Question
Why does the DOSE-X collect charge even if there is no beam (beam-off)? Is the background or leakage current too high?
Answer
Zero drift
For reference class electrometers there is always a "zero drift". It is defined in the relevant norm IEC 60731 and must be ≤ 0.5% according to the IEC norm. The DOSE-X always achieves ≤ 0.5%.
Details
In order to estimate the zero-drift of a DOSE-X, the following test can be done:
Turn the device on and ensure a warm-up time of at least 15 minutes. Cover the connectors with the dust cap, no cables or chambers are connected to the device. Perform a background measurement and start a 60 seconds measurement directly afterwards with high voltage (HV) switched off.
Compare the measured current values (or the charge collected divided by the measurement time) to the following tolerances (0,5% of the corresponding sensitivity range):
- Low sensitivity the zero drift current should be less than 0.012nA (12pA)
- medium sensitivity zero drift current should be less than 0.030pA (30fA)
- high sensitivity the zero drift current should be less than 2fA
If the device exceeds these values, we recommend sending it in for a test and factory calibration. Please contact the support in such a case.
How can I contact the IBA Dosimetry Service and Support team?
Recommendation
It is always recommended to perform a background measurement directly before the dose or charge measurement itself.
Please mind: The zero drift is not included in the device's self-tests procedure.