User manual

Chapter 3 Hardware Overview

Input Range

The NI 6034E/6035E/6036E device has a bipolar input range that changes

with the programmed gain. Each channel may be programmed with a

unique gain of 0.5, 1.0, 10, or 100 to maximize the 16-bit analog-to-digital

converter (ADC) resolution. With the proper gain setting, you can use the

full resolution of the ADC to measure the input signal. Table 3-2 shows the

input range and precision according to the gain used.

Scanning Multiple Channels

The devices can scan multiple channels at the same maximum rate as their

single-channel rate; however, pay careful attention to the settling times for

each of the devices. No extra settling time is necessary between channels

as long as the gain is constant and source impedances are low. Refer to

Appendix A, Specifications, for a complete listing of settling times for each

of the devices.

When scanning among channels at various gains, the settling times may

increase. When the PGIA switches to a higher gain, the signal on the

previous channel may be well outside the new, smaller range. For instance,

suppose a 4 V signal is connected to channel 0 and a 1 mV signal is

connected to channel 1, and suppose the PGIA is programmed to apply

a gain of one to channel 0 and a gain of 100 to channel 1. When the

multiplexer switches to channel 1 and the PGIA switches to a gain of 100,

the new full-scale range is ±50 mV.

The approximately 4 V step from 4 V to 1 mV is 4,000% of the new

full-scale range. It may take as long as 100 µs for the circuitry to settle to

1 LSB after such a large transition. In general, this extra settling time is not

needed when the PGIA is switching to a lower gain.

Table 3-2. Measurement Precision

Gain Input Range Precision

0.5

–

10 to +10 V 305.2 µV

1.0

–

5to+5V 152.6 µV

10.0

–

500 to +500 mV 15.3 µV

100.0

–

50 to +50 mV 1.53 µV

* The value of 1 least significant bit (LSB) of the 16-bit ADC; that is, the voltage

increment corresponding to a change of one count in the ADC 16-bit count.

Note: See Appendix A, Specifications, for absolute maximum ratings.

UM.book Page 3 Monday, May 14, 2001 10:32 AM