9.2 Typical Applications

9.2.1 Resistive-Bridge Pressure Sensor

The INA823 is an integrated instrumentation amplifier that measures small differential voltages while

simultaneously rejecting larger common-mode voltages. The device offers a low power consumption of 250

µA (max) and high precision, thus minimizing errors with voltage offset, offset drift and gain error.

The device is designed for portable applications where sensors measure physical parameters, such as changes

in fluid, pressure, temperature, or humidity. An example of a pressure sensor used in the medical sector is in

portable infusion pumps or dialysis machines.

The pressure sensor is made of a piezo-resistive element that can be derived as a classical 4-resistor

Wheatstone bridge.

Occlusion (infusion of fluids, medication, or nutrients) happens only in one direction, and therefore can only

cause the resistive element (R) to expand. This expansion causes a change in voltage on one leg of the

Figure 9-2 showcases an exemplary circuit for an occlusion pressure sensor application, as required in infusion

pumps. When blockage (occlusion) occurs against a set-point value, the tubing depresses, thus causing the

piezo-resistive element to expand (Node AD: R + ΔR). The signal chain connected to the bridge downstream

processes the pressure change and can trigger an alarm.

GND

+

–

RG

INA823

VREF

0.1 F

ADC

Pressure

occlusion

sensor

µC

A

B

C

D

REF5050

1 F

1 F

R9

R8

Figure 9-2. Resistive-Bridge Pressure Sensor

Low-tolerance bridge resistors must be used to minimize the offset and gain errors.

Given that there is only a positive differential voltage applied, this circuit is laid out in single-ended supply

introduced.

The REF5050 is a low-noise, low-drift (3 ppm/C), and high-precision (0.05%) voltage reference that is an

The following subsections give the design requirements and detailed design procedure for an application with a

occlusion pressure sensor.

For more information and design tips to consider when using a resistive-bride pressure sensor, see the Design

tips for a resistive-bridge pressure sensor in industrial process-control systems analog applications journal.

www.ti.com

INA823

SBOSA75A – JULY 2021 – REVISED JULY 2021

Copyright © 2021 Texas Instruments Incorporated

Submit Document Feedback

19

Product Folder Links: INA823