Temperature Sensors Primer

Getting to Know Temperature Sensors This page will detail the various common types of temperature sensors, and their uses, advantages, and disadvantages.

Integrated Temperature Sensors

A TMP1000

In simple terms, integrated temperature sensors sense the temperature of the circuit board. These are useful as an easy way to measure the air temperature wherever the sensor is located.

Pros:

• Simple
• Accurate
• Inexpensive

Cons

• Only effective for measuring ambient (air) temperature
• Must be kept dry
• Narrower temperature range than other sensors (max 85°C)
• Slowest reaction time (the whole circuit board needs to adjust to changes)

Common Uses

Remotely Operated Ambient Temperature Sensor

These are commonly used in weather-sensing and climate-control applications.

1. Weather Stations
2. Thermostat

How to Use with Phidgets

1. Put the sensor in the environment you want to sense the temperature, and you're good to go!
2. Use the TemperatureSensor software object to get the temperature from the sensor

Phidgets that use this kind of sensor include:

• TMP1000 Temperature Phidget
• HUM1000 Humidity Phidget

Integrated temperature sensors are also included in all Thermocouple Phidgets.

A TMP1100 with a thermocouple

Thermocouples

Thermocouples Measuring Temperature in a Smoker, and Food Temperature

Thermocouples use thermoelectric effects to measure the temperature at the end of a thermocouple probe. Thermocouples are often used to measure the temperature in environments that would be too hot or otherwise impractical to place an integrated temperature sensor.

Pros

• Widest measurement range (up to 1260°C for some K-type thermocouples)
• The probe can go almost anywhere
• Bead-type thermocouple has the fastest reaction time of any sensor covered here
• Inexpensive

Cons

• Not as accurate as integrated temperature sensors or RTD

Common Uses

Thermocouples are used in applications too hot for other sensor types, or where the convenience of a temperature probe is important.

1. Oven temperature control
2. Food temperature measurement

How to Use with Phidgets

Thermocouple Wiring

1. Attach the two wires from the thermocouple probe to the Thermocouple Phidget.

A thermocouple probe in a smoker

2. Place the probe where you want to sense temperature.
3. Use the TemperatureSensor object to get the temperature of the probe.

Examples of thermocouple Phidgets include:

• TMP1100 Isolated Thermocouple Phidget
• TMP1101 4x Thermocouple Phidget

RTDs

TMP1200 with an RTD

RTDs (Resistance Temperature Detectors) use the property of metals to change resistance with temperature to calculate the temperature of a probe. They can be used in many of the same applications as thermocouples, and are generally more accurate, though more expensive.

Pros

• Wide measurement range (up to 600°C)
• The probe can go almost anywhere
• Most accurate on this list (given the right RTD probe)

Cons

• More expensive than other options
• Slower than bead-type thermocouple

Common Uses

RTDs are commonly used in applications where the highest accuracy is essential, and are used to monitor and control a variety of industrial systems and processes.

How to Use with Phidgets

RTD Wiring

1. Attach the wires from the RTD probe to the RTD Phidget.

RTD Placed in Ice

2. Place the probe where you want to sense temperature.
3. Use the TemperatureSensor object to get the temperature of the probe.

The RTD Phidget is the TMP1200 RTD Phidget

Infrared Temperature Sensors

Infrared temperature sensors detect the surface temperature of an object in its field of view using infrared light. These are useful for measuring the temperature of things at a distance. These sensors typically take an average temperature of everything in their field of view. For best results, the target must act similarly to a black-body in the infrared spectrum, meaning it absorbs all infrared light, rather than reflecting it or allowing it to pass through.

If the surface is reflective to infrared light, the sensor will not be able to get an accurate reading of the objects surface temperature, instead seeing the reflected light.

Interestingly, glass is opaque to infrared light, meaning that infrared temperature sensors cannot see through it, and will measure the temperature of the glass.

Pros:

• Doesn't need to touch the object being measured

Cons

• Less accurate than other types
• Needs line-of-sight to the object being measured
• Only measures surface temperature

Common Uses

Infrared temperature sensors are good for measuring the temperature of things where it would be impractical to attach a probe, and are mostly used to measure the temperature of moving objects.

• Hand-held temperature sensing
• Car brake temperature testing

How to Use with Phidgets

1. Point the sensor at the object you want to measure the temperature of.
2. Use the TemperatureSensor software object

The IR temperature sensor Phidget is the 1045 PhidgetTemperatureSensor IR

Thermistors

Like RTDs, thermistors are temperature sensing devices that rely on changing resistance to detect temperature. Unlike RTDs, thermistors used in temperature sensing applications are typically made from ceramic materials which decrease in resistance as they are heated up. Also unlike RTDs, they have a non-linear resistance/temperature curve.

Pros:

• Inexpensive
• Fast reaction time
• More accurate than thermocouples

Cons:

• Non-linear behaviour needs to be accounted for
• Not standardized (there are many different thermistors with many different characteristics)
• Narrow temperature range
• (Not directly supported by Phidgets)

Common Uses

Thermistors are commonly used in a wide range of temperature sensing applications:

• Ambient temperature measurement for thermostats
• Fluid temperature measurement in cars

How to Use with Phidgets

1. Attach the wires from the thermistor to the RTD Phidget
2. Place the thermistor where you want to sense temperature
3. Use the ResistanceInput object to measure the resistance of the thermistor
4. Calculate the temperature using data provided on the thermistor's datasheet

Summary

	Typical Range (Max)	Sensing Method	Typical Error	Maximum Error	Speed (Typical)	Cost
Integrated	85°C (TMP1000)	Air	0.25°C	1°C	>5s	$
Thermocouple	1260°C (K-Type)	Probe / Contact	0.75°C	10°C (K-Type at 1260°C)	0.5s - 3s	$
RTD	600°C (Platinum RTD)	Probe / Contact	0.1 °C (Class AA probe at 0°C)	3.5°C (Class B probe at 600°C)	2s - 10s	$$ - $$$
Infrared	380°C (Phidget 1045)	Line-of-Sight	0.5°C	4°C	0.25s - 0.5s	$$ - $$$
Thermistor	125°C - 200°C (Thermistor Dependant)	Probe / Contact / Air	0.2°C	4°C+ (Thermistor Dependant)	0.25s - 0.5s	$