Inboard (X1A2) exit slit calibration

The inboard (X1A2) exit slit width in microns was measured as a function of motor steps. The data is stored in the file exsi_cal.map, which can be found in the local/x1 CVS repository of IDL program files. We fit the slit width $m$ as a function of motor steps $s$ by a parabola, that has the origin on the x axis:

$$m=A[1]*(s-A[0])^2,$$ (3.5)

where $A[0]$ is the shift of the origin of the parabola from the origin (in motor steps) and $A[1]$ is the opening of the parabola. At the same we may measure the signal $p$ seen on the shutter photodiode and fit it to the corresponding expression:

$$p=B[1]*(s\prime-B[0])^2$$ (3.6)

The difference $A[0]-B[0]$ gives the shift in motor steps of the measurement in respect to the calibration. This shift should be compensated for so that equation 3.5 can be used to calculate the slit width and motor positions. The motor position corresponding to a given slit width can be obtained by inverting equation 3.5:

$$s=A[0]-\sqrt{m \over{A[1]}}$$ (3.7)

For fitting use the routine exsi_cal.pro, which can be found in the local/x1 CVS repository. Fig. 3.24 shows the shutter photodiode signal as a function of motor steps. Note that the region where the signal is 0 has been trimmed off. Create a similar measurement and save your trimmed data. Fig. 3.25 shows the calibration plot (X markers) with fit and the fitted shutter photodiode measurement (triangle markers). It has been created by calling:

  IDL> exsi_cal,'/mnt/x1a/x1a_13jan2002_0001.csv'

where you have to replace the file name with your file name.

Figure 3.24: Inboard exit slit calibration: signal of inboard (X1A2) shutter photodiode as a function of inboard (X1A2) exit slit EXS_I motor position.

Figure 3.25: Fitting inboard exit slit measurements. Inboard (X1A2) exit slit EXS_I calibration fit. X mark the calibration data, triangles mark the fitted shutter diode signal. Lines mark the fitted parabolas. They all lie reasonably well on top of each other.