AD598

REV. A

–14–

PRECISION DIFFERENTIAL GAGING

The circuit shown in Figure 26 is functionally similar to the dif-

ferential gaging circuit shown in Figure 25. In contrast to Figure

25, it provides a means of independently adjusting the scale fac-

tor of each LVDT so that both scale factors may be matched.

The two LVDTs are driven in a master-slave arrangement

where the output signal from the slave LVDT is summed with

the output signal from the master LVDT. The scale factor of the

slave LVDT only is adjusted with R1 and R2. The summed

scale factor of the master LVDT and the slave LVDT is ad-

justed with R3.

R1 and R2 are chosen to be 80.9 k

Ω resistors to give a ±10 V

full-scale output signal for a single Schaevitz E100 LVDT. R3 is

chosen to be 40.2 k

Ω to give a ±10 V output signal when the

two E100 LVDT output signals are summed. The output volt-

age for this circuit is given by:

+

×

R2

R1









× 500 µA × R3.

EXC 1

EXC 2

LEV 1

LEV 2

FREQ 1

FREQ 2

B1 FILT

B2 FILT

OFFSET 1

OFFSET 2

SIG REF

SIG OUT

FEEDBACK

OUT FILT

A1 FILT

A2 FILT

AD598

1

2

3

4

5

6

7

8

9

10

11

12

13

14

16

15

17

18

19

20

V

B

V

A

0.1

µF

0.33

µF

0.1

µF

–V

0.1

µF

0.1

µF

+V

A

B

C

D

SCHAEVITZ E 100

EXC 1

EXC 2

LEV 1

LEV 2

FREQ 1

FREQ 2

B1 FILT

B2 FILT

OFFSET 1

OFFSET 2

SIG REF

SIG OUT

FEEDBACK

OUT FILT

A1 FILT

A2 FILT

AD598

1

2

3

4

5

6

7

8

9

10

11

12

13

14

16

15

17

18

19

20

0.015

µF

0.1

µF

0.33

µF

0.1

µF

–V

0.1

µF

0.1

µF

+V

R3

40.2k

Ω

SLAVE

LVDT

MASTER LVDT

15k

Ω

15k

Ω

R2

80.9k

Ω

R1

80.9k

Ω

A

+

•

•

R2

R1

500

± 10V

FULL SCALE

Figure 26. Precision Differential Gaging