AD2S90 データシートの表示（PDF） - Analog Devices

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AD2S90

Low Cost, Complete 12-Bit Resolver-to-Digital Converter

Analog Devices 

AD2S90

The small step response is given in Figure 20, and is the time

taken for the converter to settle to within 1 LSB.

ts = 7.00 ms (maximum)

The large step response (steps >20°) applies when the error

voltage will exceed the linear range of the converter. Typically it

will take three times longer to reach the first peak for a 179°

step.

In response to a velocity step [VELOUT/(dθ/dt)] the velocity

output will exhibit the same response characteristics as outlined

above.

10؇

0؇

0

4

8

12

16

20

Figure 20. Small Step Response

SOURCES OF ERROR

Acceleration Error

A tracking converter employing a Type 2 servo loop does not

suffer any velocity lag, however, there is an additional error due

to acceleration. This additional error can be defined using the

acceleration constant Ka of the converter.

Ka

=

Input

Error in

Acceleration

Output Angle

(10)

The numerator and denominator’s units must be consistent. Ka

does not define maximum input acceleration, only the error due to

its acceleration. The maximum acceleration allowable before the

converter loses track is dependent on the angular accuracy

requirements of the system.

Angular Error × Ka = degrees/sec2

(11)

Ka can be used to predict the output position error for a given

input acceleration. The AD2S90 has a fixed Ka = 3.0 × 106

sec–2 if we apply an input accelerating at 100 revs/sec2, the error

can be calculated as follows:

Input Acceleration LSB / sec 2

[ ] Error in LSBs =

[ ] Ka sec −2

[ ] [ ] 100 rev/ sec2 × 212 LSB /rev

=

[ ] 3.0 ×106 sec–2

= 0.14 LSBs

(12)

–10–

REV. D

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