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State of the Art Burner Controls: Honeywell RM7800 Series

Every service company that works on commercial burners has experienced random lockouts with burners.

A service technician arrives at the job and finds a Honeywell R4795 primary control on the burner.  He visually inspects the burner and doesn’t find any obvious defects.  The technician resets the R4795 to take it out of the lockout condition and initiates a call for heat.  The burner functions perfectly.  He plugs in his flame meter to check for a good, bad, or marginal flame signal and initiates another call for heat.  The burner lights off and runs perfectly; the flame signal is strong and steady.  He cycles the burner 20 times.  Nothing goes wrong and he can’t find anything wrong. 

If an RM7800 series control had been on the job, the scenario may have been like this:

The technician arrives on the job.  He finds an RM7895 Honeywell relay on the burner.  He snaps in a S7800A display module and scrolls through the diagnostics and finds out the Airflow Switch (AFS) has caused the last six lockouts by opening during the run cycles.  He knows the number of the cycles when the AFS opened, the number of hours of run time each time it opened, the status of all the terminals, in short, all the information needed to diagnose, quickly diagnose, the problem.  He now knows what causes the burner to intermittently shut down and lock out.  He found all this out in about 30 seconds, without once having to cycle the burner.  He can now be confident he can “fix” the burner.  Which do you want to do?  Guess at what may be wrong, or know what is wrong?

The Honeywell 7800 series controls are the latest state of the art burner controls designed to replace all old mechanical controls made by Honeywell or others.  The 7800 series controls numbering system corresponds to Honeywell’s old mechanical controls numbering system.  The last two digits of the model numbers are the same.  An RA890 is an RM7890, and R4140 is an RM7840, etc.

                                              Honeywell 7800 equivalents for Fireye are:

                                              UVM-1D, TFM-1D = RM7890’s

                                              UVM and TFM 2, 3, 5 = RM7895’s

                                              D Series = RM7840’s

                                              E Series = RM7800’s

Of course, all controls can be upgraded.  An RM7800 can certainly be used for a D series.  An RM7800 is an RM7840 with the display, S7800, included.  All the 7800 controls can use the S7800 display, but only the RM7800 and RM7838 include the S7800 display module.

All 7800 series flame amplifiers interchange for all the 7800 controls.  Simply match the amplifier to the scanner being used.  The amplifier will fit any 7800 control.  The flame signal is now measured in volts D/C, not milliamps.  The S7800 will display the flame signal in V/DC, and a DC voltmeter can be plugged into flame jacks on every amplifier.  Proper flame signal is a minimum of 1.25 V/DC.  The S7800 display will display flame signals up to 5 V/DC.  Seldom will any flame signal exceed 5 V/DC.

Fifteen different timings for purge cards are available from 2 seconds to 30 minutes.  Like the amplifiers, the purge cards fit all the 7800 devices that use purge cards.  The code requirement that four air changes pass through the burner before ignition is allowed can be easily met with the 15 timings available.

All the series 7800 devices use the same sub-base, the Q7800.  The Q7800A is two-sided for use in burner panels.  The Q7800B is four-sided for wall or burner mounting.  While usually mounted vertically, the 7800 controls can be mounted in any position except horizontally pointing down.  Only two screws hold the relays to the sub-base.  The 22 terminals on the sub-base are of the knife blade style, making the installation of the relays to the sub-base quick and easy.  For wiring the sub-base, each terminal number is cast into the plastic holding the terminal.  There is also a thin plastic sheet at the bottom of the base with terminal numbers on it.  Each terminal can hold up to two #14 size wires.

                                    Four terminals are always wired the same.  They are:

                                        L2  -   Always the neutral of 115VAC (-)

                                        22  -   Shutter drive for self check scanners

                                        F    -   Flame scanner wire (also labeled 11)

                                        G   -   Ground for scanners

G terminal is connected to a large green ground screw to ground the control to a good earth ground.  It is important that 7800 series controls are well earth grounded.  The use of the rest of the terminals will vary, according to the relay used.  i.e., using an RM7890 terminal 3 is the connection for 115VAC hot (+).  Using a RM7800 or 7840 terminal 4 is 115VAC hot (+).  Follow the wiring diagrams for each primary or programmer to determine proper terminal usage.  Snap off covers on the sides of the Q7800’s give easy access to the terminals for testers, even with the relay on the sub-base.  Test probes fit neatly and easily into slots to make contact with the terminals.  Selection of the components to complete a system is made easy by the attached charts.

