Keithley KPCI-3101 Series, User Manual

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KPCI-3101 — KPCI-3104 Series User’s Manual Installation and Configuration 3-11
Resistors
Locations are provided on the STA-300 screw terminal panel for installing bias return and cur-
rent shunt resistors. The following subsections describe these resistors and their use.
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, then to analog ground. Typical
resistor values are 1k
Ω
to 100k
Ω
depending on the application. Refer to Figure 3-7 on page 3-17
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, then
connect a 4 to 20mA current loop input to channel 0, the input range is converted to 1 to 5V.
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
Figure 3-9 on page 3-18 for an example of using cur-
rent shunt resistors with current loop inputs.
Screw terminal assignments
With the connector held up, the screw terminals on the right side of the STA-300 match pins 23
to 34 and pins 57 to 68 of the standard 68-pin connector on the KPCI-3101–4 Series boards;
these screw terminals represent the analog I/O signal connections. The remaining screw termi-
nals are located on the left side of the STA-300 screw terminal panel and are provided for the
digital I/O, counter/timer, and +5V power signals.
The following subsections describe the screw terminal assignments on the STA-300 screw ter-
minal panel by function.