Archive for category Loop Controllers
People will fire up a new UDC 1/4 DIN loop controller, like a UDC2500 or UDC3200, and discover that the lower display periodically flashes an error code: UNPLUG. But what does it mean? Is something wrong?
A search of the pdf version of the manual hints that the Modbus Ethernet communications is involved:
The Ethernet status screen shows the network status of the Ethernet Link. This may be accessed either via Ethernet or via Infrared Communications. For example, if the Ethernet cable is unplugged, then the instrument cannot send up the EUNPLGED diagnostic message via Ethernet.
But the word UNPLUG is nowhere else in the manual.
Honeywell’s Process Instrument Explorer (PIE) configuration software used for configuring UDC controllers and the UDA analytical controller communicates with the instruments via RS-485, Ethernet, or Infrared (IR).
Since most newer PCs don’t ship with built-in serial ports to connect an IR adapter, you can use a USB-to-RS-232 converter, and then connect using the Actisys serial-to-infrared adapter (ACT-IR220L+). The USB converter will plug directly into your PC’s USB port, but install on a virtual COM port.
Here’s where it gets tricky: That COM port has to match the COM port used in PIE, and PIE doesn’t support ports above COM8.
You’ve heard this phrase before: “It’s simple. But nobody said it would be easy.”
And this is exactly one of those cases.
The Honeywell UDC3500 digital controller can support up to four setpoint programs, the ramp/soak profiles used in batch control operations. But after configuring all four profiles, I was stuck on how to select the one I wanted the controller to use.
There’s no “Program Select” button on the keypad. So I was mystified on how I was going to select my setpoint profile program #3.
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.