Who can help me see what is going on with the output of this AD623?

[RachelAnne]

The pressure bridge on my left is a pressure sensor with four pins (1: NC. 2: Vsupply. 3: OUTPUT+. 4: GND). Pin 1 is floating, pin 2 is connected to 5V voltage, and pin 3 is connected to AD623 3 Pin (+In), pin 4 is grounded.
Pin 2 (-In) and pin 4 (-Vs) of my AD623 are grounded, pin 7 (+Vs) is connected to the 5V voltage, pin 5 reaches the 0.4V voltage as shown in the figure, and pins 1 and 8 are connected to a 100 ohm potentiometer. Now the measured voltage of pin 3 is about 0.508V, but the output of pin 6 is always only about 0.023V. Later, when pins 1 and 8 were opened, the gain was changed to 1, but the output was still about 0.02V.

Reference:

AD623 Instrumentation Amplifier: Pinout, Circuit and Alternatives Hello, everybody! I welcome you on board. I am glad to see you around. In this post today, I’ll walk you through the Introduction to AD623. AD623 is a single and dual supply, rail-to-rail, low cost instrumentation amplifier. I suggest you buckle up since I’ll introduce the complete Introduction... www.utmel.com

 

[KlausST]

Hi,

What´s the nominal (unloaded) output voltage of your pressure sensor?
Use a 2 resistor voltage divider to generate this voltage and input it on AD623_pin2.

Datasheet: always use the datasheet directly from the manufacturer. It provides the most rleiable and most up to date informations. Also the manufacturer internet pages to the according part usually give a lot of additional information.
(application notes, example circuits, simulation tools...)

What´s the output range of your pressure sensor?

Klaus

 

[danadakk]

The pressure bridge on my left is a pressure sensor with four pins (1: NC. 2: Vsupply. 3: OUTPUT+. 4: GND). Pin 1 is floating, pin 2 is connected to 5V voltage, and pin 3 is connected to AD623 3 Pin (+In), pin 4 is grounded.
Pin 2 (-In) and pin 4 (-Vs) of my AD623 are grounded, pin 7 (+Vs) is connected to the 5V voltage, pin 5 reaches the 0.4V voltage as shown in the figure, and pins 1 and 8 are connected to a 100 ohm potentiometer. Now the measured voltage of pin 3 is about 0.508V, but the output of pin 6 is always only about 0.023V. Later, when pins 1 and 8 were opened, the gain was changed to 1, but the output was still about 0.02V.

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If I look at your pin connection description versus the diagram the inconsistences stand out.

The diagram is correct.

Here is a tool to determine what voltages should produce what output. Note the AD623 is
not in the tool, post on ADI website a question what IA you could pick in tool that closely
matches AD623, the engineering department will help.


Regards, Dana.

--- Updated Aug 17, 2021 ---

You mention pin 1 is floating on PT, but diagram clearly needs Pwr and Gnd to PT, and the other two
connections to diff amp input. Unless PT is 1/2 bridge.

Also be careful with setting up offset in bridge, the AD623 is NOT R-R on its inputs.



Regards, Dana.

--- Updated Aug 17, 2021 ---

A sim sweeping R2 in bridge from 950 to 1050 ohms.

Regards, Dana.

--- Updated Aug 17, 2021 ---

Sweep done with Rg set to 1K, bridge sweep basically +/- 10 mV