View Full Version : ab plc5/20e update time
June 3rd, 2002, 02:15 AM
Need help. I am tring to create a graph. time verses an analog input from a pressure transducer. I need to look at a 20millisec window recieving an update every 1millisec. I also need to display this graph on a 1400e panelveiw I am using rslogix. thanks in advance
June 3rd, 2002, 06:55 AM
You may be asking for more than your hardware can deliver. The 1771 analog input modules don't refresh their data as fast as you need, and your PLC scan will likely be an order of magnitude slower.
Depending on the model number, a 1771 analog input module updates it's data from 5 mS/8 channels (1771-IFF)to as much as 500 mS (1771-IL).
Even assuming that you could get fresh data that frequently in the CPU, you won't get it transferred to the Panelview that fast, so if your intent is to make the PV behave like an oscilloscope, you'll be disappointed.
If you still want to proceed, your strategy should be to store the value from the analog channel at the fastest practical rate in a sequence of N-registers using a FIFO or Shift Register type of instruction. Then work out a ladder logic sequence to unload the values from the stack into a destination register that the PV monitors. Use the trend object in the PV to display the data. I'm not an expert in the use of the PV, so I'm not sure what tools you have available to upate a PV's trend chart. I'd expect to see timed and change-of-state.
June 3rd, 2002, 07:13 AM
Thanks Steve this is the kind of information i am looking for. Would rsveiw 32 work to display the graph assuming I can get the plc5 to record it in time
June 3rd, 2002, 10:25 AM
I have a solution but it would cost about 3K USD. It can gather 16 bit analog data the at 1024 times per second for up to 1 second at a time and it communicates very quickly with AB PLCs or HMIs over Etherent. It is ceritified Etherenet/IP.
June 5th, 2002, 10:04 AM
If you really need updates that fast you are trying to use the wrong tool for the job. You should probably be looking at a digital oscilloscope or National Instruments Labview software plus a high speed Data Acquisition card.
Are you sure your pressure transmitter is going to have that kind of response?
June 6th, 2002, 01:15 AM
They used the transducer to get a graph on a visitrack system. So I have been told. I am looking for a high speed plc just to track this one input. I may have to send it to a pc to monitor the graph. Thanks for the feedback.