Hello People,

Is there any place which tells us the maximum number of ascii characters that a PLC could read in a single scan or maybe 2 or 3 scans. The requirement is that we need to read RS232 data from a weighing balance (Sartorious) whose character length is approx 500. I am assuming that the maximum that Siemens's PLC's can read is 255 (please correct me if I am wrong). But if its something like 500 chars which needs to be read, expanding the character array is the first step, but would it allow to read that many number of characters?

Kindly advise. Would like to hear your opinion on the same please.

Grim Reaper

Hello, you can check that on online help on step 7.

Regards.

Hello.

Are you perhaps using or think of a STRING? A STRING as buffer will limit you. An array of CHAR will give you the best option.

~

Rescobedo

Hello, you can check that on online help on step 7.

Regards.

 So Are you trying to say that we can read more than 1000 ASCII characters? I've posted 2 pictures here with the message. They are from weigh scales. It has an internal RS232 port and the data that comes out is ASCII for the record. WE were able to read it with hyperterminal. Point I am trying to make is that the number of characters would extend beyond 253 in most of the instruments. How are we to capture the data from them. Please refer the attached pictures on how the data is being requested by the customer. This is the daily and monthly calibration reports from the weigh scale.

qwazee

Hello.

Are you perhaps using or think of a STRING? A STRING as buffer will limit you. An array of CHAR will give you the best option.

~

 Hi,

That is the next step. I was worried about the limit that I would be seeing. I am in a situation where I may have to read between 77 and sometimes up to 1500 chars. The array of characters is the first option. We can convert / concatenate them to a string after decoding the ASCII to normal characters.

But I need to know if I used am S7-1200 how many chars in a single scan would I be able to read.

Say that I used the CB1241 (I hope that I got the communication board number right). I have multiple instruments with RS232 ports on them. And there is no friggin way I would be able to multidrop them to a single serial port. So I need to purchase hardware for the same. Now I assumed that the number of characters from a weigh scale or a pH instrument or a conductivity meter would  at the most be a single line (my bad).

It is a whopping 80+  number of characters that I am look at now. Some cases have characters up to 500+. In the previous post of mine I had posted a slip showing daily calibration report of a particular weigh balance. Now there is a monthly report of the same. I am posting it here as an attachment. FYI please refer to both the pictures that I had posted. I was unable to post both the pictures in a single shot.

Grim Reaper

But I need to know if I used am S7-1200 how many chars in a single scan would I be able to read.  

What is preventing you to confirm by lab test that the specification given by Rescobedo is correct?

Just note that the read in "one scan" is not true. The serial communication card records the data until it has the full package. The instruction in the program then takes from this buffer.

The code instruction will give a 'done' signal when it is finished. The activation of the instruction can be more than one scan cycle.. it is an asynchronise function. Interrupting the execution of the instruction will cause strange behaviour.

I am expecting there is a start and end character to tell the PLC when the data package is fully received. This is configured in the hardware configuration of the serial communication card.

Please keep these hints in mind and read the documentation on the serial communication instructions again.

Good luck.

Hello, maybe its cheaper for you to buy Nport5210 devices.

I work with some equipment that has multiple code scanners and since the plant wants the scanner with only RS232 Com, due to the easy plug and play replacement, we came up using Nport5210. This gateway can handle 2 RS-232 devices and send the data through TCP/IP sockets.

So, we plug 2 scanners to one Nport device and from Nport to PLC though TCP/IP Socket using the integrated Profinet ports on PLC CPU, and as far as I know, this Nport device is cheap.

I hope this suggestion help you. 

MOXA Nport 5210.

Regards.