Data Translation DT300 Series, User Manual

Page: 36 / 164

Chapter 3
36
Configuring Resistors on the STP300
Locations are provided on the STP300 screw terminal panel for installing bias return and
current shunt resistors. The following subsections describe how to configure these resistors.
Configuring Resistors R1 to R8 - Bias Return
Resistor locations R1 to R8 connect the low side of analog input channels to analog ground.
These resistor locations are typically used when connecting differential inputs to analog input
channels 0 to 7, where R1 corresponds to analog input channel 0 and R8 corresponds to analog
input channel 7.
The high side of the corresponding analog input channel returns the source input impedance
through the bias return resistors to the low side of the channels, and then to analog ground.
Typical resistor values are 1 k
Ω
to 100 k
Ω
depending on the application. Refer to page 49 for an
example of using bias return resistors with differential inputs.
Configuring Resistors R9 to R16 - Current Shunt
Resistor locations R9 to R16 are typically used to convert current to voltage on channels 0 to 7,
where R9 corresponds to analog input channel 0 and R16 corresponds to analog input channel
7.
The resistor location connects the high side of the channel to the low side of the corresponding
channel, thereby acting as a shunt. If, for example, you add a 250
Ω
resistor to location R9, and
then connect a 4 to 20 mA current loop input to channel 0, the input range is converted to 1 to
5 V. Note that, depending on your application, you may need to use resistors R1 to R8 with
resistors R9 to R16 for proper operation. Refer to
page 50 for an example of using current
shunt resistors with current loop inputs.