The aim of this procedure is the correlation of the values of the beamline diodes (I0, I1) with those of previously calibrated diodes. The outcome is to calculate – and eventually display in MxCuBE - the beam-line flux (photons/sec) at all wavelengths. The calibrated diodes and other ancillary equipment required are available from the MX BLOMs


1. Note the number (1 to 5) of the calibrated diode being used in the procedure.

2. Align the calibrated diode in the X-ray beam (see below).

3. Connect the calibrated diode to a Keithley pico-ampmeter (see below).

4. Connect the Kiethley to the GPIB device (see below). GPIBs are already available on ID23 and ID29. For ID14  a GPIB is supplied with the calibrated diode and Keithley

5. Set up a counter in SPEC (EXP) for this Keithley (see below, you may need to ask your BLISS Contact to do this).

6. Search the experimental and optics hutches

7. Open the front end and the safety shutter

8. Remove back-light, scintillator and beam-stop from the X-ray beam path

Automatic Calibration

1. Start the SPEC session BLCAL on the lid on which the SPEC session EXP runs (i.e. lid292 etc). This session includes the macros fluxcalibration.mac, blcal.mac and the python script ( used by the calculation server.

2. In the BLCAL spec session type, for calibrated diode n:

flux_do_calibration n

The resulting calibration procedure is then carried out. This could take some time and depends on  the number of energies at which the calibration is carried out (the energies are selected automatically using the configuration files of mxCuBE).

The results are recorded in the file:


which is used by SPEC (EXP) to compute the photon flux.

Manual Calibration

This should not normally be necessary. However, the procedure is noted here for completeness. After the preparation step, for each wavelength desired:

1. Set the transmission to 100% and open the beam-defining slits until I1 and/or I0 are saturated

2. Measure & note:
       The current measured on the calibrated diode
       The counts on I0 and I1 and their respective gains
       Slit sizes (optional)
       Beam transmission values (optional)
       Machine current (optional)

3. Change the value of beam-transmission and/or slit size

4. Repeat step 2

Once all measurements have been carried out enter these into the beam-line specific excel sheet and use this to convert them into photon flux. You can then calculate a linear regression relating flux to beamline diode readings and put the result in the setup file for SPEC (EXP).


Installing the calibrated diode, Kiethley and GPIB

1. Positioning the calibrated diode. A magnetic holder is available to position the diode in the beam path as close  to the sample position as possible. In order to align it easily, the backlight can be use to set the position of the diode. Be careful when positioning the diode and the magnetic holder in order to avoid any collision with either the back light or the detector. Also check that the calibrated diode is as perpendicular to the beam path as possible.


2. Connecting the diode, Keithley and GPIB.  Depending on the length of the cable available, the Keithley can be installed either on the mini- or micro-diffractometer or on the marble of the experimental table. This should then be connected to the the calibrated diode. 

Important: Check that the Keithley is not using the Z transform of the incoming signal.


Using a GPIB Agilent 10833C cable, connect the Keithley to the GPIB, connect the GPIB power supply and then connect the GPIB to the appropriate network connection. Ask your BLISS contact to configure it in the corresponding SPEC session. You are now ready to display the diode measurements in SPEC.