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NI 9752 User Manual
Active Inputs / Potentiometer Inputs
Figure 4 shows the analog input circuit configuration for both active-drive analog sensors and
potentiometers for measuring voltages from 0 V to 5 V. This is the standard configuration for
Channels 4 through 16 in the NI 9752. Channels with this configuration are protected from
voltage swings of ±30 V.
This circuit utilizes a weak pull-down for open circuit detection. If the channel is connected to
a potentiometer, the pull-down slightly modifies the voltage the A/D converter receives. You
must perform a full potentiometer calibration because the voltage from this circuit does not
readily correlate to the voltage resulting from an input circuit without a pull-down.
Examples of potentiometers are throttle position and pedal position sensors.
Figure 4.
Analog Input Configuration for Active Sensors and Potentiometers
Thermistor Inputs / Switch Inputs
Figure 5 shows the analog input circuit configuration for thermistors and switches to measure
voltages from 0 V to 5 V. This is standard configuration for Channels 17 through 21 in the
NI 9752. Channels with this configuration are protected from voltage swings of ±30 V.
Thermistor inputs have a strong pull-up to create a voltage divider with the sensor. Refer to the
sensor datasheet for sensor resistance curves. Most production automotive temperature sensors
are thermistors with a maximum cold resistance of approximately 100 k
Ω
and a resistance of
approximately 100
Ω
at 150 °C. The pull-up resistor of 1 k
Ω
provides a usable output voltage
range for thermistors of this type.
When used as a switch input, the switch must short to ground when it is closed.
