03. Temperature Sensors

NOTE: INC

1600

When was thermometer (water expansion, mercury) discovered?

1650

The year when first attempts were conducted at temperature scales.

1700

Advent of “standard” temperature scales (Magelotti, Renaldini, Newton) - did not catch

1708

The year when Fahrenheit scale was invented (180 div.)

1742

This is when Celsius scale was discovered.

1848

The discovery of Kelvin scale, which is based on Carnot’s thermodynamic work.

Carnot’s thermodynamic work

Whose work is the Kelvin scale based on?

1927

IPTS was founded.

International Practical Temperature Scale

What does IPTS stand for?

TRUE

(TRUE or FALSE) Temperature sensors are the oldest.

1821

Seebeck effect’s year of discovery.

Thomas Johann Seebeck

Who discovered the Seebeck effect?

1826

When was the first sensor, which is a thermocouple, was discovered?

Antoine Cesar Becquerel

Who discovered the first sensor (thermocouple)?

Seebeck effect

The first sensor is based on what concept?

1834

When was the Peltier effect discovered by Charles Athanese Peltier?

Charles Athanese Peltier

Who discovered the Peltier effect?

1960s

The first Peltier cell is built in what year?

Peltier cell

This is a cell used for cooling and heating.

1821

This is when temperature dependence of conductivity was discovered by Sir Humphrey Davey.

Sir Humphrey Davey

Who discovered the temperature dependence of conductivity?

1771

This is the year when the first resistive sensor made of platinum was built by William Siemens.

William Siemens

Who built the first resistive sensor in 1771?

platinum

From what material is the first resistive sensor was built?

TRUE

(TRUE or FALSE) Temperature sensors are deceptively simple.

thermocouples

These are any two dissimilar materials, welded together at one end and connected to a micro-voltmeter.

micro-voltmeter

Which device are thermocouples connected?

Peltier cell

Any thermocouple connected to a dc source.

dc source

Which source is Peltier cell connected?

resistive sensor

It is a length of a conductor connected to an ohmmeter.

resistive sensor

Which device are ohmmeters connected?

TRUE

(TRUE or FALSE) Some temperature sensors can act as actuators as well.

TRUE

(TRUE or FALSE) Temperature sensors can be used to measure other quantities (electromagnetic radiation, air speed, flow, etc.)

TRUE

(TRUE or FALSE) Some newer sensors are semiconductor-based.

* thermoelectric sensors
* thermoresistive sensors and actuators
* semiconductor junction sensors

What are the types of temperature sensors?

thermoelectric sensor

It is a type of temperature sensor, which is comprised of thermocouples, thermopiles, and Peltier cells.

Peltier cell

It is a thermoelectric sensor that can be used both as actuators and sensors.

thermoresistive sensor and actuator

It is a type of temperature sensor, which are comprised of conductor-based sensors and actuators (RTDs) and semiconductor-based sensors - thermistor, diodes.

* Based on secondary effects (speed of sound, phase of light)
* Indirect sensing (infrared thermometers)
* expansion of metals, bimetals

Other types of temperature sensors?

thermal actuators

* Bimetal actuators
* Expansion actuators
* Thermal displays
* Sometimes sensing and actuation is combined in a single device.

RTDs and thermistorss

What are the two basic types of thermoresistive sensors?

Resistance Temperature Detective

What does RTD stand for?

metal wire, thin film, and silicon-based

Examples of RTDs (HINT: MTS)

thermal resistors

What is the other term for thermistors?

NTC and PTC

What are the two types of thermistors/thermal resistors?

Negative Temperature Coefficient

What does NTC stand for?

Positive Temperature Coefficient

What does PTC stand for?

NTC (Negative Temperature Coefficient)

The higher the temperature, the lower the resistance.

PTC (Positive Temperature Coefficient)

The higher the temperature, the higher the resistance.

5\.7-5.9x10^7 S/m

What is the conductivity \[S/m\] of Copper (Cu)

0\.0039

What is the temperature coefficient resistance (TCR) C^-1 of Copper (Cu)

TRUE

(TRUE or FALSE) Tension or strain on the wires affect resistance.

TRUE

(TRUE or FALSE) Tensioning a conductor, changes its length and cross-sectional area (constant volume).

