Voltmeter drift caused errors in measurements.

Different voltmeters were used for Hall probe calibration and measurements on Kugler bench 
before March 2011. We have found that voltmeters drifted differently in time. The difference resulted in errors in magnetic field measurements. March 2011 we used the same voltmeter for probe calibration and measurements of the reference undulator. The results showed difference in K = 2.8*10-4, which correspondes to 406 microns shift of magnetic axis in x-direction, i.e. fiducialization data in x-direction were wrong for all undulators measured and tuned before March 2011 (see "K_calculation.xls" worksheet). 
To keep future undulator measurements consistent with the previous measurements a shift of 406 microns will be added to the future fiducialization data (see "Calculation.xls" worksheet).

by Yurii Levashov,
03/17/2011

On 12/01/2012 the Reference undulator experienced temperature change down to 18 degrees C. It resulted in field integrals change. The K change is insignificant (< 5*10-5).

by Yurii Levashov
01/22/2013