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High temperature readings via J4CN1 analog cards Messages in this topic - RSS

JHBrown
JHBrown
Posts: 8

1/16/2019
One of our buildings has several FC5A Web Server CPU modules, each fitted with multiple J4CN1 analog cards.
It was intended to use four of these to acquire temperature data at multiple points within the exterior wall assembly.
Upon digging in:
The first challenge is to understand why 8 type K thermocouples were all reading higher than actual conditions, eg. The wall exterior should be 60 deg. F, the sensor reads 125 deg. F.
Since this could be mired in the CVDT(W) S1 – D1 and DIV(F) S1 – D1 with S2 value adjustment, I put that aside to do a simple test.
Each thermocouple was detached from the analog card(s) and tested (in place in the wall) with a Fluke capable of type K temperature readings.
The results were as anticipated for the wall assembly given the outdoor and indoor temperatures.
The sensors were reconnected to the cards and the PLC was run , program was re-started.
As observed, the starting readings were closer to the expected wall temperatures, but after a brief time they rose to an unexpected not realistic temperature.
After seeing this, I pulled the power supply, the CPU and the cards out of the 9”x9”x9” hoffman metal enclosure and bench tested the assembly.
The “bench test” was done in a well ventilated room at 78 deg. F.
Only two type K thermocouples were connected to card 1.
The program ran for a couple of hours and the thermocouples were responsive to temperature changes.
Both ran a bit higher than expected but by only a few degrees, e.g. 82 deg. F. (I used a Fluke temperature/humidity digitial to confirm).
After seeing this I started to suspect that the small enclosures used to house the power supply, CPU and cards may be the root of our erroneous temperature problems.
At this location, the metal enclosure is typically closed, and is located in a cabinet within the room. These enclosures are not ventilated.
Question:
1) Because of the physical nature of a thermocouple using a “hot junction and a cold junction” , is the “cold junction” effected by the heat accumulation within the enclosure and proximity to the CPU and power supply.??
2) Are there good documents or examples of transmitting the acquired temperature data over the internet such that a remote user can use
te the results (such at the HTML mentioned below). I have some knowledge of HTML.

Attachments:
IMG_4144.JPG
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JHBrown
JHBrown
Posts: 8

17 days ago
JHBrown wrote:
One of our buildings has several FC5A Web Server CPU modules, each fitted with multiple J4CN1 analog cards.
It was intended to use four of these to acquire temperature data at multiple points within the exterior wall assembly.
Upon digging in:
The first challenge is to understand why 8 type K thermocouples were all reading higher than actual conditions, eg. The wall exterior should be 60 deg. F, the sensor reads 125 deg. F.
Since this could be mired in the CVDT(W) S1 – D1 and DIV(F) S1 – D1 with S2 value adjustment, I put that aside to do a simple test.
Each thermocouple was detached from the analog card(s) and tested (in place in the wall) with a Fluke capable of type K temperature readings.
The results were as anticipated for the wall assembly given the outdoor and indoor temperatures.
The sensors were reconnected to the cards and the PLC was run , program was re-started.
As observed, the starting readings were closer to the expected wall temperatures, but after a brief time they rose to an unexpected not realistic temperature.
After seeing this, I pulled the power supply, the CPU and the cards out of the 9”x9”x9” hoffman metal enclosure and bench tested the assembly.
The “bench test” was done in a well ventilated room at 78 deg. F.
Only two type K thermocouples were connected to card 1.
The program ran for a couple of hours and the thermocouples were responsive to temperature changes.
Both ran a bit higher than expected but by only a few degrees, e.g. 82 deg. F. (I used a Fluke temperature/humidity digitial to confirm).
After seeing this I started to suspect that the small enclosures used to house the power supply, CPU and cards may be the root of our erroneous temperature problems.
At this location, the metal enclosure is typically closed, and is located in a cabinet within the room. These enclosures are not ventilated.
Question:
1) Because of the physical nature of a thermocouple using a “hot junction and a cold junction” , is the “cold junction” effected by the heat accumulation within the enclosure and proximity to the CPU and power supply.??
2) Are there good documents or examples of transmitting the acquired temperature data over the internet such that a remote user can use
te the results (such at the HTML mentioned below). I have some knowledge of HTML.
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JHBrown
JHBrown
Posts: 8

17 days ago
I'm still fighting this challenge and not getting anywhere. How do I go about determining if this is a hardware or software problem?
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DaDaDadeo
DaDaDadeo
Posts: 70

15 days ago
Try using a transmitter. The PR Electronics 3101 may work out well. It has dip-switches that can be set with no software. We use the 3112 transmitter for 4 wire RTDs to the J4CN1.
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Mark Paulus
Mark Paulus
Posts: 23

