Part No : AD698 circuitFile Size : 29 KB Pages : 12 Pages - AD698 Pinout
- 1. LVDTs connected in the series opposed configuration. Both ex- Application Circuit
- 2. To use an LVDT in a closed-loop mechanical servo application, Application Schematic
- 3. 20. AD698 Interconnection Diagram for AC Bridge Applications Typical Circuit
## Other Part Numbers in this pdf fileAD698SQ AD698APZ AD698AP | find AD698 datasheet |

CONNECTING THE **AD698**

The **AD698** can easily be connected for dual or Single Supply

operation as shown in Figures 7, 8 and 13. The following gen-

eral design procedures demonstrate how external component

values are selected and can be used for any LVDT that meets

channels and the A channel Comparators will depend on which

transducer is used. In general follow the guidelines below.

Parameters set with external passive components include: exci-

tation frequency and amplitude, **AD698** input signal frequency,

and the scale factor (V/inch). Additionally, there are optional

features; offset null adjustment, filtering, and signal integration,

which can be implemented by adding external components.

+15V

–15V

6.8µF

100nF

1 –V

S

2 EXC1

3 EXC2

4 LEV1

R1

5 LEV2

C1

15nF

SIG OUT 20

R2

33kΩ

C4

7 FREQ2

8 BFILT1

C2

9 BFILT2

10 –BIN

11 +BIN

12 –AIN

AFILT2 16

–ACOMP 15

+ACOMP 14

+AIN 13

OUT FILT 18

AFILT1 17

C3

1000pF

V

OUT

6.8µF

100nF

3. Select a suitable LVDT that will operate with an excitation

frequency of 2.5 kHz. The Schaevitz E100 for instance, will

operate over a range of 50 Hz to 10 kHz and is an eligible

candidate for this example.

4. Select excitation frequency determining component C1.

C1

=

35

µF

Hz/f

EXCITATION

+15V

–15V

6.8µF

100nF

1 –V

S

2 EXC1

3 EXC2

4 LEV1

R1

5 LEV2

SIG OUT 20

R2

6.8µF

100nF

+V

S

24

R4

R3

OFFSET1 23

OFFSET2 22

SIG REF 21

R

L

V

OUT

SIGNAL

REFERENCE

+V

S

24

R4

R3

C1

6 FREQ1 FEEDBACK 19

C4 1000pF

7 FREQ2

OUT FILT 18

AFILT1 17

C3

9 BFILT2

10 –BIN

11 +BIN

12 –AIN

AFILT2 16

–ACOMP 15

+ACOMP 14

A

+AIN 13

PHASE

LAG/LEAD

NETWORK

C

D

B

OFFSET1 23

OFFSET2 22

SIG REF 21

R

L

SIGNAL

REFERENCE

8 BFILT1

C2

6 FREQ1 FEEDBACK 19

1M

PHASE LAG

A

B

C

R

T

C

D

PHASE LEAD

A

B

R

T

R

S

C

D

PHASE LAG = Arc Tan (Hz RC);

PHASE LEAD = Arc Tan 1/(Hz RC)

WHERE R = R

S

// (R

S

+ R

T

)

R

S

R

S

C

C

Figure 7. Interconnection Diagram for Half-Bridge LVDT

and Dual Supply Operation

DESIGN PROCEDURE

DUAL SUPPLY OPERATION

Figure 8. **AD698** Interconnection Diagram for Series

Opposed LVDT and Dual Supply Operation

B. Determine the Oscillator Amplitude

Figure 7 shows the connection method for half-bridge LVDTs.

Figure 8 demonstrates the connections for 3- and 4-WIRE

LVDTs connected in the series opposed configuration. Both ex-

amples use dual

±

15 volt power supplies.

A. Determine the Oscillator Frequency

Frequency is often determined by the required BW of the sys-

tem. However, in some systems the frequency is set to match

the LVDT zero phase frequency as recommended by the

manufacturer; in this case skip to Step 4.

1. Determine the mechanical bandwidth required for LVDT

position measurement subsystem, f

SUBSYSTEM

. For this ex-

ample, assume f

SUBSYSTEM

= 250 Hz.

2. Select minimum LVDT excitation frequency approximately

10

×

f

SUBSYSTEM

. Therefore, let excitation frequency = 2.5 kHz.

Amplitude is set such that the primary signal is in the 1.0 V to

3.5 V rms range and the secondary signal is in the 0.25 V to

3.5 V rms range when the LVDT is at its mechanical full-scale

position. This optimizes linearity and minimizes noise suscepti-

bility. Since the part is ratiometric, the exact value of the excita-

tion is relatively unimportant.

5. Determine optimum LVDT excitation voltage, V

EXC

. For a

4-WIRE LVDT determine the voltage transformation ratio,

VTR, of the LVDT at its mechanical full scale. VTR =

LVDT sensitivity

×

Maximum Stroke Length from null.

LVDT sensitivity is listed in the LVDT manufacturer’s cata-

log and has units of volts output per volts input per inch dis-

placement. The E100 has a sensitivity of 2.4 mV/V/mil. In

the event that LVDT sensitivity is not given by the manufac-

turer, it can be computed. See section on determining LVDT

sensitivity.

–6–

REV. B