Real Time Sampling with PLC5-40E and 1771-IXHR

[cdroot4383 0]

Hello, I am currently using a PLC5/40E rev C and a 1771-IXHR rev J thermocouple input module in a 1771-1AB chassis. My question is that our application requires a temperature reading every 200ms. Under the I/O configuration i can adjust the RTS to the desired 200ms. We are linking this program to RSView for data collection. Under the data logging options (under periodic), we've set that value to 200ms as well. When the data is recorded and dumped into excel, the timing of the data is sporatic and ranges from 160-240ms. I wanted to use the on demand triggering, but I could not find a bit in the block transfer read that would indicate when the RTS took place. Is there a bit in the IXHR module that indicates when a RTS takes place? Is there a better technique to acquire the data in RSView to ensure the data is acquired at the 200ms rate? I've explored the possibility of OPC to dump the data in excel, but I have never used it. Any solutions or recommendations would be greatly appreciated. Thanks in advance, Chris Using RSLogix 5 Version 7.10.02 (CPR 7) RSLinx Classic Professional Version 7.10.02 (CPR 7) RSView32 Works 7.10.00 (CPR 6)

[Leadcommander 0]

If you are use the data for analysing purposes and only require a block of data with exact 200msec intervals, you could trend the data using the RSLogix5 Trends. Then export data to Excel. Sorry can't help with the RSView32 trend. Edited 22 Mar 2007 by Leadcommander

[Gerry 13]

You can be confident that the readings are taken at 200 msec intervals since that is controlled by hardware on the 1771-IXHR. The time-stamps in the RSView datalog only indicate when RSView actually logged the data which is subject to vagaries of the ethernet comms and windows OS. There is a possibility of missing a reading when RSView's interval extends to 240 msec since the relevant clocks will not be synchronised. An alternate approach would be to buffer a series of readings in the PLC and log them as a group. For example, 5 readings logged every second. You could dress it up when you transfer to Excel.

[cdroot4383 0]

thanks for everyone's help. It seems that it should be fairly simple to dump a couple of integer words from the plc into excel. We have the rstrends, but I figured that it had it's own sampling rate similiar to the "periodic" function and would also cause the samples to potentially range from 160-240 ms/sample. From my original post, is there an internal bit in the thermocouple module or plc that triggers when a RTS takes place? thanks, chris

[Gerry 13]

The DN bit of the block transfer read instruction should be on for a single scan after each update. Question: is the TC module local or remote? If remote, there are additional timing concerns.

[cdroot4383 0]

Gerry, you were right, I was watching the data table and didnt notice any changes, so i assumed that it wasnt working. after adding a ONS after the DN bit with a counter, it verified that the bit was changing properly. however, i am still having problems properly datalogging in RSView in trying to do the event trigger. Is RSView capable of recognizing a 200ms false to true transition consistently? the scan class is set to the maximum (0) and the event setups are at continuous. A simple latch using the EN and DN bits are used for the false to true transition. any suggestions are greatly appreciated. thanks in advance, chris