Kiet, Robert, and Carlos

We report the results of calibrating the LEMI magnetometers in the Vault outside of the X arm; 

We went out on May 15th, 2025 and took the following measurement with each lasted 2 minutes.
Far field injection: to calibrate the LEMI 

1) 17:36:45 UTC; X-axis far-field injection; without preamp on the Bartington 

2) 17:43:23 UTC; X-axis far-field injection; without preamp on the Bartington 

3) 18:01:53 UTC, X-axis far-field injection; without preamp on the Bartington 

4) 18:04:15 UTC, X-axis far-field injection; without preamp on the Bartington 

5) 18:23:25 UTC; Y-axis far-field injection; with preamp on the Bartington 

6) 18:26:00 UTC; Y-axis far-field injection; with preamp on the Bartington 

The preamp gain is 20; all injections are done at 20Hz. The coil used for far field injection has 26 turns, 3.2 Ohms.

The voltage that was used to drive the injection coil for farfield injection: Vp-p: 13.2 +- 0.1V. It was windy out so we decided to use the preamp on the Bartington magnetometer.
The LEMI channels used for this analysis: H1:PEM-VAULT_MAG_1030X195Y_COIL_X_DQ; H1:PEM-VAULT_MAG_1030X195Y_COIL_Y_DQ

Bartington calibration

7) 18:49:38 UTC; with preamp on the Bartington 

8) 18:52:50 UTC;  with preamp on the Bartington 
the voltage that was used to drive the injection coil for farfield injection: Vp-p: 1.88V +- 0.01V 
We inserted the bartington magnetometer to the center of a cylindrical coil to calibrate its z axis(1000 Ohms, 55 turns in 0.087 m) 

The final results of LEMI calibration after taken accound the all the measurements is (9.101 +- 0.210)*10^-13 Tesla/counts, there is a 20% difference between this measurement and the measurement taken pre O3. Robert noted that when taking the previous measurements, the calibrating magnetometer was not fully isolated from the LEMI. This time they are completely independent.

We recommend analyses that use LEMI data to use the calibration value of  9.101 * 10^-13 +- 5% Tesla/counts to be consersative.