Posts Tagged combustion control
A typical combustion system is complex to say the least. It is usually made up of various devices from multiple vendors that have to be combined and connected in order for the system to work. These systems are not typically flexible and are hard to change once the system has been set up.
Honeywell has come up with a completely new system that provides limitless flexibility with fewer components. This product has been designed as a fresh start for the combustion industry or in Honeywell’s words, “It’s time to wipe the SLATE clean.”
This one qualifies as a “Page the manufacturer left out of the manual”, and was brought to my attention by a customer who was having problems with remote reset on his flame safeguard system.
A typical multi-burner furnace has Honeywell 7800 flame safety controls on each burner as shown below. Modbus is used to fetch fault codes for the plant’s HMI system, and to allow the control system to remotely reset the flame safety controls.
The reported problem was that Modbus did everything as advertised except remote reset on the one control that had a S7800A keyboard display module attached (colored orange in the network image on the right, or as shown in the controller image below).
That unit would only do a reset when an operator pressed the reset button on the RM7838C controller. Modbus failed to get the controller to execute a remote reset.
The problem wasn’t communications – all Modbus read functions worked and Modbus writes to all the other controls worked as expected. But somehow, the write command to do a reset action was ignored by the S7800 keyboard display.
So, what’s causing the problem?