[ILM] 104B Flashcards
All types of controllers in closed-loop control systems have 3 subcomponents:
- sensor
- comparator/null detector
- transmitter
4 main types of sensors in HVAC/R
- temp sensor
- pressure sensor
- humidity sensor
- flow sensor
you MUST LEVEL the thermostat
T or F
True, since the transmitters are mercury bulb switches
fan cut-in & cut-out
cut-out(deactivate) to 80-90F
cut-in to(activate) 120-140F
flexible diaphragm
one of the most common applications for this sensor is as the combustion air proving control in a gas-fired mid-efficient furnace or rooftop unit
high-pressure limit
135F is usually adequate high-pressure protection for the high-pressure setpoint
- Low press control
- high press control
- either set
- high event = cut in
- high event = cut out
- high event first
transformers
provide an increase/decrease in control circuit voltage
relays
15amps and under
contactors
15amps and over
overload devices protect
the motor and final control devices
end-use devices ONLY
does not protect the electrical supply system of the wires bringing current to the equipment
overcurrent devices protect
the conductors powering machines from excessive heat damage from short circuits caused by excessive current conditions
Fuses protect
from overcurrent conditions
select and install fuses that are sized slightly below the maximum design current draw of any of the conductors in the circuit
T or F
True
single conductors have
a maximum load of 80% of 15A
0.8 x 15A = 12A is the max operating current load for the conductor