10 days ago
I have seen grounding issues before. The thermocouples and plc worked fine on the bench. Installed in the machine and the temp values in the plc were reading erratically. Figured out that when we touched (grounded) the thermocouples to the frame of the machine the plc didn't like it. We saw erratic numbers. Took the mechanical clamp off the thermocouple and it stabilized. We had thermocouples with "grounded" junctions. Essentially the two wires are internally bonded to the metal tip of the T/C. This would not have been an issue if we had ordered the "ungrounded" junction version. Just a thought...
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JHBrown
JHBrown
Posts: 8

10 days ago
I think there is some agreement here. A series of tests this morning (with our local IDEC representative) confirmed "ungrounded" type K thermocouple readings to be credible and stable. The existing embedded hand tied type T thermocouples would in fact all be grounded to certain degrees as some are embedded within foam insulation, some attached within foil barriers and at least one touching external metal building skin.
This may end up as a lessons learned for others..... However, I need to now come up with a solution for the 40 embedded and grounded type T thermocouples, the five IDEC PLC's and the 10 to 14 J4CN1 cards that I have.
edited by JHBrown on 2/11/2019
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JHBrown
JHBrown
Posts: 8

10 days ago
DaDaDadeo wrote:
Try using a transmitter. The PR Electronics 3101 may work out well. It has dip-switches that can be set with no software. We use the 3112 transmitter for 4 wire RTDs to the J4CN1.

Thank you for the advice. Please see the next few discussions on this thread relating to the possible cause of unacceptable readings. If there was a way to test out the product to see if it were more tolerant of the possible "grounding" issue, I would give it a go. Is there anyway of obtaining one card for testing purposes, whereby if it solved an otherwise expensive problem, I would want to purchase enough for 40 sensors.?.
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mc
mc
Posts: 9

9 days ago
I have had a similar issue in the past. I used a transmitter as DaDaDadeo suggested and that solved the issue in my case. I set a transmitter centered to where the thermocouples were physically located then ran the 4-20ma analog outputs to the FC6A-J4CN1 card. Here is a link to the transmitter and programming keypad for the transmitter https://www.omega.com/pptst/TXDIN70.html
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JHBrown
JHBrown
Posts: 8

8 days ago
Thanks for the link. The Manufacturer suggests ungrounded thermocouples to be used with their card. Our installation, see the attached picture, uses simple hand twisted thermocouples installed into our building walls at time of construction. There are several type T or J installed where by it is likely that any of them are "grounded" at the hot junction. While some are in insulation foam (insulated likely from ground), others may be touching foil facing or building surface metals. See https://blog.wika.us/products/temperature-products/faqs-thermocouple-selection-grounded-vs-ungrounded/ for a good article the subject. Our PLC's are installed in small hoffman enclosures that left no room for additional cards. If the Omega product could solve the hardware problem, I would need to rework 5 stations such as the attached file Room 421, by adding sufficient cards to accept 8 to 10 sensors.
Oddly enough, the fluke that was to test some of the embeded sensors did not seem to be effected by what may be a "grounding" problem (or perceived that way), credible temperature readings resulted using the type K input capability on the Fluke.

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mc
mc
Posts: 9

7 days ago
Were there any provisions made in building design/construction for accessing the thermocouples if there was ever a need to replace one?
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JHBrown
JHBrown
Posts: 8

7 days ago
No provisions for accessing the installed sensors, however, a completely redundant parallel set were installed and have not been used. One thing mentioned in a prior post, was that of using a hand held Fluke to test the installed sensors. That unit came with a type K un-grounded sensor, which may have circuitry to compensate for the different types. Obviously, I'm trying to make sense of it all in an attempt to quickly get to a workable (or work around) solution.
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mc
mc
Posts: 9

7 days ago
My first suggestion if you were able to access the TC's would be to install thin walled non-adhesive heat shrink over the tie points. this will slow down the response time of the joint to pick up temperature shift but in your application I do not think it would be apparent. This should eliminate the known grounding issue.

Is it possible the fluctuation in reading is caused by ground potential difference between the points where the TC is grounded and the connection at the PLC? If this is the case or a major contributor you could try connecting the 0 vdc of your power supply output to ground at the power supply 0 vdc terminal. If the bonding and grounding throughout the building is correct that should bring the possible ground potential down and may help reduce the fluctuations. This is if the analog card can handle a grounded sensor at all.


Outside of that I think you are down to checking to discern which TC's are grounded and which are not and only connect the ones not grounded directly to your PLC. Then either find a transmitter that can handle a grounded TC or replace those particular TC's with an ungrounded TC. It looks like from the wall mockup you could add new relatively easily and inexpensively. Of course if you do not have drop ceiling or some type of adequate ceiling access that may not be feasible either.

This is a good reference info for TC also. http://www.instrumentationtoday.com/thermocouple/2011/08/
edited by mc on 2/14/2019
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