This week at BSC8, the actuators were connected to the boots. We started to test the HEPI. First, we had to change a horizontal L4C in corner 2 (bad behavior at low frequency). We replaced L41375 by L41499. ASDs confirmed that this new geophone is working fine

After few static tests, we quickly found that the displacement created by the horizontal actuators in corner 2 is not as large as displacements created by the other horizontal actuators (verified with the dial indicators and the IPS). We checked the stops and nothing seemed to be touching. Then, we performed the linearity-hysteresis test for all 8 actuators (attached plots. SUS watchdogs tripped during the measurements – Visible on V3). The plots confirm that there is a trouble in the horizontal direction in corner 2. We are investigating.