DETMON: Investigate occasional strange values on HVCAENA IOC

As someone supporting the detectors at ISIS, I would like to monitor HVCAEN crates without having occasional strange values. It is suspected that this is a reading fault. An example of the strange values can be seen in the file at `shares\ISIS_Experiment_Controls\data for tickets\Ticket6746_detmon_investigate_strange_values`. In nexus file 443 entry 105 of SANS2D_01_TEMP is 1.85E9. There are a few more of these values in the voltages and currents.

## Acceptance criteria

- [ ] Reason for the occasional strange values is established and fixed
- [ ] Fix is reported to Davide