This document discusses some of the challenges in obtaining accurate readings from sensors in the physical world. It notes that temperature, humidity, water level, air speed, distance, and vibration sensors can all be affected by factors like thermal mass, placement, ambient conditions, and sensor drift over time. To get useful data from sensors in IoT applications, it is important to understand these real-world challenges and how the environment and placement of sensors can impact readings.

1. In IoT, sensors are used to Digitize the
Physical World to bring that information
into the Cyber World
Some users assume the Digital
Readings are Accurate !. There is a need
to understand this Physical World
challenges

2. Temperature
Thermal Mass of the Temperature Probe limits its
application and can cause in accurate readings
Cannot be used as the
Thermal Mass of IC << that
of the probe
Can be used as
Thermal Mass of Kettle
>> that of the probe
Thermal
Mass Ratio
1: 10 is a
minimum
Temperature

3. T oC
Temperature
Infra Red
Temperature
Two Temperature sensor measuring same Hot object can
give two different temperature readings
Infra red Temperature sensor is an averaged
measurement from a Radiated surface area
Temperature probe is a localised
Conductive measurement

4. Temperature
Temperature probe
Aircon draws warn air from top,
passing through temperature
sensor. The heat exchanger
cools the air ,and then exhaust
cool air into the room
Unless you place the
sensor where you stand !
The temperature is
controlled at that air
inlet point, but NOT at
where you are standing

5. Humidity sensor
Humidity
Readings are affected by Temperature &
Air flow
Placement Height
Wet surrounding affects readings
Humidity

6. Water Level
Hydrostatic Water sensor affected by
ambient air pressure
Sensor is a flexible membrane to
measure water back pressure
This membrane stiffness is affected by
barnacles
Water Level

7. 7
y = mx + c
WaterLevel
Voltage
Converts V to
Water Level
Ideal Laboratory Condition Actual Usage
WaterLevel
Voltage
Measurement
Uncertainty
WaterLevel
Voltage
Sensor Drift
Calibration
curve shift
over time
Outdoor Water Level Sensor accuracy challenges Water Level

8. Air Speed
Anemometer
(Wind Speed) Affected by Placement Location & Height
Need to know sensor placement
High
Rise
Building
Top ViewSide View

9. Ultra-Sonic Sensor
Distance
Affected by Size and Shape of Object (US waves reflects
back) and Humidity (Air density)

10. LIDAR Photonics
Distance
Affected by Surface texture, Reflectiveness of Object. Laser
goes through glass

11. Vibration
Vibration
3 Axis X Y Z
Mass can affect readings
Placement is key
Need to know why place
sensor there