sensors

Question 1

orifice flowmeters

Answer 1

a single point of resistance provides a pressure drop from which flow can be calculated. When gas travels through, it pushes open and open the flap. As it bends with more flow (and less with less flow) we measure the pressure drop from P1 to P2.

Question 2

ultrasonic flowmeter

Answer 2

ultrasounds wave shot through medium (gas flow) and time it takes to return is influenced by the velocity of gas. Detected via
transponder and receivers.
Advantages: No mechanical parts, no resistance imposed, not affected by extreme temperatures or gas composition
–less accurate than other methods

Question 3

hotwire anemometers

Answer 3

Wire is heated, temperature maintained/measured within a narrow range. Heat lost is in proportion to flow = more flow = more heat loss, need to maintain more voltage to maintain temperature. Voltage can be mapped across range of flows. As gas passes by it cools the wire. Either measuring how much current it takes to keep the wire that temperature - how much flow going across the wire.
Advantages: Good accuracy, high sensitivity at low flow rates (good for babies), short response times
Disadvantages: Fragile, easily soiled, condensation (high humidity can affect fxn)

Question 4

pneumotachographs

Answer 4

Linear resistance creates pressure drop by measuring pressure on both sides a flow can be calculated. Resistance increases as flow increases. Sensor inside causes digital/electric signal to tell vent of pressure drop and calculates flow.
Advantages: Accurate, compact, short response time, mostly linear response (more accurate across wider range of flows (slow/fast))
Disadvantages: Not accurate in odd gas mixtures (ie Heliox), temperature extremes, less accurate at very high flow rates.