I need help interfacing PLCs with computers!!

[Abed Mqayyad]

Hello everybody,

I recently got a new job in a batching plant factory. Programming the PLC is part of my new job, I am good at ladder programming actually, however, they need me there to develop a way so that we don't have to use the "control panel" anymore. We want to make it all computerized. I think this is called "interfacing"?, I am not sure though. Unfortunately, I am very new to the world of interfacing. I have no idea how to send a signal from my PC to the PLC!!

In the past two weeks I have been looking that up in the internet and finally I came here. I found out that interfacing between PLC and the computer can be done by a VB code in a GUI environment. I am not that good at VB though. Also, I have read some articles in this forum about "win cc".

My questions are:

1) Where should I begin if I want to learn how to interface a PLC with a computer? Should I learn VB prg. language? Or should I just begin learning "win cc" and that would be enough (regardless of the PLC type) ?

2) In our work, we use devices such as "BONGSHIN Digital Weighing Indicator BS-7220", however, I was wondering how to show the value being indicated on my PC screen?? For example, if the indicator is displaying 100 KG on its screen, how could I transfer this number to the indicator inside my program? Moreover, this is not the only device we use, we also use counters and sometimes timers and I will need to read their data and show it on my PC screen.

3) The types of PLC I have seen where I work are two: 1) LS GLOVA G7F-AD2A from LG, 2) Zelio family from Schneider. Anyway, I can require another types if it is important, though. So, what port should I use to connect the PLC with the computer, Serial port, Parallel, or Ethernet? I really have no idea!.

Finally, I am sorry I might be a little bit confused but I think it is only because I am very new to interfacing or HMI. I need somebody to guide me and direct me to the right direction. Any help would be highly appreciated. Thank you all for your time and consideration.

(Sorry about the language, it is just that English is not my native language)

 

[Tom Jenkins]

You don't want or need to develop your own interface with visual basic. Research SCADA (Supervisory Control and Data Acquisition) software. All major PLC manufacturers have some version of SCADA software, plus there are third party packages like Intouch and Wnderware. These are specifically geared to do what you want to do, and include built in functions for trending, alarming, data logging, setpoint changes, etc. Best of all they handle the communications to and from the PLC without your having to write your own comm drivers.

 

[Abed Mqayyad]

You don't want or need to develop your own interface with visual basic. Research SCADA (Supervisory Control and Data Acquisition) software. All major PLC manufacturers have some version of SCADA software, plus there are third party packages like Intouch and Wnderware. These are specifically geared to do what you want to do, and include built in functions for trending, alarming, data logging, setpoint changes, etc. Best of all they handle the communications to and from the PLC without your having to write your own comm drivers.

Thats interesting, but I was wondering would it be enough if I learn "win cc" or is this program only for Siemens PLCs? It would be more clear if you name few PLC manufactures and the associated SCADA program. Thank you very much for your help

 

[Fred_Loveless]

WinCC is a Scada/HMI (Visualization and Control). You will still need to communicate to the devices to get the data back to the HMI. WinCC will have drivers/Servers that allow it to talk to Siemens hardware but you will need a communications server to talk to Non-Siemens devices.

 

[Lancie1]

Abed,

It is a difficult task to develop your own PC to PLC operator interface. Much better to use ones already developed. A large problem you will have is connecting different brands and models of PLCs to the same PC control computer. It helps if all your PLCs are connected to the same common communications network.

 

[parky]

They are right, it depends on the amount of data you will need,
I believe Beijers have a small PC Based scada 1,000 tags for about £1K this was called CEZAR
If you are going to roll your own then you would need an OPC Server like Kepware (KepserverEx), each protocol will cost about £500.00 these can have multiple protocols then you could use the opc foundation dll supplied in your VB there are some good examples with kepware.
I am currently doing this & I have found the best way is to use encapsulated Ethernet with Rs232/422/485 Ethernet server modules these are about £120.00 each then use the virtual driver that comes with them i.e. you create 1 to xx comms encapsulated into ethernet then use each one for each different plc.

 

[Abed Mqayyad]

but you will need a communications server to talk to Non-Siemens devices.

I am sorry I really don't have any idea about this "communications server" and how to work on it. However, I can tell my boss and he would require Siemens PLCs but I want to learn what is the communication server and how to handle it.

