"I hava a 4-20 mA sensor connected to a PLC Analog current input. The scan time for the input is 30ms.
If i connect a highspeed data aquizition system(1ms) in serial with my sensor+PLC AI will the scan time of the PLC AI affect the max speed that i can collect data in my data aquizition system?"
The current signal will always be there. The signal is NOT interrupted for sampling or reading.
On the PLC side...
The Analog Input Module takes a certain amount of time to convert the current signal to a digital value. At the end of that time, the Analog Input Module leaves the latest converted analog-to-digital value in a "drop-box" (memory location).
The value in the drop-box is updated at whatever speed the Analog Module can make conversions.
The PLC "reads" the contents of the drop-box at whatever rate it can. This means, the PLC might read the same value several times before the value is updated by the Analog Module. In this case, the PLC has a short scan time relative to the Analog Module conversion time.
Or, the value might be updated by the Analog Module several times before the PLC finally gets around to reading it. In this case, the PLC has a long scan time relative to the Analog Module conversion time.
On the data aquisition system side...
Again, the current signal will always be there. The signal is NOT interrupted for sampling or reading.
It will convert the analog signal as quickly as it can and log it into a data-base or whatever.
The point is, this configuration is exactly the same as place two different flow meters, one reading in Gallons-per-Minute, and one reading Gallons-per-Hour, right next to each other in a stream.
Neither interferes with the other and the reading on each is only as up-to-date as the particular timing/resolution allows.
