# Instrumentation Amplifiers

## What is an instrumentation amp?

<figure><img src="/files/uXW7c7sySQDVoyrkOaob" alt=""><figcaption><p>The internal schematic for the <a href="https://punchout.digikey.com/en/products/detail/texas-instruments/INA821IDR/10448327">INA821D</a> instrumentation amplifier</p></figcaption></figure>

## Design considerations

### Setting the gain

Instrumentation amps take in signals and amplify them by a gain value set using a gain resistor put between two of the ports. The instrumentation amplifier manual will include an equation for calculating the resistor value for a chosen gain. Then you just wire the resistor between the two ports.

### Input orientation matters

Instrumentation amps have two inputs, typically marked as IN+ and IN-. Which of your two signals goes into which pin matters, as it sets the polarity of the signal. Using the strain gauge as an example, connecting the inputs one way will result in tension producing positive strain, while flipping them will result in compression producing positive strain.   It's recommended you prototype your circuit that uses an instrumentation amp on a breadboard first to ensure your inputs are oriented correctly.&#x20;


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://wvu-neuromint.gitbook.io/neuromint-resources/technical-guides/circuit-board-components/instrumentation-amplifiers.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.