adccommunitymod (AutomationDirect) asked a question.
Created Date: April 23,2018
Created By: tpeery
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This is the second Click PLC Project and it is nearly a duplicate of the first project. The first project is working and has been since installed. I have used like products on both projects, this includes the Click PLC, the larger power supply, two RTD input cards and one 4-channel Analog input card. The second project has an additional 24 vac input card. I have not began to stress the 1300 ma power budget having only exhausted 210 ma. Both projects are using a Vaisala Temperature and Humidity sensor with 4-20 ma out. The first project the scaling was set on the Vaisala inputs and it has worked well for a year, communicating this data the a C-more panel. I used the same method to set the scaling on the second project and all seemed well. Then I noticed that the temperature started climbing. I am simply measuring the temperature next to an HVAC Thermostat so I have an immediate cross reference as to the accuracy. The Stat is not changing. I replaced the Vaisala with an identical sensor. The reported milliamp at the System Monitor did not change. It continued to be too high. So I then placed the Analog input card on an isolated power supply. The milliamps did not change in that they continued to be too high. So I ordered a new C0-04AD-1 analog card. After it was replaced I had to set the scaling and it was working fine for about twenty four hours. The reported temperature and related milliamps continue to climb. The temperature range it the Electrical Cabinet where the click is installed had ranged from 40 degrees F to 85 degrees F during this time span but I do not find a correlation between this and the reported temperature increase of the monitored area. I am hoping that someone may have experienced this problem and can offer solutions because I am lost. Just a note the other input monitoring humidity also climbs reporting a false reading of RH.
Created Date: April 23,2018
Created by: tpeery
This is the second Click PLC Project and it is nearly a duplicate of the first project. The first project is working and has been since installed. I have used like products on both projects, this includes the Click PLC, the larger power supply, two RTD input cards and one 4-channel Analog input card. The second project has an additional 24 vac input card. I have not began to stress the 1300 ma power budget having only exhausted 210 ma. Both projects are using a Vaisala Temperature and Humidity sensor with 4-20 ma out.
The first project the scaling was set on the Vaisala inputs and it has worked well for a year, communicating this data the a C-more panel.
I used the same method to set the scaling on the second project and all seemed well. Then I noticed that the temperature started climbing. I am simply measuring the temperature next to an HVAC Thermostat so I have an immediate cross reference as to the accuracy. The Stat is not changing. I replaced the Vaisala with an identical sensor. The reported milliamp at the System Monitor did not change. It continued to be too high. So I then placed the Analog input card on an isolated power supply. The milliamps did not change in that they continued to be too high. So I ordered a new C0-04AD-1 analog card. After it was replaced I had to set the scaling and it was working fine for about twenty four hours. The reported temperature and related milliamps continue to climb.
The temperature range it the Electrical Cabinet where the click is installed had ranged from 40 degrees F to 85 degrees F during this time span but I do not find a correlation between this and the reported temperature increase of the monitored area.
I am hoping that someone may have experienced this problem and can offer solutions because I am lost.
Just a note the other input monitoring humidity also climbs reporting a false reading of RH.
Created Date: April 23,2018
Created by: RogerR
If multiple devices have the same problem, it may be the commons or grounds not connected well or together between devices.
A poor connection can cause a common/ground to float or the potential between two devices not the same.
Created Date: April 25,2018
Created by: tpeery
RogerR, Thank you for the reply. I added another ground wire from the Rhino power supply that is serving only the Analog card to the common ground that is connected to the 24 vdc power supply that serves the PLC. It has been 24 hours and the temp continues to climb on the Cmore display. As well the Ma reading on the input card as viewed through the system monitor has increased from 9.6 Ma at 70 degrees F 24 hours ago to 10.1 Ma at 70 degrees F at present. 10.1 Ma displays as 75 degrees as related to my scaling factor.
If history repeats itself the Ma input and the display will continue to climb ever so slowly. I have used an Automation direct 3-wire unshielded conductor to connect to the sensor. This conductor is 40 feet in length with the last 8 feet running inside the electrical cabinet of the HVAC unit. Is it possible that I am picking up noise from contactors or motor leads? I am just thinking out loud. I may have to re-route this cable. It is presently 6 inches away from the aforementioned conductors, but maybe that is too close.
Created Date: April 27,2018
Created by: RogerR
If the grounds are good and the commons are connected, then it must be something else.
Noise on the line could make the signal change or be erratic, but I don't see how it can make the signal creep up slowly over a long period of time.
The 4-20 ma signal is climbing gradually and is measurable on the plc. Maybe this is a signal generation issue instead of a measurement issue.
Can you put a substitute 10 ma signal from a device other than is being used now on one of the other inputs and see if it changes over time?
Created Date: April 27,2018
Created by: mwdkmpr
Try putting a 2400 ohm resistor in the circuit instead of the transducer. Try it at the transducer and at the PLC.
Created Date: April 28,2018
Created by: Anvilsoup
If the grounds are good and the commons are connected, then it must be something else.
Noise on the line could make the signal change or be erratic, but I don't see how it can make the signal creep up slowly over a long period of time.
The 4-20 ma signal is climbing gradually and is measurable on the plc. Maybe this is a signal generation issue instead of a measurement issue.
Can you put a substitute 10 ma signal from a device other than is being used now on one of the other inputs and see if it changes over time?
+1 to this! We have one of Vaisala's units where I work and I have found the RH sensor to be especially prone to instrument drift. Some other testing should include grounding or ungrounding the negative on your power supply. You might try swapping the known "good " unit for the "problem " unit.
Along with the substitution of a 10 ma signal the ability to measure both sides of the 4 to 20 signal is important (for comparison, if the negative reads different than the positive you will have to search why).