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If a HyD does shut down you won't see anything on the screen except if you have the Glow Over/Under look-up table applied. In the latter case the image will be totally green because every value will be zero. To reactivate the detector you can simply uncheck and check the Active check box in the detector controls (Figure 1)
Interference - switch mobile phones off
You must switch off mobile phones, put them into flight mode or otherwise make them incapable of sending or receiving signals when in room 1.20B with the SP5. This is because the HyD detectors pick up mobile phone signals as interference lines on the scan. There is a sticker on the door to remind you of this.