Dataq DI-710 Series, Руководство пользователя

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DI–710 Series and DI-715B Series Hardware Manual
Accessories
48
Isolated Signal Sources
There are two considerations when connecting a differential amplifier to an isolated signal source: The elimination of
ground loops as described above, and the use of bias resistors to provide bias current for the differential amplifier's
positive and negative inputs.
The bias resistors should be chosen to be as low as possible, but the value you use is dependent upon the output
impedance of your signal source. Generally, the value of the bias resistor should be 10 times the output impedance of
your signal source or higher. Bias resistors greater than 1M
Ω
are not recommended.
Signal Cable and the Differential Amplifier
Quick rule-of-thumb: Any application requiring a differential amplifier also defines a need for quality signal cable.
Four elements combine to ensure adequate quality signal cable: a twisted signal pair with low resistance stranded
copper conductors; surrounded by a multiple-folded foil shield; with a copper stranded drain wire; all contained
within an insulated outer jacket.
In applications where such signal cable is used, a dramatic decrease in noise pickup will be experienced. The drain
wire should be considered as the shield and should be connected as described in “Connecting a Differential Ampli-
fier” on page 46. Signal cable meeting all four criteria for quality is Belden No. 8641.
+
Floating
Signal
Source
Differential
Amplifier
-
gnd
Signal
Lead
Shield
DI-205 terminal strip
Locate bias resistors as close
to amplifier as possible
Insulated Outer Jacket
Foil Shield
Drain Wire
Twisted Signal Pair
Stranded Copper Conductors