Very easy question from a beginner!!

Hello everyone,

I am very new to PLCs and I have a Siemens Simatic S7-200 for my project. I have a tank in which a process occurs. This tank becomes hot after some time and in order to control its temperature I use a temperature detector. This detector sends the temperature data to the PC and the PC records the values. Then I have to read these temperature values from the computer and when it gets above a certain value, I have to run a program on the PC which sends data from the serial/parallel port of the PC to the PLC in order to operate a pump that pumps the chilling water to the system for cooling it down. The problem occurs here!

How can I send the "temperature is high" signal from the computer to the PLC ? (I mean the connections, the hardware thing?) And how can I operate the pump when the PLC gets the "temperature is high" signal from the computer? (I again mean the connections.) How should I connect the pump (220 V) to the PLC output? And how can I connect the computer to the PLC input for sending "temperature is high" signal??

I would be very glad if you could help me in this desperate situation.
Thanks very much for your time.

Emrah

Hello Emrah!

Let's see if this would help.
In the software part: connect temperature input value to a comparator which compares this to a specified "high level setting". Use greater than or equal to function then connect it to a digital output. Choose an address for DO, (hardware part) from this you can determine which DO module terminal you should connect the wire to the pump's start command input. As far as I know, S7-200 has a built in 4 DO.

All signal communications with your PC will be through your RS232 (serial port) or MPI cable. When connection between PC and PLC is established, you can force values from the PC.

Zarah

I need more descriptions

Hello Zarah,

Thanks for the reply. But, I think I need more descriptions. Maybe I need some very simple schematics. I know that I have to reserve a DO for sending output signal from the PLC to the Pump. But I am not sure if I have to use a motor starter (actuator). And I also do not know how to connect the cables (which cable to where) on the PLC. Ok! I will get the data (I think from a single pin of RS-232) from the PC to the PLC. And as the dedicated input port of my PLC becomes high, it will generate a digital output DO. But how will I connect the cable of the pump to the PLC?..I am terribly afraid since it is high voltage (220 V)...

Please more help...
Thanks again.
Emrah

Your going to have to use a relay. Connect your 220 to a set of normally open contacts on your relay. You can use a solid state relay or a contact relay. Although, in my experience, solid state seems to be more reliable. Then connect the output of the plc to one side of the relay coil, and the common to the other side.

Yes, he's right. You are not going to connect your digital output directly to the pump. Connect wire from DO terminals to a relay. The relay is then connected to the pump.

Hope this helps.
Zarah

"I am terribly afraid since it is high voltage (220 V)..."

I'm a little afraid for you as well. The question you have asked about hooking up the motor makes me think that you are maybe a little over your head electrically. Is the motor single phase or 3 phase? What is the horsepower (or kw) rating? Do you have branch circuit protection, overload protection etc...?

You can play around with your PC and PLC all day and not get hurt and I encourage you to do so as it will be very educating. However, get a hold of someone (an electrician) before you hurt yourself or your motor/pump. If you give me the specs on your motor I can help you out but I still encourage you to seek local help.

allscott, Your very diplomatic.

However, I would suggest that the origional poster totally stop all work and get in somebody qualified to assit. Unless he's in Anartica, and its a matter of life or death, he should have another qualified person on site to provide assistance.

"allscott, Your very diplomatic."

I am fairly new to this site and am trying to be as diplomatic as possible. I know I've already po'd a couple of people and I just might need help from these same people one day.

It is my opinion that if anyone is "scared" of electricity they should stay away from it or obtain proper training.

I work with voltages up to 230KV on a regular basis and I am never scared. If I feel scared I know that there is something wrong with what I am doing and stop. Respect yes, scared no. With proper training, understanding, and procedures electricity can be worked with safely. If your scared of the equipment you are working with then something is wrong.

I was a bit dissapointed with some of the previsous posters telling this guy to hook his motor up to a Relay. He obvisously has now idea of what he is doing. For all we know this is a 300HP motor he is trying to control and we are telling him to hook it up to a relay?

BTW, how do you guys quote a previous post in the box with the black outline? I've looked around and can't quite find how to do it.

Motor Control

I agree with you allscott. If the user doesn't have much experience I would recommend to have someone with more experience to assist him. Like you, I also respect electricity.

Although, what he is trying to do is fairly simple. He simply wants to Turn ON and OFF a Motor from a PLC. All we know about this motor is that it works on 220VAC. I am not sure where that 300HP came from? Maybe I didn't read everything. I would say that having all the information on the nameplate of the motor would be a good starting point.

The PLC is only going to control a bit. Obviously, he will need either a Contactor or perhaps a Drive to control this Motor. A relay might be fine also but again we don't know anything about this motor.

If you look along the bottom of each reply over on the right is a "quote" button. This will generate a Reply w/quote. You can also type
["quote"] to start and

["/quote"] to finish.

Do not use the quotation marks. I had to use them to prevent generating a quote box. lol

Bob

TO THIS DAY I AM SCARED OF ELECTRICITY, just got use to working with it. The stuff likes me to much tho, I am like a magnet that attracts it, I dont even have to touch things at times for the power to arc to me....SCARY. Thing is I can see the stuff, not physically per se but I dont have problems following its path(s). I understand how it is created, how it works with devices, the force(s) created, the use of it and the DANGER of it. I reckon the only thing I have ever respected or been scared of more was my Father.

When I first saw this question I started creating a pictoral guide to connecting a single phase and a 3 phase motor to power and a plc digital output. I seem to have alot of free time and it would go well on my site but I decided I shouldnt. I will create the pictoral guide for connecting something like this over the weekend but I think the "poster" needs to do a lot more studying before any answer could be understood.

As for the pictoral guides I think I will expand it even further and go for connecting inputs, AC and DC, sinking and sourcing. I will work on analog and high speed counter connection examples too if possible. Got any ideas on what other connections I could show?

Allscott,

You are right. Perhaps I was a bit too hasty when telling this person to hook a relay up. Assumption is the mother of all mistakes, and I assumed this person knows more about what he's doing that he probably does. Immediately after posting that info, I regretted it. He should indeed seek out someone who is qualified to do the motor install.

I'm new here too and trying not to P.O. too many people either



As for electricity, I am still afraid of it, that's what makes me respect it.

Ron,

As I'm not so much afraid of the juce as I am of myself, I frequently refer to my little NEMA pocket guide, and YOUR site, when I cant find the guide burried under the pile on my desk. (the keyboard and monator always seem to show through the mess). 6, 12, & 9 lead motor connects, and standard wire labeling would be great, if ther not already there. Sink/sourcing info would aslo be great.

You have a great reference site. Thanks a million!

Mike.

I have how to wire together 6, 9 and 12 3Phase motor lead connections and single phase:

http://www.patchn.com/motor_connections.htm

I have Terry's explanation on sinking and sourcing:
http://www.patchn.com/npnpnp.htm

The wire labeling I will work on.