Hi All,
Background: I am developing an industry 4.0 power meter. I can measure the power consumption of the machine on one phase, it can calculate everything based on the measurements, and send everything to the server for further analysis.
Basics: I have done the field tests, and have found serious problems. You can see the problematic part of the schematic down below. S1 is a LEM HAIS50-P type hall-effect current transducer. U5 and the surrounding resistors form a subtractor amplifier, so the resulting voltage will be in the range of -0,635V - 0,635V (in case a -50A to +50A input current) and relative to the GND1 ground. This subtractor amp is required because the transducer outputs the voltage on a 2,5V reference potential.

Problem: I have connected the circuitry to the machine, one of the phases go through the current transducer. The whole device is powered from the line (L1 and neutral). Once the machine, that draws around 5 amps, is turned on, spikes generated between TP1 and TP2 test points. It seems that the transducer produces them. The problem is that they seems to be pretty huge, more than 20Vpp, while the power meter can tolerate 250mVpp. The IC seems have survived until now, but it will not live long I guess.

Here is one of those spike zoomed:

Question: How can I suppress these spikes? What kind of filter circuitry should I put to avoid them? Have you ever faced a problem like this? I should have visited the field earlier to investigate the behavior.
Thank you very much for your time.