Archive for category Burner Control
Written by: A.J. Piskor
I was talking to a customer a few weeks ago, helping him with a Honeywell Flame Safeguard/scanner inquiry on a thermal oxidizer application. We started talking about the burner and he mentioned that he was tuning the burner based on the oxygen coming out of the stack.
This is a common practice for technicians working on boilers, radiant tubes, and immersion tube applications where 100% of the exhaust is coming from the burner and is not diluted by any process air. However, this is a bad practice to apply when working on an oxidizer, oven, dryer, or a multi-burner application.
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.”
More and more people are using Modbus to get data from their instruments and controllers back into their control systems for reporting, alarming and troubleshooting.
And while I can’t be there to help you set up your Modbus master, I can give you 13 rules and some general practice advice for communicating to any Modbus RTU device.
If you use thermocouples in high-temperature applications, you’re aware of the issues thermocouple drift can cause. Thermocouples drift. It’s not a question of IF, it’s a question of WHEN. And thermocouple drift costs processors time and money in processing errors, waste, downtime, and lost production.
Thermocouple drift occurs due to metallurgical changes of the metal alloy elements over the extended use of the sensor. Thermocouples can drift by as much as several degrees per year.
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?
Industry surveys say that nearly half of all processes aren’t accurately tuned. If you read my post on accuracy, stability, and repeatability, you’ll know that a poorly tuned process can result in bad readings, downtime, and wasted materials.
If you use a Honeywell UDC2500, UDC3200, or UDC3500 1/4 DIN universal digital controller, there’s a great built-in function called Accutune that can help make sure your control process is properly tuned.