Data Translation DT3000 Series, Руководство пользователя, Страница: 37 / 156

Chapter 3
36
Install jumpers W6 and W7 to connect DAC1 from the data acquisition board to channel 15 on
the 5B01 or 7BP16-1 backplane. Jumper W6 connects DAC0 to channel 15; jumper W7 connects
DAC1’s return.
Note: If you are using analog output modules on the 5B01or 7BP16-1 backplane, ensure that
you make no connections to the screw terminals corresponding to that signal on the screw
terminal panel. For example, if you are using channel 14 on the 5B01 for analog output, do
not use screw terminals corresponding to DAC0 on the screw terminal panel. You can read
the output of the DACs as inputs.
Resistors
Locations are provided on the DT730 and DT730-T for user-installed bias return and current
shunt resistors. (Resistors must be 1/4 W size.) The following subsections describe these
resistors and their use.
Configuring Resistors R1 to R32 - Input Bias Return
Differential mode permits low-level signal measurement by limiting common-mode input
noise. This mode provides a separate return path for each channel.
For floating signal sources, where the voltage source has no connection with earth ground,
you need to provide a bias return path by adding input bias return resistors. Input bias
resistors R1 through R32 connect the low sides of channels 0 to 31 to analog ground, where R1
corresponds to channel 0 and R32 corresponds to channel 31. When input bias resistors are
installed for an analog input channel, the high (or positive) side of the analog input channel
returns the source input impedance through the bias return resistor to the low side of the
channel, and then to analog ground.
Typical resistor values are 1 k
Ω
to 100 k
Ω
depending on the application. Refer to page 47 for an
example of using an input bias return resistor.
Configuring Resistors R33 to R64 - Current Shunt
In single-ended mode, inputs share a common return path. Single-ended connections should
be restricted to applications with high-level voltage inputs and short lead lengths.
Current shunt resistors R33 to R64 connect the high side of analog input channels 0 to 31 to the
low side of each input. Resistor R33 corresponds to analog input channel 0; resistor R64
corresponds to analog input channel 31. Current shunt resistors typically convert 4 to 20 mA
to 1 to 5 V for A/D conversion.
Note that, depending on your application, a bias current return resistor may also be required
in addition to the current shunt resistor.
The typical current shunt resistor value is 250
Ω.
If, for example, you add a 250
Ω
resistor to
location R33 and connect a 4 to 20 mA current loop input to channel 0, the input range for
channel 0 is converted to 1 to 5 V. Refer to
page 49 for an example of using a current shunt
resistor.
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