AD598
–V
1 –V
S
2 EXC 1
3 EXC 2
4 LEV 1
0.015µF
5 LEV 2
6 FREQ 1
7 FREQ 2
8 B1 FILT
9 B2 FILT
0.1µF
10 V
B
MASTER
+V
S
20
OFFSET 1 19
OFFSET 2 18
SIG REF 17
82.5kΩ
SIG OUT 16
FEEDBACK 15
OUT FILT 14
A1 FILT 13
0.1µF
A2 FILT 12
V 11
A
0.33µF
0.1µF
5 LEV 2
6 FREQ 1
7 FREQ 2
8 B1 FILT
9 B2 FILT
10 V
B
SIG OUT 16
FEEDBACK 15
OUT FILT 14
A1 FILT 13
0.1µF
A2 FILT 12
V 11
A
0.33µF
0.1µF
+V
15k
–V
15k
SLAVE 1
1 –V
S
2 EXC 1
3 EXC 2
4 LEV 1
+V
S
20
OFFSET 1 19
OFFSET 2 18
SIG REF 17
82.5kΩ
5 LEV 2
6 FREQ 1
7 FREQ 2
8 B1 FILT
9 B2 FILT
10 V
B
SIG OUT 16
FEEDBACK 15
OUT FILT 14
A1 FILT 13
0.1µF
A2 FILT 12
V 11
A
0.33µF
+V
15k
–V
15k
SLAVE 2
1 –V
S
2 EXC 1
3 EXC 2
4 LEV 1
+V
S
20
OFFSET 1 19
OFFSET 2 18
SIG REF 17
82.5kΩ
+V
AD598
AD598
AD598
LVDT
SCHAEVITZ E 100
MECHANICAL POSITION INPUT
LVDT
SCHAEVITZ E 100
MECHANICAL POSITION INPUT
LVDT
SCHAEVITZ E 100
MECHANICAL POSITION INPUT
Figure 21. Multiple LVDTs—Synchronous Operation
HIGH RESOLUTION POSITION-TO-FREQUENCY
CIRCUIT
In the circuit shown in Figure 22, the AD598 is combined with
an AD652 voltage-to-frequency (V/F) converter to produce an
effective, simple data converter which can make high resolution
measurements.
This circuit transfers the signal from the LVDT to the V/F con-
verter in the form of a current, thus eliminating the errors nor-
mally caused by the offset voltage of the V/F converter. The V/F
converter offset voltage is normally the largest source of error in
–Vs
GND
0.1µF
0.1µF
+Vs
such circuits. The analog input signal to the AD652 is converted
to digital frequency output pulses which can be counted by
simple digital means.
This circuit is particularly useful if there is a large degree of
mechanical vibration (hum) on the position to be measured.
The hum may be completely rejected by counting the digital fre-
quency pulses over a gate time (fixed period) equal to a multiple
of the hum period. For the effects of the hum to be completely
rejected, the hum must be a periodic signal.
1 +V
S
1 –V
S
2 EXC 1
3 EXC 2
4 LEV 1
0.015µF
5 LEV 2
6 FREQ 1
7 FREQ 2
8 B1 FILT
9 B2 FILT
0.1µF
10 V
B
+V
S
20
OFFSET 1 19
OFFSET 2 18
SIG REF 17
SIG OUT 16
FEEDBACK 15
0.33µF
OUT FILT 14
A1 FILT 13
0.1µF
A2 FILT 12
V 11
A
8
–V
S
0.02µF
5
6
OP AMP “–”
OP AMP “+”
2
3
4
TRIM
TRIM
OP AMP OUT
AD652
SYNCHRONOUS
VOLTAGE TO
FREQUENCY
CONVERTER
COMP REF 16
COMP“+” 15
COMP“–” 14
ANALOG GND 13
DIGITAL GND 12
FREQ OUT 11
CLOCK INPUT 10
500KHZ
C
OS
9
+V
S
2.5k
+V
S
FREQ
OUT
7 10 VOLT INPUT
CK
AD598
LVDT
SCHAEVITZ E 100
MECHANICAL POSITION INPUT
Figure 22. High Resolution Position-to-Frequency Converter
REV. A
–11–
AD [ ANALOG DEVICES ]
