Temperature & humidity sensors

The 3 most popular Temperature & humidity sensors

What is a sensor?

A sensor can be considered an artificial sense organ in technology. With a sensor, a system perceives its environment or collects information that can be used to control actions. Most sensors are either electronic or mechanical, providing a fixed output based on a certain input.

What can you measure with a sensor?

Naturally, different sensors exist for various applications. Here's a brief list of quantities you can measure with sensors:

• Radiation
• Temperature
• Gases (such as humidity or CO2)
• Pressure
• Magnetism
• Level (such as water level in a tank)
• Movement
• Proximity
• Light/UV/infrared/colors
• Sound
• Distance
• Weight/force
• Orientation/direction
• Current

What should I look for when choosing a sensor?

Voltage

When choosing a sensor, it's important to know the voltage at which the sensor operates. Too high voltage will destroy the sensor, and too low voltage will make it work improperly or not at all. Mechanical sensors are less affected by this.

Output Type

All sensors have one or multiple outputs. An output sends a measurement value from a sensor. The nature of this signal depends on the type of the sensor's output.

• Digital output: A sensor with a digital output signals a logical value of 0 or 1. This means the signal is either present '1' or not '0'. There are thus two states. A digital output is very suitable for detecting the presence or absence of an object or for determining if a certain preset limit has been reached. Additionally, a digital signal can also convey numbers or entire registers through a defined communication protocol like I2C or SPI.
• Analog output: A sensor with an analog output provides a specific analog value (current, voltage, or resistance) based on the recorded input. For example, in measuring temperature, the output could display the value 27°C but also 50°C or 100°C. The advantage of analog output is that it can be directly connected to an actuator, like a sound sensor to an LED (VU meter). There are also ADC (analog to digital) converters available to make the analog signal digital.
• PNP Or NPN: Sensors with a PNP or NPN switching output have at least three connecting wires. The ‘+’ is the brown wire (pin 1), ‘-‘ is the blue wire (pin 3), and the switching wire is the black wire (pin 4). With a PNP switching output, the load is switched between the switching wire and the '-'. With an NPN switching output, the load is switched between the switching wire and the '+'.
• PushPull-switching output: This output is used when both NPN and PNP are required. A voltage above a certain value will cause NPN to switch, while a lower value will cause PNP to switch.
• Normally open/ normally closed: Furthermore, an output can be normally open (NO) or normally closed (NC). In a normally open output, the sensor will provide a '0' signal before switching and a '1' signal after switching. In a normally closed contact, this is reversed: a '1' signal before switching and a '0' signal after switching.

Measuring Range

It's important to know that a sensor has a certain measuring range. This range is clearly indicated for each sensor. If there's a range from 5mm – 250mm, the sensor can only measure within these distances. Any distance outside this range will either produce no output or an undefined one. These distances vary from sensor to sensor.

Resolution

By resolution, we mean "the smallest possible change a sensor can detect." For a positioning laser, this would be a shift or deviation in position. Often, higher resolution is associated with a more expensive sensor and/or slower reading time, so don't immediately opt for the highest available resolution.

How reliable is a sensor?

Generally, sensors are very reliable if you stay within their specifications. It's crucial to choose the right sensor for the application and consider its properties. A low-resolution sensor, for instance, will not be reliable for positioning objects on a PCB but will be reliable enough for less precise work, like avoiding obstacles with a robot.

How do you maintain a sensor?

Maintenance varies by sensor type. Mechanical sensors often require more maintenance than electronic sensors. Sometimes it's necessary to clean the sensor or replace components like lenses or filters. For sensors used in an industrial setting, regular inspection and calibration are recommended to ensure reliable operation.

How can I calibrate a sensor?

Calibration is crucial to ensure the accuracy of a sensor. The process depends on the type of sensor but generally involves comparing the sensor's output with a known standard value. Based on this comparison, adjustments are made as needed. Many sensors have built-in calibration procedures, but some require external equipment.