Posts Tagged loop controller
Written by: Dan Weise
Good news! Recent upgrades to Honeywell’s HC900 Process and Safety Controller includes a major update to analog/loop processing speeds. Even though analog/loop cycle time has been 500mS since the early 2000s, early versions of the HC900 controller were only capable of a processing speed of 2x/second.
The upgrade to the HC900 CPU’s microprocessor hardware and an associated firmware update broke that processing speed limit for their SIL-rated CPUs. Honeywell C50S and C70S model CPUs v6.1 will now process analog inputs and loops at a rate of 10x/second (100mS per update). If your process needs additional analog/loop throughput speed, you will benefit from these enhancements to the HC900 systems.
To run at 100mS, a qualified hardware configuration is required:
RTDs are great temperature sensors – accurate and easy to install. But they are not friendly when it comes to trying to get a single RTD to go to two places, like when an RTD temperature measurement has to go to both a controller and a recorder. People call and ask, “How do I split an RTD signal?” The short answer is, “You can’t.”
An RTD cannot be wired in parallel or in series to a second device. Any RTD input supplies a known, regulated ‘excitation’ current to the RTD. Mixing RTD inputs would mix currents and that’s a Big No-No.
There’s also a lead wire compensation circuit for 3- or 4-wire RTDs that would create problems if a single RTD were connected to two different RTD inputs. There’s just no feasible means of making two RTD analog inputs play nice together.
But all is not lost. There are several ways to achieve your goal.
A customer has several UDC 3200 loop controllers with newly added Ethernet cards. He needed to configure each of the controllers’ IP addresses using Honeywell Process Instrument Explorer (PIE) software. Because the controllers are working in a 24×7 continuous process, he was concerned about how making those changes would affect each controller’s performance.
So he asked me: Would a PIE action of uploading config files from or downloading them back to a controller affect the controller’s performance?
In the past, I’d only ever changed a controller’s IP address when it was on my workbench, not when it was actively controlling a process. So I’d never paid attention to whether PIE communications would affect the controller’s output or its PID action. Since I couldn’t answer the question, I told the customer I’d run a test to find out for sure.