The 7800 Series is microprocessor-based control, factory programmed for burner sequencing, flame supervision, system status indication, and stores an immense amount of information in its memory, all of which is retrievable by using the S7800 display module.  The S7800 display module can retrieve the complete burner controller data:  sequence status, sequence time, hold status, lockout alarm status, flame signal strength, total hours of operation, total cycles of operation, and if an expanded annunciator is connected, its status.  The display can be scrolled through the history of the six most recent faults showing cycles of operation at time of fault, fault message and code, hours of operation at the time of fault, sequence status at time of fault, sequence time at time of fault, and if an expanded annunciator is connected, its data at time of fault.  Diagnostic information includes the device type, flame amplifier type, flame failure response time, manufacturer code, on/off status of all inputs and outputs, pre-purge time selected, software revisions, status of configuration jumpers, and the status of the run test switch.

The S7800 can be remote mounted, if desired.  Remote reset of lockouts can be accomplished through the S7800 or by using a S7820 installed on the 7800 series relay.  A simple two-wire hookup using a momentary pushbutton is all that is required.

The S7830 is an enhancement module for use with any 7800 series relay.  It is designed to monitor a series string of limits, controls, and interlocks.  Twenty-one monitored contact points can be added.  A red LED identifies visual indication of the string of contacts.  When power is present at the contact, the LED is illuminated.  When the contact is de-energized, the LED is dark.  If the contact is identified as the first out annunciation point, the LED will flash.

All 7800 series controls go through a 10 second initiate period when first powered up.  The power LED will be “on” during this time.  After initiate, the power LED will blink.  During initiate, the relay is verifying line voltage and frequency.  If they are not within tolerances (+10/-15% for voltage, + or - 10% for frequency), the control will “hold” until tolerances are met and then begin initiate again.  If “hold” lasts for four minutes, the control will lockout.  Once through initiate, the control goes to standby, waiting for a call for heat.  Most 7800 series relays have 1, 2, or 3 configuration jumpers.  These jumpers can be left intact or cut as desired.  Each jumper is clearly labeled as to what its function is, if left intact or cut.  Once cut, a jumper cannot be restored.  Cutting a jumper by mistake does not disable the control!  Cutting a jumper enhances the level of safety.  The cut jumper with its resistor should be removed from the relay.

The 7800 Series of controls can communicate with an IBM or IBM compatible personal computer.  A PC can communicate with up to 1000 sites.  Each site is a Q7700 communications interface base unit that can hold up to six QS7800A modules.  This means that one PC can monitor up to 6000 burners.

For communications with a PC, the 7800 relay will need either an S7800 display or S7810 data control bus module, a Q7700 base unit, a QS7800A module for each burner, and the ZM7850 software package.  The PC does not need to be dedicated to only the 7800 series control monitoring.  Other programs can be running on the PC.  The computer will “beep” to show something coming in from a 7800 when other programs are running on the PC.

For local communication, the PC must be within 50 feet of the Q7700, but the Q7700 can be up to 4000 feet from the 7800 series relay.  Remote communications require a modem.

Some additional information that is not mentioned or is not clear in the available literature on the 7800 series is:

Every 7800 relay goes through a safe start check on a call for heat.  This takes less than a second.  The output terminals are turned into input terminals and “look” for 30 volts or more on each terminal that is not supposed to be powered at that time.  If it finds 30 volts or more, the control will lockout.

Relays with configuration jumpers can have the jumpers left intact or clipped up to two hundred hours of run time.  After two hundred hours, the jumper configuration is locked into the relay and they can no longer be changed.

The attached form 65-0118-1 “7800 Series System Annunciation Diagnostics and Troubleshooting” should be studied.

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