National Instruments 320174B-01 用户手册

                                                                                                                     

This appendix lists the specifications of the Lab-NB.  These specifications are typical at 25° C unless otherwise
stated.  The operating temperature range is 0° to 70° C.

Number of input channels........................................................8 single-ended
Analog resolution........................................................................12 bits, one part in 4,096
Relative accuracy (nonlinearity) ...........................................±1.5 LSB max,

(nonlinearity + quantization error;...............................±1.0 LSB typ
see explanation of specifications)

Differential nonlinearity...........................................................±1.0 LSB max (no missing codes),

±0.5 LSB typ

Analog input range.....................................................................±5 V or 0 to +10 V; jumper-selectable
Input signal gain..........................................................................1, 2, 5, 10, 20, 50, 100; software-selectable
Measurement (gain) accuracy

gain = 1 ..................................................................................±0.04% max,

±0.025% typ

Offset error

(calibration performed at gain = 1)
gain 

≤

 20................................................................................±4 LSB max, ±2 LSB typ

gain > 20................................................................................±20 LSB max, ±10 LSB typ

Offset adjustment range, min

(unipolar or bipolar ranges)............................................±47 LSB

Gain adjustment range, min

(unipolar or bipolar ranges)............................................±31 LSB

System noise .................................................................................0.3 LSB rms for gain = 1

0.6 LSB rms for gain = 100

Temperature coefficients

Gain error..............................................................................±10 ppm/°C
Offset error ...........................................................................450 µV/°C + 10 µV/°C * gain

Input bias current ........................................................................150 pA
Input impedance ..........................................................................0.1 G

Ω

 in parallel with 45 pF

Input protection............................................................................±45 V on all inputs (not ground)

Relative accuracy is a measure of the linearity of an ADC.  However, relative accuracy is a tighter specification than
a nonlinearity specification.  Relative accuracy indicates the maximum deviation from a straight line for the analog-
input-to-digital-output transfer curve.  If an ADC has been calibrated perfectly, then this straight line is the ideal
transfer function, and the relative accuracy specification indicates the worst deviation from the ideal that the ADC
permits.

A relative accuracy specification of ±1 LSB is roughly equivalent to (but not the same as) a ±1/2 LSB nonlinearity
or integral nonlinearity specification because relative accuracy encompasses both nonlinearity and variable

quantization uncertainty, a quantity often mistakenly assumed to be exactly ±1/2 LSB.  Although quantization

uncertainty is ideally ±1/2 LSB, it can be different for each possible digital code and is actually the analog width of
each code.  Thus, it is more specific to use relative accuracy as a measure of linearity than it is to use what is