# Temperature Reaction Time

### Introduction <a href="#introduction" id="introduction"></a>

Several measuring points are generally used when determining the response time. Each of them is a time period in seconds required for the sensor reading/output to reach x% of the total value change (difference in temperature).

A single time period is known as **sensor response time** (or thermal response time).

| Percentage | Also used as | Specific term                          |
| ---------- | ------------ | -------------------------------------- |
| 50%        | T50 or t0.5  | *none*                                 |
| 63.2%      | T63 or t0.63 | Sensor Time Constant (τau)             |
| 90%        | T90 or t0.9  | *none*                                 |
| 99.3%      | T99 or t0.99 | 5 times the Sensor Time Constant (τau) |

**EXAMPLE:** For a temperature sensor taken out of an ice bath at 0 °C into a room at 10 °C, it will take exactly: -T50 to reach 5°C -T63.2 (Sensor Time Constant) to reach 6.32 °C -T90 to reach 9°C -T99.3 to reach 9.93°C

{% hint style="danger" %}
Please note that T100 (or 100% of the final desired temperature) **will never be reached** because of the laws of physics.
{% endhint %}

### Environment <a href="#environment" id="environment"></a>

All the reference data must be also related to the **medium** used for the test - you need to keep heat transfer and circulation in mind.

Most commonly found mediums:

* Water with circulation of 0.2 or 0.4 m/s
* Air with circulation of 1 or 2m/s
* And others, any medium needed can be used for the test

{% hint style="success" %}
Water will have a much faster response time and the faster the circulation, the faster the response time.
{% endhint %}

### Overview of Simple Hardware devices <a href="#overview-of-simple-hardware-devices" id="overview-of-simple-hardware-devices"></a>

We are using 4 types of devices:

| Device                 | SimplePack Temp            | SimpleMeter                  | SimpleIndustry (internal probe) | SimpleIndustry (NTC on case) | SimpleIndustry (NTC on cable) |
| ---------------------- | -------------------------- | ---------------------------- | ------------------------------- | ---------------------------- | ----------------------------- |
| **Sensor**             | MEMS                       | MEMS                         | MEMS                            | NTC                          | NTC                           |
| **Placement**          | Inside enclosed case       | Inside case with air intakes | Inside enclosed case            | On the case                  | On the pipe                   |
| **T63 (sensor only)**  | 15s at 1m/s airflow        | 15s at 1m/s airflow          | 15s at 1m/s airflow             | 4s                           | 15s in water                  |
| **T50 (whole device)** | 2min (water), 4min (air)   | 1min (air)                   | 8min (air)                      | 2s                           | 12s in water                  |
| **T63 (whole device)** | 3min (water), 5min (air)   | 1.25min (air)                | 10min (air)                     | 4s                           | 15s in water                  |
| **T90 (whole device)** | 12min (water), 20min (air) | 5min (air)                   | 40min (air)                     | 20s                          | 1min in water                 |


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