6
occurs, as when the power is initially applied, the response will
be critically damped. FIGURE 8 shows the response to a step
input.
After initial slewing at the maximum tracking rate of the convert-
er, there is one overshoot (which is inherent in a Type II servo).
The overshoot settling to final value is a function of the small sig-
nal settling time. For Velocity output, the simple filter shown in
FIGURE 9 will eliminate the one overshoot for step velocity input
and will filter the carrier frequency ripple.
ANALOG OUTPUTS
The analog outputs are velocity (VEL) and AC error (e). Both out-
puts can swing ±3.5 V min. with respect to V.
The AC error, e, is proportional to the error (
θ - φ) with a scaling
of 6.310 mV/LSB (14-bit mode), and 3.125 mV/LSB (16-bit
mode). Velocity output characteristics are listed in TABLE 4.
VELOCITY OUTPUT
The Velocity output (VEL) from the SD-14590 is a DC voltage
proportional to angular velocity d
θ/dt = dφ/dt. The velocity input is
the second integrator, as shown in FIGURE 6. Its linearity is
dependent solely on the linearity of the voltage controlled oscil-
lator (VCO). Due to the highly linearized VEL output, the electro-
mechanical tachometer can now be eliminated from motion con-
trol systems. Bandwidth (BW) and the acceleration constant (Ka)
can be determined from the formula shown:
BW(Hz) = BW(rad/sec)/2
π
Ka = A2
Outputs e and VEL are not required for normal operation of the
converter. V is used as an internal DC reference with the direct
input option. Maximum loading on V is 40k ohm; maximum load-
ing for e and VEL is 3k ohm. The velocity characteristics are
shown in TABLES 4 and 5. Output e is not closely controlled or
characterized. Consult the factory for further information.
FIGURES 10, 11, 12 are the synchro, resolver, and direct input
connection diagrams respectively.
OUTPUT
91k
VEL
(pin 23)
0.1 F
RC = 1/A
FIGURE 9. VELOCITY FILTER
-12
db/oct
4
BA
(BW)
2A
-6 db/oct
10B
ω (rad/sec)
OVERSHOOT
SMALL SIGNAL
SETTLING TIME
MAX SLOPE EQUALS
TRACKING RATE
(SLEW RATE)
θ2
θ1
SETTLING TIME
FIGURE 8. RESPONSE TO A STEP INPUT
FIGURE 7. OPEN LOOP BODE PLOT
TABLE 3. DYNAMIC CHARACTERISTICS
PARAMETER
UNITS
BANDWIDTH
400 HZ
60 HZ
RESOLUTION
Input Frequency
Tracking Rate
Bandwidth
Ka
A1
A2
A
B
acc-1 LSB lag
Settling Time
BITS
Hertz
RPS min
Hertz
1/sec2 nom
1/sec nom
Deg/sec2 nom
ms max
14
16
360-1000
10
2.5
54
*
12500
*
0.31
*
40k
*
112
*
52
*
275k
69
300
800
Note: * means the same as value to the left.
TABLE 4. VELOCITY CHARACTERISTICS
PARAMETER
UNITS
STANDARD
TYP
MAX
Polarity
Output Voltage
Voltage Scaling
Scale Factor
Scale Factor TC
Reversal Error
Reversal Error TC
Linearity
Linearity TC
Zero Offset
Zero Offset TC
Load
V
RPS
%
PPM/°C
%
PPM/°C
% output
PPM/°C
mV
V/°C
k Ohm
TABLE 5. VELOCITY VOLTAGE SCALING
BW
RESOLUTION (values in RPS/Volt)
14
16
Hl
LO
2.8
0.71
0.17
Note: If the resolution is changed while the input is changing, then the
velocity output voltage and the digital output will have a transient until
it settles to the new velocity scaling at a speed determined by the
bandwidth. If additional information is required, consult the factory.
14
16
47-1000
2.5
0.61
14
*
780
*
0.078
*
10k
*
28
*
13
*
17
4.3
1400
3400
Positive for increasing angle.
3.5
See Voltage Scaling Table 5.
10
15
100
200
12
25
50
12
25
50
15
35
25
50
-
3 min