Capturing Intermittent Abnormal Drive SCR Firing
Whether dealing with legacy or modern digital drives, it is what is being fed from the drive output to the motors that counts as this is what will affect the process and product quality.
The quality of the drive motor current output relies on a good operation of the rectifier bridge which is composed of SCRs. These receive a precise firing sequence which occurs at a high frequency rate.
Although some drives will display an error message indicating a misfiring of the SCRs, a high frequency data acquisition is mandatory for further investigation to analyse the issue and determine specific corrective actions.
On one of the tissue machine which has our constant attention through 90 kpis we calculate every hour, our specialists were alerted of abnormal armature current variations in the reel motor. Having high resolution data (2,500 samples/sec) allowed us to discover that while the drive AC supply was stable, there was misfiring of the drive SCRs.
Our specialists contacted the mill and sent a detailed report with recommendations to check the reel drive firing card.
The mill located a spare firing card and proceeded with its replacement. Following this intervention, we confirmed that the issue has been solved.
Having high resolution quality data continuously analyzed enabled quick detection and precise diagnostic which translated in major savings in terms of product quality and eventual drive failure.
This would have led to significant downtime and several unnecessary replacements exposing the mill to new risks.