AD2S82 AD [Analog Devices], AD2S82 Datasheet - Page 13

• Manufacturer Part Number: AD2S82
• Description: Variable Resolution, Monolithic Resolver-to-Digital Converters
• Manufacturer: AD [Analog Devices]

REV. B
The small signal step response is shown in Figure 8. The time
from the step to the first peak is t
the step until the converter is settled to 1 LSB. The times t
t
where R = resolution, i.e., 10, 12, 14 or 16.
The large signal step response (for steps greater than 5 degrees)
applies when the error voltage exceeds the linear range of the
converter.
Typically the converter will take three times longer to reach the
first peak for a 179 degrees step.
In response to a velocity step, the velocity output will exhibit
the same time response characteristics as outlined above for the
position output.
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 K
The numerator and denominator must have consistent angular
units. For example, if K
may be specified in degrees/sec
Angular measurement may also be specified using radians, min-
utes of arc, LSBs, etc.
K
to it’s acceleration. The maximum acceleration allowable before
the converter loses track is dependent on the angular accuracy
requirements of the system.
K
input acceleration. For example for an acceleration of 100 revs/
sec
2
A
A
are given approximately by
2
does not define maximum input acceleration, only the error due
can be used to predict the output position error for a given
, K
Figure 8. AD2S81A/AD2S82A Small Step Response
A
POSITION
OUTPUT
= 2.7
Angular Accuracy
10
6
K
sec
t
1
A
A
A
–2
t
of the converter.
2
is in sec
and 12-bit resolution.
Error in Output Angle
t
1
Input Acceleration
f
BW
2
5
t
f
and the error output in degrees.
2
1
BW
1
–2
K
and the t
, then the input acceleration
A
12
R
= degrees/sec
TIME
2
is the time from
2
1
and
–13–
To determine the value of K
used to define the dynamics of the converter, the following
should be used:
Where n = resolution of the converter
SOURCES OF ERRORS
Integrator Offset
Additional inaccuracies in the conversion of the resolver signals
will result from an offset at the input to the integrator as it will
be treated as an error signal. This error will typically be 1 arc
minute over the operating temperature range.
A description of how to adjust from zero offset is given in the
Component Selection section and the circuit required is shown
in Figures 1a and 1b.
Differential Phase Shift
Phase shift between the sine and cosine signals from the resolver
is known as differential phase shift and can cause static error.
Some differential phase shift will be present on all resolvers as a
result of coupling. A small resolver residual voltage (quadrature
voltage) indicates a small differential phase shift. Additional
phase shift can be introduced if the sine channel wires and the
cosine channel wires are treated differently. For instance, differ-
ent cable lengths or different loads could cause differential
phase shift.
The additional error caused by differential phase shift on the
input signals approximates to
This error can be minimized by choosing a resolver with a small
residual voltage, ensuring that the sine and cosine signals are
handled identically and removing the reference phase shift (see
Connecting the Resolver section). By taking these precautions
the extra error can be made insignificant.
Under static operating conditions phase shift between the refer-
ence and the signal lines alone will not theoretically affect the
converter’s static accuracy.
However, most resolvers exhibit a phase shift between the signal
and the reference. This phase shift will give rise under dynamic
conditions to an additional error defined by:
where a = differential phase shift (degrees).
Shaft Speed (rps) Phase Shift (Degrees )
100
Error = 0.53 a
b = signal to reference phase shift (degrees).
Error in LSBs
[
rev
R4, R6 in ohms
C5, C4 in farads
2 7 10
.
/
sec
Reference Frequency
K
2
]
A
6
2
12
2
n
b arc minutes
Input Acceleration LSB
0 15
R6 R4 (C4
A
.
4.04 10
AD2S81A/AD2S82A
based on the passive components
LSBs or
K
A
[
sec
11
47 5
–
2
[
.
C5)
]
seconds
/
sec
2
]
of arc