Photodiodes used in beam monitoring.

Another way for counting and monitoring when we have to measure very high flux is by using diodes and measuring the current which is produced by irradiation. This weak current is measured with a picoamperemeter from Novelec (a local company, F38240 Meylan, 33-4-7690-7045) the value is then converted into frequency wich is read through the same acquisition card than the PM.

  |  Picoamperemeter    |      real flux per count       | 
  |  Channel |  output  |          | 
  |          |   A/V    |   0.5 A  |   1.0 A  |   1.5 A  | 
  |     1    |  1e-08   |
  |     2    |  1e-09   |
  |     3    |  1e-10   |

With the MCCE picoamperemeter (October 1997) from Novelec, the channel has been changed to increase the sensitivity. The counts are always read through the same acquisition card (ESRF Vct6) but an offset of (1e6 ct/s) has to be removed if raw values are read. Note than frequency above 1e6 counts/s are not reliable, there is a residual offset of some 1e2 counts/s which can be adjusted.