Panelview 800 Issues

toddp65

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Aug 2014
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Florence, Ky
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So I'm running a glycol cooled vessel control system with a micrologix 1400 and a PV 800.

On the vessel screen is a numeric entry button to enter your desired setpoint and placed above it is the actual temp readout from the program. When you entered the desired setpoint, say 62 degrees (a window pops up and you enter the number thru the keypad) an hit enter, then 63 appears in the set point box (not 62). Several numbers do this-- the majority are the correct number but several don't. Example: 60-61, 62-63, 63-63, 66-66, 67-66... Not sure what to make of this situation.


Thanks
 
In the program how does ot work? does the HMI write the value to the PLC? what are the values in the registers in the PLC are they correct ?
 
The setpoint values are written to an integer for the PLC as a setpoint in LES and GRT states for controlling the glycol valves for the vessels. The actual variable is read from te PLC and it's an analog scaled. The setpoint is also scaled from the HMI using the built in scaling in the tag editior.

The system is at another facility so i can't see the actual register values. They would be in Celsius as they are converted in the HMI program.
 
Sounds like its displaying your scaled value and your scaling is a little off so rounding up or down, but this is just a guess, you need to look up the values in the PLC to see what is changing your HMI or the PLC and how it gets the values
 
Well the scaling is linear ...0-100 and 32-212...Not sure how some of the numbers are right and the others it rounds up...it doesn't discriminate between odd and even numbers...I'm not sure what it's doing. I'd have to see.
The write tag is the same as the indicator tag...I am assuming it's displaying what is being written?
 
You are seeing the results of rounding. Does the PLC control the valves or is there a PID controller in the mix too? Basically, these numbers are likely being truncated at some point in the math. I recently ran into this on a glycol system I did. You will have to change the math in the program to fix this.
 
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sparkie-- the PLC controls the valves--no PID--just on-off control. There isn't any math being performed at least by way of math instructions initiated or programmed by me. The program reads the analog inputs, SCP to a scaled valve and taking that value and comparing it to set point and opening or closing the valve if it's above the set point.

What math would you be referring too?
 
Well the scaling is linear ...0-100 and 32-212...Not sure how some of the numbers are right and the others it rounds up...it doesn't discriminate between odd and even numbers...I'm not sure what it's doing. I'd have to see.
The write tag is the same as the indicator tag...I am assuming it's displaying what is being written?

If you are entering the number, why scale it? (I see the 0-100 C = 32-212 F relationship, but why?)

Details are needed. What is the datatype of the setpoint? Integer or floating point? Exactly how is it scaled? Which HMI?
 
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If you are entering the number, why scale it? (I see the 0-100 C = 32-212 F relationship, but why?)

Details are needed. What is the datatype of the setpoint? Integer or floating point? Exactly how is it scaled? Which HMI?


The data is a degrees F on the HMI and coverts it to degree C for the PLC (the program and analog sensors are celcius--the operators wanted to read degrees F on the HMI.

The setpoint and actual temp are integers. As mentioned before, it's an Allen Bradley Panelview 800 programmed with CCW and a micrologix 1400


Thx
 
So are the numbers in the integers correct and only the display wrong or are both numbers wrong... if the numbers start out correct and they do because you set them with the HMI then they are set to the PLC where to the numbers go from correct to wrong? we know there is scaling and converting

What I would do is look at each location where the number is being used and follow it in the program from start (from HMI) to finish (back to HMI) to see where it goes 'wrong' and changes
 
I assume you are 'scaling' it using the tag parameters in the PV800? As others have mentioned you are seeing the results of rounding. The PV800 is scaling the integer and needs to round it then writes that value to your PLC. It then in turn reads that value for the displayed value.
You would be better off writing the setpoint directly to the PLC then doing the scaling to celcius in the PLC
 
Does the PV800's scaling function round or truncate? It seems, from what OP is saying, their numbers *may* be getting truncated instead of rounded. Also, I just wanted to know how you had it set up. Sometimes when you are reading from other devices, they will read, for instance, 305 as an integer, and that would be 30.5, so you divide by 10, to get the number into the correct format, but it can vary what happens to that .5. Some systems will round it, others will truncate it.
 
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On our glycol system we have a 2 degree offset in the program, maybe you have some sort of offset in it also. Our offset is changeable in the pv + or-10 degrees.
 
Digging this up because i finally needed to address this issue because the Brewers needed exact temperatures instead of a rounding temp. Apparently my PV 800 setpoints and actual temp indicators were programmed as real in the data type but the actual address entered was an integer in the program and a corresponding integer in the PLC program (all my doing--not sure why CCW didn't error informing me that N7:0 wasn't a REAL). After changing the addresses to reals in the PLC and the data type on the HMI to correspond with the chosen data type (Real), all is well and they get the exact number programmed into the numeric input on the setpoint.

Just thought i'd share this bit of realization on an error i created.
 

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