Lab

Question 1

Mechanical principles can withstand?

Answer 1

Extreme or hostile environments

Question 2

Solid state construction is what then mechanical?

Answer 2

Less robust, are more accurate in temp sensing

Question 3

Solid state are used for?

Answer 3

For more precise controlled

Question 4

3 types of bi-metal sensing devices?

Answer 4

1- strip type
2-spiral type
3-disc type

Question 5

Strip type works by?

Answer 5

Two dissimilar metals welded together, the two metals expand and contract at different rates on cool or warm up, causing them to deflect. And arranged to either open or close on rise of temp.

Question 6

Spiral type is made/ works?

Answer 6

Made in a shape of spiral or coil

Question 7

Temperature sensing devices have two different applications. Some operate on…..and…..

Answer 7

-mechanical
And
-solid state construction

Question 8

What is the differential?

Answer 8

17 to 22degrees

Question 9

Thermocouple is a?

Answer 9

Flame proving device 26-32, produces voltage when heated. Has enough to hold in but not pull.

Question 10

A thermopile?

Answer 10

Use as a (TSD) as well as a power source. It is many thermocouples connected in series to make 800mv . Can hold and pull in.

Question 11

2 other types of temperature sensing devices?

Answer 11

• Bellows type

- liquid bulb type

Question 12

Bellows type are?

Answer 12

Use a small bellow…
Fluid inside either liquid or vapour.
Temp goes up liquid vaporizes expanding in the bellow and expand with pressure.

Question 13

Bellow types are commonly used for ?

Answer 13

This large movement is ideal for operating large snap action contacts. Such as those used in line voltage T-stat for unit heaters or electric heaters

Question 14

Liquid bulb type temp are used for?

Answer 14

For monitoring the temp of water and air in a pipe or tank. Measures temp

Question 15

Liquid bulb temp device is made of?

Answer 15

A rigid metal bulb attached to one end of a thin metal tube attached on other end. Liquid in diaphragm expands and contracts

Question 16

Thermistor is?

Answer 16

Solid state device in which resistance of semiconductor changes in response to temp.

Question 17

Thermistor has a what coefficient?

Answer 17

Negative, so increase in temp mean decrease in resistance. Accurate enough sense air temp in hearing cooling system.

Question 18

RTD (Resistance temperature detector)? Has what coefficient and is?

Answer 18

Has a positive coefficient. Physical appearance as a thermistor. An increase in temp results in increase in resistance. Platinum most common metal in RTDs chem resistant

Question 19

RTDS also can sense?

Answer 19

Greater accuracy then thermistor

Question 20

RTDs used for?

Answer 20

Suitable for industrial thermal processing

Question 21

Pyrometer?

Answer 21

Hot object emits radiation proportional to temp of a object. Measures radiation by use of focus lens concentrates radiation on sensitive thermocouple.

Question 22

Pyrometers can measure?

Answer 22

Temp as high as 4000•c can measure temp at a distance

Question 23

Pyrometer good for?

Answer 23

Measuring temp in industrial kilns and metal refining furnaces

Question 24

Control and settings are?

Answer 24

Temperature-sensing devices are used to ensure that acceptable limits are maintained.

Question 25

High limit control are for when?

Answer 25

A faulty blower or blocked cold air return can cause temperature to increase. Purpose is to shut off burner circuit.

Question 26

High limit control most commonly use ?

Answer 26

Disc type element cheap. Second is spiral.

Question 27

Set points?

Answer 27

High limit controls are usually set to open the circuit if temp exceeds a pre set value. Typically between 80 to 120•c

Question 28

High limit set •c
Max •c
Gravity furnace max

Answer 28

80-120•c
121•c
149•c

Question 29

Fan control purpose?

Answer 29

Start and stop a fan so heated air from the furnace is neither to hot or cold.

Question 30

What is a summer/ winter switch? Or manual auto switch?

Answer 30

Is a override switch that is connect in parallel with the fan control N.O. Contact. Allows to be independent from fan control