Temperature Reaction Time

Introduction

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

Please note that T100 (or 100% of the final desired temperature) will never be reached because of the laws of physics.

Environment

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

Water will have a much faster response time and the faster the circulation, the faster the response time.

Overview of Simple Hardware devices

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