I don't have any kids - but ...

... if I quit then my dad will think poorly ...

Click to expand...

Personally, I’m glad to know that there’s still a 15 year old kid out there (somewhere - anywhere) who actually gives a darn about what his father thinks.

VJN,

We ALL want to see you succeed with this project. Why don’t you help us out with a little bit more information about exactly what you’re trying to accomplish?

Why do you need to measure the temperature of a “concrete plank”? What are the minimum and maximum temperatures of these planks? For how long a period (minutes - hours - days) does the temperature need to be measured? How fast (degrees per minute - or degrees per hour) does the temperature change? How many temperature inputs do you actually need to measure at any one time? How will the sensors be mounted to the planks - (imbedded in the concrete - strapped into place - etc.)? How far away from the planks’ positions will the PLC be mounted? Will the planks move while the temperature is being measured - or will they just sit there in one place? Will the PLC actually need to CONTROL anything (turn something off or on, etc.) or will it simply pick up the temperature readings? What happens to the temperature readings once they are picked up? Will the PLC need to store them temporarily in its own memory - or will the temperature data be moved into a separate computer’s memory for storage - or will the temperature data simply be temporarily displayed on an operator’s screen as it comes in from the field? How much money do you have in your budget? What type of deadline are you working against? Anything else that you can think of that we really ought to know about?

Suggestion: Copy-and-paste the list of questions above into a Word document - then space out the questions and answer them one-by-one. Then copy-and-paste the Word document into a “reply” window on this forum.

Sorry that I personally can’t be of much help with the DL-type PLC - but there are a lot of highly capable people who hang out on this forum who can. The more they know about what you’re trying to get done, the more time and money they can save you - and the better the final results are likely to be.

Also, always try to be as specific as you can when you talk about the hardware and the software that you’re using. Different models and versions often require different answers. Give the actual model numbers, etc. whenever it’s possible.

Survival tip department: Even if you’ll eventually need to monitor (... let’s say ...) 16 temperature sensors all at the same time, it might be a good idea to experiment by monitoring (... let’s say ...) just one or two sensors to begin with. Then once you’ve got the techniques and the hardware all working correctly, expand the system along the same established lines. It’s very embarrassing to spend the entire budget on something that “should have” worked - only to find out that you really needed something else instead.

And - a word of caution - but please do NOT let this discourage you in any way. You need to understand that the project that you are attempting to do is not a typical “beginner-level” project. The tutorials and literature that you’re likely to pick up are usually geared toward learning PLC’s from the “ground up” by first controlling simple “on-and-off” circuits - things like opening and closing garage doors - and sequencing traffic lights. On the other hand, your very first project is going to involve “analog signals” and quite possibly “data collection and storage”. The techniques required to handle these types of tasks are more complicated - and so most beginners work their way up to them over a period of time. Depending on how tight a deadline you’re working towards, you’re going to have to move (more-or-less) quickly beyond those simpler “on-and-off” ideas and on into the more complicated “analog signal” world. This CAN be done - but you’re likely to need QUITE a lot of help to make the jump successfully. Luckily you’ve found a very good source of help - the people on this forum. The most important point that I’m trying to make here is that you shouldn’t blow all of the (limited?) time you have available by trying to master the “traffic light 101” course. Keep your eye on your ultimate goal and use your “learning curve” time as wisely as possible. You can always come back and work on the traffic lights later. (Note: This particular advice might suddenly change if (for example) you tell us that your PLC will actually be required to control certain things after it collects that temperature data.)

Finally, keep careful notes on everything you’re doing. This would be quite an impressive project to mention on a future job interview if you decide that you actually like this type of work.

Good luck - and welcome aboard -

Response Leter w/ Details

Below is a letter written by my boss and it should give all the missing details about this job. I hope its helpful.


"We are planning on reading a product temperature, recording it, and then plotting a time/temperature curve. As well as activating or shutting down a furnace according to the curve. This is to be done on six different products and furnaces.

Our intention is to use a PLC with thermocouple sensors, which we have bought and installed in our network. The system is connected to a PC on which we have the software instelled.

