Omron ZEN Operation Manual page 18

Precautions
Store the ZEN at an ambient temperature of −40 to 75°C for LED-type CPU Units
2.
and −20 to 75°C for all other types of CPU Units. If the ZEN has been stored at
−10°C or lower, allow it to stand at room temperature for 3 hours or longer before
turning ON the power supply.
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