±«ÓãÖ±²¥

7800 SERIES RM7824A Relay Module

---

Installing Flame Detector

NOTE: Table 2 and Fig. 11 list the flame detectors available for use with the RM7824A. Make sure the correct combination of amplifier and flame detector(s) is used.

Proper flame detector installation is the basis of a safe and reliable flame safeguard installation. Refer to the instructions packed with the flame detector and the equipment manufacturer instructions.

Keep the flame signal leadwires as short as possible from the flame detector to the wiring subbase. Capacitance increases with wire length, reducing the signal strength. The maximum permissible leadwire length depends on the type of flame detector, leadwire and conduit. The ultimate limiting factor in the flame detector leadwire is the flame signal (see Table 6).

1>   FLAME DETECTOR LEADS ARE COLOR CODED. THE BLUE LEAD
MUST BE CONNECTED TO THE F TERMINAL AND THE YELLOW
MUST BE CONNECTED TO THE G TERMINAL. THE UV SENSING
TUBE IS POLARITY SENSITIVE. REVERSING THE LEADS EVEN
MOMENTARILY CAN DAMAGE OR DESTROY THE UV TUBE.

Fig. 11. Flame detector wiring.

OPERATION

Sequence of Operation

The RM7824A has the following operation sequence (see Figs. 12 and 14).

1>  MAIN FUEL VALVE WILL BE ENERGIZED DURING PFEP IF FLAME IS PROVEN.
2>   RM7890A1031 PFEP IS FIXED 30 SECOND.

Fig. 12. RM7824A sequence.

Fig. 13. Sequence status LEDs.

Initiate

The RM7824A enters the INITIATE sequence if the Relay Module verifies voltage fluctuations of outside 22 to 28 Vdc during any part of the operating sequence. The INITIATE sequence lasts for ten seconds unless the voltage tolerance is not met. When the tolerance is not met, a hold condition will be initiated and will be displayed on the optional Keyboard Display Module for at least five seconds. When the tolerance is met, the INITIATE sequence will restart. If the condition is not corrected and the hold condition exists for four minutes, the RM7824A will lock out. Causes for hold conditions in the INITIATE sequence are:

- Vdc dropout is detected.
- Internal timing functions are not synchronized.
- The noise that can prevent a sufficient reading of the low voltage inputs.
- Brownouts caused by low input voltage.

Fig. 14. LED sequence status display information (see Fig. 13).

Standby
The RM7824A is ready to start an operating sequence when the operating control input determines a call for heat is present. The burner switch, limits, operating limit control and all microcomputer monitored circuits must be in the correct state for the RM7824A to continue into the SAFE-START CHECK.

Normal Start-Up Safe-Start Check
The RM7824A verifies that a flame does not exist and proceeds into the ignition trial. If a flame is present, the RM7824A will recycle to the STANDBY period. If the critical loads are not in the correct state, a safety shutdown occurs.

Ignition Trials
Pilot Flame Establishing Period (PFEP):

1. The pilot valve and ignition transformer, terminals 8 and 10, are energized. The RM7824A has an intermittent pilot valve, terminal 8.