Lancie1 & parky:

All right, but actually I won't be using that much of data in my current project, all I am working on is only one PLC. So, I will not have to use Ethernet encapsulation, right? I am assuming that my PLC only has a serial connection. But taking a look back to it, I will be using more than 3 digital indicators for weighing and counters and I will need to read their data and display it on my PC screen (which only has on serial port)!! how can that be done?

 

[danw]

The RS-232 on the PC's serial COM port is for point-to-point communications only; meaning it can talk only to one device.

If the scales have RS-232, then you need to add serial ports to the PC and connect each scale to its own serial port. There are numerous multiple serial port add-ons for PCs.

It is not uncommon for the scale manufacturer to have an alternative serial port, an RS-485 port. RS-485 supports multi-drop, meaning multiple devices, one after another, wired in a 'daisy chain': PC to 1 to 2 to 3 to 4 etc.

Using RS-485 with multiple devices assumes that the scales can be addressed through some protocol (the language rules used over the RS-485) so that only one device talks at a time and it's clear who is talking and who the message is addressed to.

There are commercial RS-232 to 485 converters for the PC side.

 

[Abed Mqayyad]

^^
That was really helpful, thank you very much.

The scale I will be using is BS-7220 from BONGSHIN which consists of RS 232 and RS-422 so I basically don't have to add serial ports to the computer, do I?. The other thing going in my mind now is that probably I can read the scale data through the PLC since the scale is already connected to the PLC.

In our work, we have three to five gates which open to discharge materials sequentially. For example, I would set the first gate to discharge 100 Kilograms first, then its gate would close and the gate no. 2 would open to unload 300 KG, .. etc. After I obtaining the desired aggregate weight, a motor is supposed to run to move those materials and so on. Basically, I would assume that the PLC will not be having any kind of information about the reading of the scale since it only receives a "finish" signal from the scale! Its confusing!! Do you advice me to use an analog scale? and maybe somehow I can send its data directly to the computer?

 

[Tom Jenkins]

Abed, you need to do some self-instruction in fundamentals of SCADA. Wikipedia has a decent place to start:http://en.wikipedia.org/wiki/SCADA

There are a lot of SCADA related posts on this site as well.

As Dan says, if your RS-232 devices are addressable (most are) and share a common protocol then you can use RS-232 to RS485 adapters to daisy chain them on a network. You generally don't want to mix protocols on one link, as some interesting things could result. I suspect most of your devices and your PLCs (certainly the Schneider) can talk Modbus, the most common protocol.

A communciations server (or driver) is simply programming that constructs a communication packet to get the right data to and from the right device. The packet usually consists of several portions like header, command, device address, register address, data, and error checking. The differences between the location and constructions of these parts of a data packet is what constitutes a protocol.

To me the amount of information you need is not going to come from an online forum like this. I suggest you get some books or work the web and get grounded in the fundamentals. Your local automation vendors may also be able to help you with info. Then come back with more specific questions.

 

[Abed Mqayyad]

Yes you are right and that is why I said I am very new to SCADA and HMI. I have been looking in the internet and found many useful articles and honestly, I gathered the most useful information from this topic. I basically constituted an idea about HMI and SCADA and my next step.

Thank you all for your help and kindness.

 

[presys]

Try looking on to InTouch SCADA, which is probably the most widely used SCADA software. InTouch has a wide variety of DA (Data Access) servers which you could use to connect with the devices you mentioned in your post. Other communication methods are also available, such as OPC servers.

http://www.scadadev.com

 

[parky]

If you read my reply fully you will see that using ethernet encapsulation is a way of communicating to many plc's even those using 232, using Ethernet to serial converters, this is a clean way of doing it as you probably have an ethernet port on your pc plus many companies have a factory network & a lo cost switch with 8 ports could be located close to the plant & the pc in another office so you don't have to worry about the distance that you would on 232 but you do need the hard ware, however black box do a number of multiple port 232 cards so you could use one of these if the pc is going to be close to the plant.

 

[Panasys]

A interface for Zelio using serial conection

Is an application that work on Xp and Seven.

www.z-scada.com

Is very easy and quick setup.

No need ethernet module expansion.

Resgard

Javier

 

[md.abdullah]

Wincc is tough rathere than intouch.intouch has very easy to understan and start from new scada learning.it has also very wide of supporting the communication server and easy communication methods to communicat from plc to your intouch scada.
for the Seimens you can use PPI and MPI protocal to communicate to your pc....try as all said from the Intouch..
best of luck..