am457 AME, Inc., am457 Datasheet - Page 7

• Manufacturer Part Number: am457
• Description: Precision Amplifier For Bridge Circuits - Analog Microelectronics
• Manufacturer: AME, Inc.

Precision amplifier for bridge circuits
EXAMPLE APPLICATION
Offset and span compensation for a Wheatstone bridge with discrete adjusting resistors.
AM457 is suitable for the amplification of all resistance bridge circuits (four-resistor bridges)
with low sensitivity.
To compensate for or calibrate the offset and span and to amplify the signal as necessary a network
was developed (see Figure 2) for a four-resistor resistance bridge circuit (such as a DMS sensing
element, for example) consisting of the resistance bridge, an AM457 IC, four resistors and a
maximum of six capacitors (see [1]). AM457's characteristics define the network and the IC
amplifies the bridge output signal to the required output values.
The formulae used here to calibrate the offset and span of a bridge circuit are calculated using a
model which is based on the classic Wheatstone bridge circuit of four resistors.
On the basis of this model three simple equations were approximated for the setting of the resistors;
they are also suitable for calibration using a minimum of data pertinent to the sensing element and
without any need for further correction.
analog microelectronics
Analog Microelectronics GmbH
An der Fahrt 13, D – 55124 Mainz
Internet: www.analogmicro.de
Figure 2: Schematic circuit diagram for resistance bridges with low sensitivity
R
R
4
3
C
2
C
R
C
6
1
4
7
2
6
3
AM457
OUTOP
IN+
IN-
INOP
Phone:
Fax:
Email:
AMP
+49 (0)6131/91 073 – 30
+49 (0)6131/91 073 – 0
[e-mail]
OP
Temp
1k
Diagnostic
9k
unit
4
V
GND
CC
DIAG
VCC
OUT
5
8
1
C
C
5
1
AM457
GND
V =5V
V
V
CC
May 2005
OUT
DIAG
Rev. 2.2
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