National Instruments 7340 PCI

Chapter 5 Signal Connections

You can configure each ADC channel for motion feedback, simple

A/D conversion, or both.

You can read the digital value of analog voltage on any of the eight

ADC channels of the controller. Table 5-3 shows the range of values

read back and the voltage resolution for each setting. The voltage

resolution is in volts per least significant bit (V/LSB).

As indicated in Figure 5-3, when configured as analog feedback, an

analog sensor acts like a limited range absolute position device with a

full-scale position range. You can map any ADC channel as feedback

to any axis.

You can enable and disable individual ADC channels in software.

Disable unused ADC channels for the highest multiplexer scan rate

performance. Properly enabled, the scan rate is high enough to support

analog feedback at the highest PID sample rate.

• Analog Reference—For convenience, 7.5 V (nominal) analog

reference voltage is available. You can use this output as a low-current

supply to sensors that require a stable reference. Refer to Appendix A,

Specifications, for analog reference voltage specifications.

• Analog Input Ground—To help keep digital noise out of the analog

input, a separate return connection is available. Use this reference

ground connection and not Digital Ground (digital I/O reference) or

Analog Output Ground as the reference for the analog inputs.

Wiring Concerns

For proper use of each ADC input channel, the analog signal to be

measured should be connected to the channel input and its ground reference

connected to the Analog Input Ground.

Note The analog reference output is an output signal only and must not connect to an

external reference voltage. Connect the common of the external reference to the Analog

Input Ground pin for proper A/D reference and improved voltage measurement.

Table 5-3. Analog Input Voltage Ranges

Input Range Binary Values Resolution

±10 V –2,048 to 2,047 0.0049 V/LSB

±5V –2,048 to 2,047 0.0024 V/LSB

0–10 V 0 to 4,095 0.0024V/LSB

0–5 V 0 to 4,095 0.0012V/LSB