Instrumentation

Front 1

elevated zero

Back 1

zero is above the lower range value

Front 2

accuracy

Back 2

the degree to which the output approaches true value

Front 3

range

Back 3

the extremes of the quantity being measured

Front 4

basic types of measurement

Back 4

direct

indirect

Front 5

block diagram of a basic instrument channel

Back 5

process-detector-transducer-amplifier

-transmitter-remote indication or control device

Front 6

functions of a temperature detector

Back 6

alarm

indication

control

Front 7

alternate methods of determining temperature

Back 7

use a spare detector - dual element RTD

pyrometer - portable thermocouple

Front 8

environmental conditions affecting accuracy of temp. detection

Back 8

temperature - affects the resistance of components and calibr. equipment

humidity - moisture collets and causes short circuits and corrosion

Front 9

Reference accuracy

Back 9

a number or quantity that defines the limits that errors will not exceed

Front 10

bimetallic strip thermometer

Back 10

2 strips of metals with different thermal expansion coeficients are joined together forming a spiral. One strip expands more than the other

Front 11

thermocouple

Back 11

-2 wires with different THERMOELECTRIC difference

copper/nickel chromium/nickel platinum/nickel

Converts thermal energy into el. energy

When heated, electrons start to flow from one wire to the other, from Cu to Zn, creating voltage. More heat = more voltage; voltage diff. between the heated end reference end

Front 12

pressure detection functions

Back 12

alarm

control

indication

Front 13

bellows-type pressure detector

Back 13

0.5 - 75psi (with spring up to 1000psi)

metallic bellows expands or contracts depending on applied pressure, must always be opposed by a spring

pressure reading either direct or an el. signal

Front 14

bourdon tube type

Back 14

thin metal tube bent into an arc, when pressure is applied, the tube tends to straighten = pointer movement

Front 15

D/P cell

Back 15

Diaphragm or bellows type pressure gauges connected between two points in a system

- used to measure flow, pressure and level

- equalizing valve for removing the instrument from service, it's connected between HP and LP. When the eq. valve is open it equalizes the pressure across the D/P cell = produces minimum pressure and yields low DP cell output

Front 16

gauge glass

Back 16

- transparent glass tube on the outside of a tank

- same level of liquid in the tube as in the tank

- cons: debris obscuring the glass = hard to read, gasket failure

Front 17

ball float

Back 17

a hollow metal ball or sphere connected to a rotating shaft with a pointer at the end

cons: ball may sink=low reading, mechanism may jam, operation within +- 30deg rotation=smaller level changes

Front 18

chain float

Back 18

- float up to 12" dia, the range of level is only limited by the size of the vessel

- float connected to a rotating mechanism and a weight

- cons: may jam, float may sink = low reading

Front 19

Dip tube (bubbler)

Back 19

- a vertical pipe with a constant air flow connected to the tank through the side at the bottom to displace water in the pipe. The pressure required to displace the water determines the level in the tank

Front 20

D/P Cell level detector

Back 20

- measure the difference between a known pressure and variable pressure sources (the known pressure can be atm., hydrostatic or system)

Front 21

open vessel DP cell detection

Back 21

HP side senses the pressure at the bottom of the tank, LP side is vented to atm. pressure

Front 22

closed vessel DP cell detection

DRY reference leg

Back 22

the reference leg is pressurized with gas and connected to the LP side (area above the level of liquid in the tank); HP side is connected to the bottom of the tank sensing the hydrostatic pressure

Front 23

Wet reference leg

Back 23

- for applications with condensable liquids

- the reference leg is filled with the same liquid as the tank and kept full at a constant level by a condensing pot

- the reference leg is connected to the HP and tank to the LP side

Front 24

Flow sensor purpose

Back 24

measure of quantity of fluid past a point per unit time

Front 25

orifice plates

Back 25

- mounted between a pair of flanges creating a low pressure downstream

- cons: erosion on sharp edges and very high permanent pressure drop

Front 26

venturi tube

Back 26

- necked down tube causing low pressure downstream
- no sharp edges = smallest unrecoverable pressure drop

Front 27

flow nozzle

Back 27

- simpler and less expensive than venture

- for high velocity flows

- unrecoverable pressure drop is comparable to the orifice

- used for fluids that contain small particles

Front 28

elbow meter

Back 28

- used to monitor pump flow at the pump suction elbo

- low cost, simple, measure flow in both directions

Front 29

pitot tube

Back 29

- measure fluid velocity instead of flow rate

- also used to produce DP for flow detection

Front 30

environmental concerns for pressure detection

Back 30

ambient temperature, humidity and atmospheric pressure

Front 31

environmental concerns for flow detection

Back 31

ambient temperature, humidity and density

Front 32

rotameter

Back 32

- rotating float in a conical glass container mounted so that moves vertically and has minimal friction

- expanding conical shape

- the higher the fluid is in the container the more volume and less density it is

Front 33

Ionization smoke detector

Back 33

- an early stage detection (incipient)

- the combustion products of the early stage of fire will pass through a fixed beam of radiation, causing more particles to be ionized, increasing the output current of the chamber

Front 34

photoelectric smoke detector

Back 34

- smoldering stage detection

- LED generates light that under the normal conditions does not reach a photodiode installed on the opposite side of the chamber. When smoke is present the light will be scattered so that the photodiode will receive some light signal and generate el. voltage

Front 35

Thermal fire detectors

Back 35

- detect heat from an actual fire at the flame stage

- as temperature increases, the resistance of the thermistor decreases

- it responds quickly