AD598 Analog Devices, AD598 Datasheet - Page 7

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

8. C2, C3 and C4 are a function of the desired bandwidth of
9. In order to Compute R2, which sets the AD598 gain or full-
10. Selections of R3 and R4 permit a positive or negative output
REV. A
the AD598 position measurement subsystem. They should
be nominally equal values.
If the desired system bandwidth is 250 Hz, then
See Figures 13, 14 and 15 for more information about
AD598 bandwidth and phase characterization.
scale output range, several pieces of information are needed:
a. LVDT sensitivity, S
b. Full-scale core displacement, d
c. Ratio of manufacturer recommended primary drive level,
LVDT sensitivity is listed in the LVDT manufacturer’s cata-
log and has units of millivolts output per volts input per inch
displacement. The E100 has a sensitivity of 2.4 mV/V/mil.
In the event that LVDT sensitivity is not given by the manu-
facturer, it can be computed. See section on Determining
LVDT Sensitivity.
For a full-scale displacement of d inches, voltage out of the
AD598 is computed as
V
Pin 17 shown in Figure 7.
Solving for R2,
Note that V
determine (V
For V
full-scale displacement ( 0.1 inch),
V
shown in Figure 9.
voltage offset adjustment.
*These values have a 20% tolerance.
OUT
OUT
V
PRI
V
OUT
C2 = C3 = C4 = 10
is measured with respect to the signal reference,
as a function of displacement for the above example is
OS
C2 = C3 = C4 = 10
to (V
V
Figure 9. V
vs. Core Displacement ( 0.1 Inch)
R2
OUT
= 20 V full-scale range ( 10 V) and d = 0.2 inch
1.2V
R2
PRI
A
–
A
+ V
2.4 3 500 A 0.2
0.1
+ V
is the same signal level used in Step 4 to
S
B
S V
20V
V
B
) computed in Step 4.
+ 10
–
OUT
OUT
R2
V
).
10
OUT
(V
(
VOLTS)
PRI
A
( 10 V Full Scale)
V
–4
PRI
2.70V
–4
R3 5 k *
V
Farad Hz/250 Hz = 0.4 F
(V
Farad Hz/f
B
500 A d
+ 0.1 d
A
)
1
V
500 A R2 d.
(INCHES)
B
)
SUBSYSTEM
–
75. 3 k
R4 5 k *
1
(Hz)
(1)
(2)
–7–
DESIGN PROCEDURE
SINGLE SUPPLY OPERATION
Figure 12 shows the single supply connection method.
For single supply operation, repeat Steps 1 through 10 of the
design procedure for dual supply operation, then complete the
additional Steps 11 through 14 below. R5, R6 and C5 are addi-
tional component values to be determined. V
with respect to SIGNAL REFERENCE.
11. Compute a maximum value of R5 and R6 based upon the
12. The voltage drop across R5 must be greater than
R5
For no offset adjustment R3 and R4 should be open circuit.
To design a circuit producing a 0 V to +10 V output for a
displacement of 0.1 inch, set V
and solve Equation (1) for R2.
This will produce a response shown in Figure 10.
In Equation (2) set V
Since a positive offset is desired, let R4 be open circuit.
Rearranging Equation (2) and solving for R3
Figure 11 shows the desired response.
relationship
Therefore
*These values have 20% tolerance.
Based upon the constraints of R5 + R6 (Step 11) and R5
(Step 12), select an interim value of R6.
2 10 k *
2 10 k *
Figure 10. V
vs. Core Displacement ( 0.1 Inch)
Figure 11. V
vs. Displacement ( 0.1 Inch)
R3
–
–
R4 5 k
0.1
R4 5 k
0.1
R5 + R6
1.2V
1.2 R2
1.2 V
V
V
+ 5
OUT
+ 10
OUT
+ 5
–
V
100 A
5
OUT
OUT
OS
OS
R2 = 37.6 k
(
(
VOLTS)
VOLTS)
= 5 V and solve for R3 and R4.
( 5 V Full Scale)
(0 V–10 V Full Scale)
– 5 k
V
250 A
+ 0.1 d
+ 0.1 d
250 A
PS
/100 A
OUT
(INCHES)
(INCHES)
4.02 k
to +10 V, d = 0.2 inch
4 R2
V
4 R2
V
OUT
OUT
OUT
is measured
AD598
Ohms
Volts