Honeywell AUTOMATIC CONTROL Engineering Manual page 157

Step 3—Write a detailed sequence of operation for the process.
The hot water pump starts anytime the outside air
temperature drops to 52F, subject to a software on-off-auto
function.
When hot water pumping is proven by a current sensing
relay, converter controls are energized. Hot water temperature
setpoint varies linearly from 120F to 170F as the outside air
temperature varies from 60F to 0F. The converter steam valve
is modulated to maintain a converter leaving water temperature
according to a varying setpoint schedule.
The steam valve closes anytime hot water pumping is not
proven and anytime the valve actuator loses motive power.
Step 4—Develop the detailed flowchart.
Step 5—Write the program.
See the Air Handling System Control Applications section
and the Chiller, Boiler, and Distribution System Control
Applications section for other examples of Microprocessor-
Based/DDC systems.
MICROPROCESSOR-BASED/DDC FUNDAMENTALS
START
O.A.
TEMP
NO
EQUAL TO OR
BELOW
11°C
YES
PUMP
ON?
NO TURN
PUMP
OFF
CLOSE
STEAM
VALVE
END
Fig. 18. Flowchart Example.
147
ENGINEERING MANUAL OF AUTOMATIC CONTROL
YES
NO YES
PUMP
ON?
START
CONTROL
PUMP
SYSTEM
ENERGIZED
NO
ENERGIZE
CONTROL
SYSTEM
CONTROL
SYSTEM
MAINTAINS
RESET
SCHEDULE
M13120
YES