Controls Ft. T Frank Flashcards
What does a closed loop control circuit do
Uses feedback to make control system automated
Purpose of an automatic gas valve
- comfort
- safely
- economy
- convenient
What does a pressure transducer sense?
Pressure than coverts to electrical signal
On a A19 temp controller feat position is B in?
Closes on a rise in temp heating
What does an anticipator do
Creates false load to prevent overshoot
Like voltage thermostat can be temporarily used in a millivolt application?
Yes
What’s in a mercury bulb thermostat
Bimetal coil and contactor
-must be carful levelled
Strip type sensor is used for what
Electric baseboard heating
- no anticipator
Natural gas “WC?
3.5”
How much power does a thermocouple make
30mv DC
What kind of power does flame rectification create?
DC micro amps
What is an anticipator in heating
A resistance wire in series with thermostat contacts
In heating is anticipator energized in the off cycle
No
Thermistor change in temp=
Change in resistance
Negative temperature
2nd Series if events for hearing
Pre purge
What makes a spiral sensing element more accurate
Increase length
Setting at LPC how long do you watch it for?
What temp can it not go below
2 cycles
33.5F
Direct Spark or hot surface igniter use flame rectification?
Yes
Is a resistor temp detector more accurate than a thermistor?
Yes
Can be positive or negative
A-19 is snap acting? Why?
Yes to avoid arking
How is an anticipator wired in a cooling cycle
In parallel
When does a constant cut in control cut in?
38F or 41F
Combination gas valve, must must be held open manually when lightning pilot?
Yes
When does the fan shut off
90-100F
Igniter warm up period?
17 seconds
Do millivolt thermostats have anticipators?
No draws too much voltage drop
What does open loop mean?
No feed back
Operates by time
Power goes from where to where in furnace ac control
In from R to Y though the CC than to C
Disadvantage of pump down?
Compressor could short cycle
Ex. Leaking solenoid, improperly set LPC
Dry bulb is effected by
Humidity
Air movement
Radiation
Yes
When does the fan turn on?
120-140F
How long does inducer motor run after blower off?
15 seconds
Call for heat terminals
R and W close
Approximate settings if a high limit switch in the high voltage circuit?
180-200F
Blower off delay what terminals?
Cr and W open
Combination gas valve, how much power does the main valve need?
24VAC
What is LVT cable
Extra low voltage cable
For thermostat wiring
Why is a jumper factory installed
When cooling and heating use same control voltage
Advantages of pump down?
- No flooding the comp
- very good liquid refrigerant control
I’m cooling when is the anticipator energized?
On the off cycle
Combination gas valve, what is powers by the thermocouple
- safety
- power unit
- pilot start
What’s in a combination gas valve?
- Regulator
- safety valve
- power unit
- main gas valve
- manual gas shut off
What temp does AHRAE recommend for cooling
75F for cooling
Does power from a thermocouple open the pilot valve?
No only holds it open
What class of transformer do most furnaces have?
Class 2
With a F-140-20 disk type overload what does the 140 mean and 20
140 is cut out
20 is differential cut in
Checking volts in electrical circuit
Power is on and Meter in parallel
Motor starters and contractors are different because
Motor starters have overloads
Ad stages of hot water heating
Less space
Less air movement
Hot water disadvantages
No ventilation
No air filtration/humidity control
What so zone thermostats control
A pump or valve
On mid efficient furnaces they need to maintain return water temp of ______ to prevent condensation
130
Hot water, .43 psi pressure drop for upwards piping
Yes
Can a mop txv and a cpr be together
No
High limit is set at what fir hot water application
210F
Hot water uses float type and electric for
Proving water flow and low water cut out
Hot water expansion tank w no bladder is called a
Compression tank
Make up water regulator is set between
10-25 Psi
Can zone valves be power open abs power closed
Yes
Transformer can only be loaded to
80%
