Wet Labs ac-s, Руководство пользователя

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34 ac-s User’s Guide (ac-s) Revision F 9 Feb. 2006
Appendix C: Common Mode A/C Induced Noise
The ac-s can be susceptible to common mode noise caused by environmental alternating
current (A/C) generated electromagnetic fields. Most typically, this will be caused by 60 Hz
A/C power wiring in a laboratory or ship environment. This noise can cause large
measurement errors in situations where the meter does not have an adequate earth ground.
Specifically, if a meter is powered from a battery or another “floating” power supply and is
feeding data to a laptop that is not connected to earth ground (powered via its own battery, or
ungrounded A/C adapter) this common mode noise will be most apparent. To eliminate this
noise issue, either the laptop, the power source, or the meter itself needs to be connected to
an earth ground (i.e. the ground receptacle of a wall outlet). Earth grounding for a power
supply should be made at the negative power connection to the meter. When grounding the
meter itself, any of the 10-24 socket cap screws on the unistrut yoke that support the zinc
anodes will suffice. Earth grounding for a laptop can generally be done via the metal
shielding around its serial port, parallel port or display connections. If an adequate earth
ground is not available in a shipboard environment, a wire to sea water should suffice. When
used in-situ, distance from A/C fields and earth grounding of the meter through immersion in
sea-water effectively eliminates this source of noise.