Assessments - 3, GPA: 4 ( )

Fabricante : A.O. Smith Arquivo Tamanho: 796.44 kb Arquivo Nome : Língua de Ensino:

In standby mode the display shows the temperature screen and in fault mode the current error screen is displayed. 4. The system then compares the temperature read from the controlling probe (inlet or tank) to the setpoint temperature. If the temperature is less than the operating setpoint minus the differential temperature and the thermostat input is closed then a call for heat is established and the system shifts to the run mode (green "Running" LED turns on). 5. The heating sequence begins by applying power to the pump and, if selected, the powered vent and the IRI gas valve. 6. After a few seconds the blowers are turned on for 30-second pre-purge period of combustion chamber. 7. The stage one igniter is turned on. 8. After the igniter has reached a minimum of 2.8 amps, the gas valve is energized to allow gas flow to burners. 9. After an additional one second, the system checks the status of the flame through the flame rod (sensor). If the flame is not verified within 4 seconds, the gas valve is immediately shut off 37 followed by 15-second inter-purge period, then the system returns to step 7, if the "Trial for Ignition" dipswitch is set for three (3) tries. If the dipswitch is set for one (1) trial, the system will declare an error and boiler will require resetting the control. 10. If a flame is detected, stage two will be activated and start its blower. Once the blower air has been proven, igniter two will begin trial for ignition cycle as above, (this is not the case for model 1000, which has only one igniter). 11. Stage three will activate upon flame detection on stage two. The gas valve will open five seconds following call for heat and gas flow will continue if flame signal is detected. (On 4stage firing system, the blower associated with stage three will start and once the blower air has been proven, the ignition cycle will take place as above. If flame is not proven, a 15second inter-purge period will be activated followed by another trial for ignition). 12. All stages will remain running until the set point for a given stage is satisfied. The last stage will drop out first followed by inter- stages then stage one will drop out last. Note: Once a stage is satisfied, the blower associated with that stage will continue for 15-second post purge period. 13. Once all the stages have been satisfied, the boiler pump will continue to run for the programmed post-circulate cycle. 14. The control now enters the idle state as displayed by the "Standby" LED. The control will continue to monitor heat demand and state of other system devices. Upon a drop of water temperature below the set parameters, the control will return to step 5 and repeat the entire operating cycle. Note: Any fault detection, during standby or running modes, will halt the heating sequence and shift the system to the service mode where the detected fault will be displayed. NOTE: In standby and running modes the system constantly monitors the signals and the internal operation for faults. Any detected fault will halt the heating sequence and shift the system to the service mode, where the detected fault will be displayed. Temperature Setpoints (System Control Algorithm) The boiler has a hysteresis type control, which means that it will begin heating the water when the temperature sensed by the control probe (inlet or tank) falls below the operating setpoint minus the differential setpoint for stage 1. It will stop heating the water when the temperature rises to the operating setpoint. If the system has multiple stages then the differential setpoint for each stage is also subtracted from the operating setpoint. The following examples will further explain this operation. Setup: 2 stage system, operating setpoint - 140, stage 1 to 2 differential setpoints = 10. Example 1. Temperature begins at 150 and drops to 90, see Figure 20A. At 140 the system remains in idle mode. As the temp drops to 130 (140-10) stage 1 turns on and stage 2 remains off. At 120 stage 2 also turns on. Example 2. Temperature begins at 90 and rises to 150, see Figure 20B. At 100 both stages are on. (This is the case when a boiler is first started and the controlling temperature is below the operating setpoint minus all of the differential setpoints. At that time both stages are turned on, in sequence from 1 to 2. At 130 stage 2 turns off. At 140 both stages are off. Stages 1 and 2 will turn on in sequence from 1 to 2. FIGURE 20 A. FIGURE 20 B. UIM OPERATING PROCEDURES FIGURE 21. UIM, USER INTERFACE MODULE The UIM receives commands from the user and displays operational information to the user via an LCD (liquid crystal display) up to eleven LED's, and five touch switches. The LCD provides information to the user by the use of 10 menu-activated screens. Within each of the screens, helpful information can be displayed by pressing the "Help" button. The LED's visually inform the user about the mode the system is in. The touch switches allow the user to control the operation of...

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