SCADA Data collection assistance

I am trying to get an answer for this question but sales guys dont always have all the details. So I am hoping by posting it here someone can answer it and give a snippet or the required code to make this happen.

I am sure that it will probably be required to write VB code no matter which SCADA software package one chooses to do this task so I am asking this as a general question.

Lets say I am monitoring a boolean bit in the PLC. When this bit goes active I want to do the following steps:

1. Poll the PLC and get the most current values for the registers I am using for the data collection.

2. Once this data has been updated write the information to our SQL server.

The scan time, by using KepServerEX diagnostics is running at about .5 seconds. The scan time in the PLC is 26mS. The protocol is Modbus. The data in the registers should remain there and unchanged for approx 4 seconds. All I really want to do is make sure the data is updated before I write it to SQL.

The two software packages that I have tested thus far as soon as the bit goes active it writes the data and some of the written data is inaccurate because it has not been updated.

Any help here greatly appreciated.

You should be able to do this without any trouble. Can you put the data into a buffer in the PLC then just read the buffer. That way you will get just the snap shot of the data at a high rate. Then the SCADA system has more time to read the data without it changing.

I do this type of thing with Siemens WinCC Flexible. I read around 25 DINT's every 20ms into an array 500 long. I then upload the array to WinCC Flexible. I read this on every cycle of the machine. I also have 4 more arrays so I can keep some history. Everytime I start another cycle I move the data accross the other arrays so I can pull up the last 4 cycles. This is a great trouble shooting tool.