TRUE

(TRUE or FALSE) Tension or strain has exactly the same effect on resistance as a change in temperature.

TRUE

(TRUE or FALSE) Increase in strain on the conductor increases the resistance of the conductor.

strain gauge

Increasing the strain on the conductor increases the resistance of the conductor.

TRUE

(TRUE or FALSE) Resistance should be relatively large (25Ω and up)

A spool ofnwire (length)

* Similar to heating elements
* Uniform wire
* Chemically and dimensionally stable in the sensing range
* Made thin (

TRUE

(TRUE or FALSE) Spool is supported by a glass (pyrex) or mica support.

glass (pyrex) or mica support

It keeps strain at a minimum and allows thermal expansion.

TRUE

(TRUE or FALSE) Smaller sensors may not have an internal support

RTDs (Resistance Temperature Detector)

It is enclosed in a glass, ceramic or metal enclosure.

TRUE

(TRUE or FALSE) In the enclosure of RTD, its length is from a few cm, to about 50cm.

Platinum

It is used for precision applications. It is also chemically stable at high temperatures.

\-250°-800°C

Platinum is useful to about how many temperature range?

Nickel and Copper

They are less expensive and have a reduced temperature range. At higher temperatures, evaporation increases resistance.

300°C

Copper only works at what temperature?

Thin film sensors

They are produced by produced by depositing a thin layer of a suitable material (platinum or its alloys) on a thermally stable, electrically conducting ceramic.

Thin film sensors

They are small and relatively inexpensive. They are etched to form a long strip (in a meander fashion). The choice in modern sensors.

\-250°C-700°C

Temperature range of thin film RTDs

RTDs (Resistance Temperature Detectors)

They are subject to errors due to rise in their temperature produced by the heat generated in them by the current used to measure their resistance.

Pd = I^2R (I=current (RMS) and R=resistance)

Power dissipated in RTDs

temperature rise per unit power (°C/mW) or power needed to raise temperature (mW/°C)

RTDs are given as what?

0\.01°C/mW-10°C/mW

In RTDs errors are of the order of what range?

silicon resistive sensors

Conduction in semiconductors

Valence electrons

They are bound to atoms in outer layers (most electrons in pure semiconductors).

valence electrons

They can be removed through heat (band gap energy).

valence electrons

When they are removed, they become conducting electrons (conduction band)

NTC

Resistance decreases with temperature (pure silicon)

doping

To increase carrier density, this must be done to semiconductors.

Arsenic (As) and Antimony (Sb)

What should be added to an n-type silicon for doping purposes?

PTC

Resistance increases with temperature.

TRUE

(TRUE or FALSE) PTC of silicon resistive sensors is up to about 200°C.

TRUE

TRUE or FALSE: Silicon resistive sensors are s0mewhat nonlinear and offer sensitivities of the order 0.5-0.7%/°C.

silicon resistive sensors

They are made as a small chip with 2 electrodes and encapsulated in epoxy, metal cans etc.

thermal resistors

Other term for thermistors

1960s

When did thermistors become available?

thermistors

They are based on oxides of semiconductors.

TRUE

(TRUE or FALSE) thermistors are mostly NTC devices.

PTC thermistors

They are made from special materials. They not as common as NTCs, but they are advantageous when runaway temperatures are possible.

thermistors

They can be used in self-heating mode.

\-50°C-600°C

What is the temperature range of thermistors?

thermoelectric sensors

Among the oldest sensors. Discovered about over 150 years ago.

passive sensors

They generate electrical emfs (voltages) directly.

thermoelectric sensors

simple, rugged, inexpensive

0°C-2700°C

What is the temperature range in which thermoelectric sensors operate?

thermocouple

What is the fundamental device of thermoelectric sensors?

* metal thermocouples
* thermopiles
* semiconductor thermocouples and thermopiles
* Peltier cells

4 variations of thermoelectric sensors (HINT: MTSP)

Seebeck effect (1821)

It is the sum of Peltier effect and Thomson effect.

Peltier effect (1834)

It is the heat generated or absorbed **at** the junction of two dissimilar materials when an emf exits across the junction due to the current produced by this emf in the junction.