DMC developed a high-speed data acquisition system for a roll mill gauging system. Originally, wire thickness probes were connected to dedicated analog inputs on the Allen Bradley PLC. DMC found unacceptable levels of noise and slow and jittery sample rates that were characteristic of the PLC analog inputs. The objectives were to measure the wire thickness using an average of many samples, but to detect lumps at high frequency. Neither measurement was possible using the analog input channels of the AB PLC.
DMC solved the problem by eliminating the PLC’s analog inputs and the associated computation within the PLC program. We replaced this with an NI cRIO system. The system used NI’s isolated analog inputs to digitize the thickness probe’s signal at 80 kHz with low noise. Inside the cRIO’s FPGA, 16 samples at a time were averaged to decrease the signal frequency to 5 kHz and further reduce the noise that was seen with the AB PLC. The 5kHz signal was streamed to the cRIO’s real-time processor, where further filtering was applied. A low-pass filter determined the wire thickness measurement, while a high-pass filter monitored for lumps.
The cRIO sits on the machine’s Ethernet network and acts as an Ethernet/IP slave to Allen Bradley PLC. Wire thickness and lump detections are passed to the PLC at an appropriate rate.
Learn more about our Test and Measurement Automation expertise and contact us for your next project.