AD598 Analog Devices, AD598 Datasheet - Page 11

• Manufacturer Part Number: AD598
• Description: LVDT Signal Conditioner
• Manufacturer: Analog Devices

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
REV. A
0.015 F
0.1 F
– V
0.015 F
10
8
1
2
3
4
5
6
7
9
0.1 F
– Vs
LEV 2
EXC 1
EXC 2
LEV 1
FREQ 1
FREQ 2
B1 FILT
B2 FILT
V
–V
B
SCHAEVITZ E 100
MECHANICAL POSITION INPUT
S
10
8
1
2
3
4
5
6
7
9
0.1 F
AD598
MASTER
EXC 1
EXC 2
LEV 1
LEV 2
FREQ 1
FREQ 2
B1 FILT
B2 FILT
–V
V
FEEDBACK
B
SCHAEVITZ E 100
MECHANICAL POSITION INPUT
OFFSET 2
S
OFFSET 1
OUT FILT
SIG OUT
SIG REF
A1 FILT
A2 FILT
AD598
+V
GND
V
FEEDBACK
A
S
OFFSET 2
OFFSET 1
OUT FILT
19
18
16
14
13
12
20
17
15
11
SIG OUT
Figure 22. High Resolution Position-to-Frequency Converter
SIG REF
A1 FILT
A2 FILT
LVDT
82.5k
+V
+V
Figure 21. Multiple LVDTs—Synchronous Operation
V
0.33 F
0.1 F
A
S
0.1 F
13
12
20
19
18
17
16
15
14
11
LVDT
+ Vs
15k
0.33 F
0.1 F
0.1 F
15k
– V
10
2
3
4
5
6
7
8
9
1
0.02 F
EXC 1
EXC 2
LEV 1
LEV 2
FREQ 1
FREQ 2
B1 FILT
B2 FILT
–V
V
B
SCHAEVITZ E 100
MECHANICAL POSITION INPUT
S
AD598
SLAVE 1
–11–
FEEDBACK
OFFSET 2
OFFSET 1
OUT FILT
SIG OUT
SIG REF
A1 FILT
A2 FILT
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
2
3
4
5
6
7
8
10 VOLT INPUT
+V
+V
TRIM
TRIM
OP AMP OUT
OP AMP “–”
OP AMP “+”
–V
V
A
S
S
S
19
18
17
16
14
13
12
20
15
11
LVDT
82.5k
+V
0.33 F
0.1 F
SYNCHRONOUS
VOLTAGE TO
FREQUENCY
CONVERTER
AD652
15k
0.1 F
15k
– V
ANALOG GND
CLOCK INPUT
DIGITAL GND
10
2
3
4
5
6
7
8
9
COMP REF
1
FREQ OUT
COMP“+”
COMP“–”
EXC 1
EXC 2
LEV 1
LEV 2
FREQ 1
FREQ 2
B1 FILT
B2 FILT
–V
V
B
SCHAEVITZ E 100
MECHANICAL POSITION INPUT
S
C
AD598
SLAVE 2
OS
FEEDBACK
16
13
12
10
15
14
11
OFFSET 2
9
OFFSET 1
OUT FILT
SIG OUT
SIG REF
A1 FILT
A2 FILT
500KHZ
+V
+V
V
S
A
S
2.5k
20
19
18
17
16
15
14
13
12
11
LVDT
AD598
CK
82.5k
+V
FREQ
0.33 F
OUT
0.1 F
+V
S