Project: ESD and EMI cause production line quality issue

Timescale: One day factory visit

Scope of work: Identify whether the paint issue the company experienced is related to EMI or not, if yes, fix the issue.

The client is a manufacturing company which produces rulers. The problem on the production line was that when the paint injection machine started working, they found the paint on the ruler was not clear enough, with blurring images, etc. Together with this issue was that the computer which controls the machine often froze. Engineers on the production line said if they switched the lights off, they sometimes could see sparks in the dark.

This was a typical case in a factory site where ESD or EMI cause issues. We were often called by clients to solve similar issues. In this case, the fact that sparks were seen in the dark clearly indicated an ESD issue.

By using a handheld spectrum analyzer (mine works between 10 MHz and 6 GHz), we could generate a plot of the ambient noise. But for ESD events, the hand held spectrum analyzer wouldn’t capture it as the event occurred within 1 ns most of the time.

There are many ways of tracking an ESD event, in this case, we captured the event by using homemade current probe connected with a 1 GHz oscilloscope.

The fix is tricky. Although we captured the ESD event, but it is hard to trace the source within the given number of hours. But we were able to identify a few suspects shown below:

Figure 1. Potential stack charge build up areas

Once these suspected areas are identified, we then applied some fixes as shown in Figure 2.

Figure 2 Find way to dissipate the charge build up before they are built up

One of the anti-static products we recommended is shown below:

Figure 3 An anti-static brush that could be used for this problem

After the visit, we got feedback from the factory that the paint issue they were facing disappeared.