The source that we purchased from is "automationdirect.com" and bought a DO-06DR PLC, and the software that supports it.

We have done the wiring for the thermocouples , the connection to the pc, and the signal to the furnace will be done later."


Ron here are the answers to the questions you asked:

Why do you need to measure the temperature of a "concrete plank"?

We need to measure the temperature of the concrete as the chemical reaction of the water and cement is accelerated by introducing heat.


What are the minimum and maximum temperatures of these planks?

The minimum temp is 32 degrees F and the maximum is 180 degrees F.


For how long a period (minutes - hours - days) does the temperature need to be measured?

Measuring periods vary from 4-72 hours.


How fast (degrees per minute - or degrees per hour) does the temperature change?

The optimum temp change is (15 degrees F/per hour.


How many temperature inputs do you actually need to measure at any one time?

At one time up to 6 inputs could need to be measured.


How will the sensors be mounted to the planks - (imbedded in the concrete - strapped into place - etc.)? How far away from the planks' positions will the PLC be mounted? Will the planks move while the temperature is being measured - or will they just sit there in one place?


The sensors are thermocouples wires, twisted together at the end and burried in the concrete within a small tube. The concrete will be stationary.

Hi VJN, Sounds like you are getting into what should be a fun Project...the company that I work for makes concrete blocks, and we use a similar setup to measure the effects of different additives on the cure time/temps of our blocks, both for R&D, and QC. I will be happy to help field your questions, and, I hope, your success in this project. I echo Rons' statement that we all are more than happy to see a young person diving in to this Art... and hope you learn to love it as much as we do.
beerchug <<<ROOT BEER<<<<
David

VJN,

As RSDORAN said before, some good example programs are included with the DirectSoft programming package. From the DirectSOft main menu, go to File, Open Project, and then navigate to the "Projects" directory, then to "Samples". I remember that there is one under the DL06 menu that deals with Analog Inputs. That is what you will need to be able to set up. If you see no sample programs, then probably they were not installed by whomever loaded the software program originally. You can reinstall and choose to load the Sample programs.

You will want to set up 6 ladder rungs, one for each of the 6 temperature inputs that your boss mentioned. For each temperature input, you just "scale" the number that is being sent to memory by your analog input. By "scaling" we mean that you take a number that is in one range and convert it to another range. You will want to scale the input (representing a current signal in the range of 4 miliamps to 20 miliamps) to a temperature that matches the range of your thermocouples. Assuming Type J thermocouples (ask the boss if they are Type J), that would be about -346 to 1400 degrees F.

You will need to learn how to set up scaling for Analog Inputs. Below is a link to the Automation Direct Analog Input Manual. You may download it for free, or browse it online.

http://web1.automationdirect.com/static/manuals/d0optionsm/ch3.pdf


The general equation is: Y= mX + b (does that look familiar from your math classes?). m is the Slope, b is the Offset.

For your PLC temperature input, it translates to:
Scaled Value (output) = Slope X Input Value + Offset
Slope (m) = (Scaled Max-Scaled Min)/(Input Max-Input Min)
Offset (b) = Scaled Min - Slope x Input Min)

Some PLC's such as the Allen-Bradley SLC, have a built-in function to do Scaling. Yours doesn't, but no big deal. Just use some math functions. Your DirectSoft Analog Input Module has a Maximum output of 4095 and a Minimum of 0. So your scaling equations become:

Slope = 1400-(-356) divided by (4095-0)= 1756/4095 = 0.4288
Offset = -356 - ( 0.4288 x 0) = -356
Scaled Value (Temperature) = 0.4288 x Input Value -356

Now, all you have to do in each of your 6 rungs is, take the input from the analog input module, multiply it by 0.4288, then subtract 356.

So on each Temperature Input rung, you would do:

LD (load) Vxxx, (where the x's mean a Variable Memory location where you have the analog temperature input. You get to pick where you want it by when you set up the Analog Input Module.)

MUL by 0.4288

SUB 356

OUT Vxxx, where xxx is a V-memory location to record the temperature in degrees F.

I hope this helps! If it sounds like too much, read the above mentioned manual.