REV. B

–8–

AD698

value .

Figure 12 shows the desired response.

+5

+0.1d (INCHES)

–0.1

V

OUT

(VOLTS)

+10

(

±0.1 Inch)

DESIGN PROCEDURE

SINGLE SUPPLY OPERATION

Figure 13 shows the single supply connection method.

R1

C1

C2

C3

R4

R3

13

16

15

14

24

23

22

21

20

19

18

17

12

11

10

9

8

1

2

3

4

7

6

5

AD698

EXC1

EXC2

LEV1

LEV2

FREQ1

BFILT1

BFILT2

–BIN

+BIN

–AIN

FREQ2

SIG REF

OFFSET2

OFFSET1

OUT FILT

FEEDBACK

SIG OUT

–ACOMP

AFILT2

AFILT1

+ACOMP

+AIN

C4

R2

1000pF

SIGNAL

REFERENCE

0.1µF

+30V

6.8µF

1M

R6

R5

C5

AB

C

D

PHASE

LAG/LEAD

NETWORK

AB

CD

PHASE LEAD

C

C

A

B

CD

PHASE LAG

C

PHASE LAG = Arc Tan (Hz RC);

PHASE LEAD = Arc Tan 1/(Hz RC)

Figure 13. Interconnection Diagram for Single Supply

Operation

For single supply operation, repeat Steps 1 through 10 of the

design procedure for dual supply operation. R5, R6 and C5 are

sured with respect to SIGNAL REFERENCE.

10. Compute a maximum value of R5 and R6 based upon the

relationship

R5 + R6

≤ V

µA

11. The voltage drop across R5 must be greater than

2

+ 10 kΩ

1.2V

R4

+ 2 kΩ

+ 250 µA +

4

× R2







 Volts

Therefore

R5

≥

2

+ 10 kΩ

1.2V

R4

+ 2 kΩ +

250

µA +

4

× R2









100

µA

Ohms

Based upon the constraints of R5 + R6 (Step 10) and R5 (Step

11), select an interim value of R6.

tions, make sure the voltage drop across R5 is met as de-

fined in Step 11.

As a final check on the power supply voltages, verify that

13. C5 is a bypass capacitor in the range of 0.1

µF to 1 µF.

Gain Phase Characteristics

To use an LVDT in a closed-loop mechanical servo application,

it is necessary to know the dynamic characteristics of the trans-

ducer and interface elements. The transducer itself is very quick

to respond once the core is moved. The dynamics arise prima-

rily from the interface electronics. Figures 14, 15 and 16 show

the frequency response of the AD698 LVDT Signal Conditioner.

Note that Figures 15 and 16 are basically the same; the differ-

ence is frequency range covered. Figure 15 shows a wider range

of mechanical input frequencies at the expense of accuracy.

FREQUENCY – Hz

0

10k

100

1k

10

0

–30

–60

–70

0

–10

–20

–50

–40

–360

–60

–240

–300

–420

–180

–120

0.1µF

0.33µF

2.0µF

R2 = 81k

Ω

0.1µF

0.33µF

2.0µF

R2 = 81k

Ω

Figure 14. Gain and Phase Characteristics vs. Frequency

(0 kHz–10 kHz)