Can you give some more information as to the part number of the analog input card, and the wiring arrangement of the working vs non-working ones?
Not from my hotel room. I'm really not even responsible for resolving this problem, I was simply hoping to be helpful, and also hoping that this was a common enough problem that it would be recognized by someone more familiar with GuardLogix systems.
I do know that they are 4 point safety analog input modules, and that each input channel connects via a horizontal row of 4 terminals. Among these 4 terminals, I am told that the top terminal is for voltage inputs. We have only 4-20 mA instruments, so these terminals have no connections. Second from the top is the analog input positive terminal, whether connected to a 2 wire or 4 wire transmitter. Third from the top is the analog input negative for 4 wire transmitters. These are the input connections that do not work. They consist of flame detectors and pyrometers. The bottom terminal is a 24 VDC terminal providing loop excitation for our 2 wire transmitters, which all function properly.
The programmer saw no faults for the 4 wire transmitter channels yesterday during check-out, but when we applied a flame last night, the module LEDs indicated under-range on all of these inputs, although putting an amp meter in series with the circuit indicated valid current loop values of correct polarity ranging as high as 19 mA.
Our 24 VDC PS which powers our 4 wire devices (as well as our discrete IO, which functions with no problems) was originally floating, and we tried connecting 0VDC to earth ground, with no change in status. We even attempted to connect a hand held, battery operated signal generator to terminals 2 & 3 on these channels, but still showed under-range on the LEDs and no data. We can move a 2 wire transmitter to channels that don't work with the 4 wire transmitter, and they function properly.
I'm stumped.
