9

LT1031/LH0070

1031fb

Strain Gauge Conditioner

for 350

Ω Bridge

Ultralinear Platinum Temperature Sensor*

APPLICATIO CIRCUITS

–

+

LT1031

GND

OUT

IN

20V

20V

–15V

–15V

2

3

7

4

6

–50

°C ≤ T ≤ 150°C

R2*

5k

R14

5k

R12

1k

R15

10k

R13

24.3k

R10

182k

1%

R11

6.65M

1%

R5

200k

1%

R6

619k

1%

R4

4.75k

1%

R7

392k

1%

†

100

Ω

AT 0

°C

R1**

253k

R8

10M

R9

100k

R3**

5k

654k

STANDARD INDUSTRIAL 100

Ω PLATINUM 4-WIRE SENSOR, ROSEMOUNT 78S,

OR EQUIVALENT.

α = 0.00385

USE TRIM SEQUENCE AS SHOWN. TRIMS ARE NON-INTERACTIVE SO THAT ONLY ONE

TRIM SEQUENCE IS NORMALLY REQUIRED.

FEEDBACK LINEARIZES OUTPUT TO

±0.005°C FROM – 50°C TO 150°C

WIREWOUND RESISTORS WITH LOW TC

†

*

**

LT1031 • AC06

LT1001

R2

20k

R4

20k

R1

357

Ω

1/2W

357

Ω

1/2W

R6

2M

Ω*

R3

2M

Ω

R5

2M

350

Ω STRAIN

GUAGE BRIDGE**

LT1031 • AC05

5V

–5V

100pF

6

6

8

1

3

3

2

2

28mA

28.5mA

15V

–15V

LT1031

LT1012C

LM301A

†

GND

IN

OUT

–

+

THIS RESISTOR PROVIDES POSITIVE FEEDBACK TO THE BRIDGE TO ELIMINATE

≥ 1MΩ. IF R2–R5 ARE CHANGED, SET R6 = R3

BRIDGE IS ULTRA LINEAR WHEN ALL LEGS ARE ACTIVE, TWO IN COMPRESSION

AND TWO IN TENSION, OR WHEN ONE SIDE IS ACTIVE WITH ONE COMPRESSED

AND ONE TENSIONED LEG

OFFSET AND DRIFT OF LM301A ARE VIRTUALLY ELIMINATED BY DIFERENTIAL

CONNECTION OF LT1012C

*

**

†