E852 Documentation: MPS Magnet

MPS Magnet Map

The documentation on the MPS magnet map is here.

MPS Magnet Calibration

The following note gives the calibration of the CAMAC DVM (GROUP_DVMS, channel 3, counting from 1) with respect to the MPS DVM located at the MPS magnet control station. The calibration of the MPS magnetic field with respect to the MPS DVM is given in the MPS magnet operation note by Asher Etkin.

From olchansk@loki.ags.bnl.gov  Fri May 20 04:11:14 1994
Date: Fri, 20 May 94 04:11:13 -0400
From: olchansk@loki.ags.bnl.gov (Konstantin Olchanski)
To: ostrov@loki.ags.bnl.gov, olchansk@loki.ags.bnl.gov,
        weygand@loki.ags.bnl.gov
Subject: dvm calibration

Dennis, Sasha:

I redid the DVM calibration: the calibration is the following:

(DVM by the MPS magnet control) = 0.000244742 * (CAMAC DVM) + 0.0002026

the method used to calibrate the DVMs was:
turn the magnet on, wait for the DVM readings to settle, record them,
readout the CAMAC DVM with the DAQ, record the reading of the CAMAC DVM.

The obtained data is:

MPS DVM      CAMAC DVM

0.000408    0
0.2260    924
0.4246   1735
0.4776   1949
0.4924   2011
0.4987   2037

The fit was made using pvwave.

This result is different from the calibration used in the current E852
code (file Tracking/mpsMagnet.c). The calibration used in the code is:

      V = 0.0002444 * (float) dvm->adc[2].value - 0.0003;
      /* We believe dvm is 1 millivolt down - add it here */
      V += .001;

Notice the 0.001 volt difference in the calibration.

At full field (DVM=0.4937), the difference is 0.001/0.4937 = 0.2%, which
corresponds to 36 MeV shift in the momentum.

Const