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Please Note: Due to limitations in the IC, the high speed amplifier used in these devices may become unstable, exhibiting oscillations or negative output, if the power supply voltage is applied when the module is on. The unit should always be powered up using the power switch on the power supply or the unit itself. Hot plugging the unit is not recommended. http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=4&pn=PDA10CS