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).
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:
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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