UDC 3300 and ST 800

I'm not sure if I can properly explain my issue. I do not have a lot of experience with plc.
We're using a Honeywell UDC 3300 on a Honeywell ST 800 pressure transmitter.
The ST 800 is replacing a ST 3000, which we were told was the modern replacement.
We keep getting INPT1FAIL, regardless of what we do. We've tried 3 transmitters, same thing. We've replace plc, same thing.
Wiring from transmitter to plc, good.
The only thing that changes is the read out is depending on which plc we use. either -30 or 300 inches. Normal operating range is 0-200 inches. We've alos replaced the circuit boards in plc.

Any thoughts?

use SFC for setup

An SFC (Smart Field Communicator) configures the ST800, which is not likely the problem. A UDC3300 input1 failure is either a misconfiguration of the UDC 3300 or no current through the 250 ohm dropping resistor across the analog input terminals, which could be an issue with DC power, loop wiring, or the resistor. A new ST700 transmitter is going to output a current if it's getting power and wired into the loop properly.

The UDC 3300 is really a PID single loop controller, it's not a PLC.

The UDC 3300 replacement, the UDC 3200, had its 10th birthday last March. The 3300 is getting gray around the muzzle. Are you sure the transmitter is the problem? Have you checked the loop power supply? No one messed with the configuration did they? Are you sure input 1 is still configured for 4-20?

A 2 wire loop powered transmitter (the ST3000, ST700) has 3 components in the loop:
- UDC controller (receiver)
- DC power supply
- transmitter

The UDC 3300 input 1wiring is shown below. Note the power supply in the loop and the 250 ohm resistor across the input terminals. Does your wiring match the diagram?



Some people use a voltage supply from the UDC, as shown below.





Either output could have gone 'poof' so it no longer outputs a voltage sufficient to drive the transmitter. If it were me, I wouldn't replace a UDC internal component for use as a loop power supply. I'd buy a DIN rail mount 24Vdc power supply and be done with it.

The 250 ohm resistor will drop from 1.0 to 5.0 volts as the transmitter ranges from 4.0 to 20.0mA (Ohms Law, E = IR), so you can measure the voltage across the resistor to see if it matches with the transmitter output. No voltage drop means no current; something's wrong.

Thanks for this information. I will go over this with our maintenance tech tomorrow and see if this helps figure out our problem. I'll update tomorrow
Thanks again

Update:
We've gone through the info provided, everything from that standpoint checks out. We believe the transmitter is fine and we are missing something in the setup/configuration.
We're simply measuring a column of liquid. There is an aspect of vacuum, but this compensated at the level transmitter.
We've removed transmitter leads and calibrated as 0% range value ( 0mA). We have vessel above operating level and have calibrated that as 100% range value. We input configurations. The results are a level reading of 300 regards of level change in vessel.

Make sure the transmitter is connected to the left pair of the three terminals, circled in red in the illustration. The test terminal does not source current.

We're good there.
We're going back to set up our high range by exceeding our operating level, then bring level back to see if readout level drops.
We're pretty sure we're missing something in the set up.

"The results are a level reading of 300 regards of level change in vessel." You've said.
I assume you've put a meter in series with the loop at that time and confirmed your
m.A.'a are rising and falling with your water column?

"removing the transmitter leads to get a 0 m.a. signal for your zero." You stated.
Does your read-out reflect this as it should when 0 mA are flowing? and

"The results are a level reading of 300 regardless of level change in vessel." You stated.
Are the millia-amps in your loop reflecting the change when you either have or simulate this "level change in vessel"? Just trying to confirm here that when you vary pressure, (height in your water column), you ARE seeing a corresponding milliamp change confirming that your read out IS seeing the milli-amp change that exists but not giving a proper read-out; and there-fore likely a scaling / parameter issue;
OR
when in operation, the readout is stuck at 300 because your milli-amps aren't dropping below 20 for a number of other reasons. (Plumbing, various orifices not in proper open or closed position, wiring issue etc...)

Unless I missed it, I saw nowhere in the post that the milli-amp loop was rising and falling as per the column...

Good luck in either case,

1) You started out with "input fail" error. Is that corrected? Do you have a readings on the UDC?

2) What is the ST7/800's LRV (lower range value, 0% range value) setting?

3) What is the ST7/800's URV (upper range value, 0% range value) setting?

4) Do these transmitters have capillaries and seals connected to the transmitter or are they standard DP transmitters with 1/4" NPT threaded connections?

5) What is the specific gravity of the stuff in tank?

6) Attached is an excel spreadsheet for the UDC 3300.
Please go through it, fill in the blanks and post it back here with some change in the file name.

7) > calibrated as 0% range value ( 0mA)
That makes no sense. A loop powered transmitter's minimum output is always 4.0mA. 0mA means the transmitter is not working in the circuit. 4.0mA from the transmitter is typically zero elevation (0% range value) in a level application.

When the UDC INP1 TYPE is 4-20mA and there's a 250 ohm resistor across the input terminals, then the following settings
- IN1 LO should be 0.0 for 0% range value
- IN1 HI should be the transmitter's URV (in wc)/specific gravity, or that value scaled by the volume or weight conversion factor if you do level in volume or weight.

Yes,
I think he

"disconnected the transmitter lead" to get the erroneous 0% range value of 0 m.A.

which, as you said danw, should and will be 4 m.A. when it's hooked back up and the liquid column is 0 of 0-200 inches and the system is configured, wired, plumbed and consequently functioning properly. (4mA=0, 12mA=100", 20mA=200" in this linear application.) I just had yet to see, but perhaps missed it, that any varying mA were flowing corresponding to the column change.) Giving rise to a number of fundamental wiring or orifice positioning concerns, No doubt a comprehensive spread sheet should isolate the issue

Good luck guys. : )