Measuring Temperature

Covers various ways to measure temperature (e.g., thermocouples, RTD's, thermistors, etc)

Which temperature sensor do I use?

So you want to sense temperature. There are several things to consider as you decide between the various options. For most (room temperature +/- 50 degrees) applications, you could use any of the options below. So how do you decide?! Read on. 

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Claire's quick start guide:

For temperatures above 1000°C : use a thermocouple (Type K, or check other types for their temp range)

Easiest to put on a breadboard (least wiring, doesn't require considering fancy concepts like "cold junction compensation"): TMP36GZ

Fast response time and cheap (maybe you need 100 of them): Thermistor

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Claire's more complete table:

Method How it works Electrical requirements DAQ requirements Temp range Accuracy

TMP36GZ

 

As temp increases, voltage across diode's base and emitter (V_be) decreases at a known rate. This voltage is amplified, and voila.

 

To convert the voltage to temperature, simply use the basic formula:

Temp in °C = [(Vout in mV) - 500] / 10

Requires a current

 

1- 2.7 - 5.5 VCC  (0.05 mA current draw)

2 - analog V_out

3- GND

 

(1-2-3 left to right, part number facing you)

 Analog voltage input up to 2 V 

-40 - 150 °C

 

(-40 - 302 °F)

+/- 0.2°C;

 
Thermocouple Two different metals form a junction (where we sense temperature), and when a change in temperature occurs, a voltage is generated via the Seebeck effect. This voltage is measured by the DAQ and interpreted to give a temperature. Self powered Analog voltage input

(typical, depends on type [K, J, T etc]);

200 - 1750°C 

(typical)

0.5 - 5 °C;

 

0.10 - 10 sec
Thermistor Semiconductor typically combined with binders and stabilizers with a negative or positive temperature coefficient. Basically, temperature increases, and resistance of sensing element increases (PTC) or decreases (NTC) Requires a current Analog voltage input

(typical)

-100 - 325°C

as low as +/- 0.05 °C;

 

0.12 - 10 seconds
RTD (resistance temperature detector) Resistance of a sensing element (usually a pure metal like platinum protected in a sheath/embedded in ceramic) increases as temperature increases Requires a current Analog voltage input

(typical)

-200 - 650 °C

+/- 0.1 to 1 °C;

 

1 - 50 sec

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TMP36GZ (image from Adafruit)

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RTD vs thermistor (nice guide from Omega)

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RTD vs Thermocouple (nice guide from McMaster)

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RTD vs thermistor

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Comparing thermocouple types

This is a nice link: link

Type T thermocouples (Cu/constantan or blue/red) have an accuracy of $/pm$ 1 degree C, whereas Type K thermocouples have an accuracy of $/pm$ 2.2C.