troubleshooting Auber PID/RTD

[lgxg]

hi everyone. thanks in advance for the help. I'm an electric noob, but I've built a an electric rims tube/natural gas hybrid system.

i was brewing yesterday and I ran into a problem with the reading from my RTD in my RIMS tube. It was reading really high. at first only about 30 degrees high, then after connecting and reconnecting the cable it read in the 600s or 700s.

Here is what i'm using

1. Auber pid - 2352 for SSR. It is set correctly for RTD instead of thermocouple. Set with parameters from here: https://www.homebrewtalk.com/f170/auber-2352-settings-programming-instructions-305710/
reds are connected to 3/4 and white to 5 per instructions

2. Liquid tight RTD - http://www.auberins.com/index.php?main_page=product_info&cPath=20_15&products_id=246

3. RTD cable and connector - http://www.auberins.com/index.php?main_page=product_info&cPath=7_35&products_id=269

I contacted auber and the first step of trouble shooting was to put a jumper between 4 and 5 on the PID and reset Sn to 0 to set it back to thermocouple. It read at about ambient - around 70F. Does this eliminate the PID as the problem?

The second thing they had me do was to test the resistance on the RTD. I took it out of the RIMS tube. I used the continuity function on the ohmmeter to see that pins 1 and 3 are red, 2 is white. I get the beep for continuity and when i test resistance across the 2 and 1 or 2 and 3 I get resistance in the 150-180 range depending on how good of a connection I can keep with the probes. The setting on the ohmmeter i used was 200ohm.

Am I correct to assume that this rules out the RTD as a problem?

Next I tested the connector part that connects to the PID and the male connector that goes on the outside of the control box. I confirmed that there is continuity between all three pins and the leads that connect to the PID.

Am I correct to assume that this rules out the male connector and the cable that connects to the PID as the problem?

Lastly I tested the cable. I pulled back the female connectors to expose the pins and the cable that was soldered. I used the continuity function to test if there are maybe breaks in the cable or something wrong with the connector. I tested pin 2 (white) and got continuity. I then started to test pin3. when I tried pin 3 to pin 3 (both through the connector and just via the soldered joint on the inside of the connector I did NOT get the beep to signal continuity. But when I touched pin 1 to pin 3 on the other side of the cable I got the beep. This was true on both sides of the cable.

Does this mean that the cable is bad? It is a steel cable with a teflon coated white/red/red cable inside. It has definitely been rolled up and possible kinked. What type of continuity is this cable supposed to have?

Thank you all for the help. I want to make sure my thought process is right before I start ordering new stuff from Auber.

 

[Facinerous]

From everything you listed it does sound like the cable is the problem. If you have both ends disconnected then each wire should only ring out to itself but nothing else.

 

[lgxg]

I'm thinking that a kink in the cable may have rubbed off the protective sheathing inside. maybe there is a short between the two red wires inside the cable. this may be causing me to get continuity between two different pins - it's just coincidence that they're both red, maybe?

my only problem with that thought is that within the RTD pins one and 3 (red) end up getting soldered together inside the RTD. Photo of inside RTD: https://plus.google.com/10927057073...6066451593309021986&oid=109270570738526176065

I found this link to explain how RTDs work, but it's obvious my understanding is lacking. http://www.sensorsmag.com/sensors/e...tal-multimeters-quick-checks-temperature-1087

RTDs can have two, three, or four leads. In a two-wire configuration, simply connect the meter across the leads and measure the resistance. For a PT-100 RTD at room temperature, this should be about 110 Ω (±20%). If you grab the tip of the RTD, you should see the resistance increase. Let go, and you should see the resistance gradually settle back after you release the tip.

Three-wire RTDs are commonly used when a measurement system is made up of resistance bridges. The wires that connect the tip to a measuring device have a temperature-dependent resistance of their own (as do all metals). The extra wire helps the bridge balance out the effects of lead resistance. When checking a three-wire RTD with an ohmmeter, all you need to know is that two of the three wires should be shorted. Usually, the shorted wires are the same color. Between any of the shorted wires and the third wire, the transducer should act just like its two-wire counterpart. That is, at room temperature, the meter should read about 110 Ω for a PT-100 RTD, and resistance should increase slightly as the temperature at the tip increases.

 

[Facinerous]

That is a possibility, but I think it is a little different than that. I may be wrong but here is my logic.

The RTD works like this. Your PID sends a voltage out on one of the red wires out to your RTD. The RTD is just a resistor, but kind of special. Resistors value changes on temperature. So the hotter something gets the higher the resistance will be. The white wire sends a return voltage back at a reduced voltage from the RTD and your PID can calculate the temperature. The second red wire works just like the white wire, but sends a second voltage back that tells the PID the resistance of the wire alone.

Since your PID was reading voltages lower than they should have been, (I assume) basically one of the wires between the reds and white was getting very close to becoming broken. The bad connection increased the resistance in the wire and gave your PID a bad reading to go by. When you disconnected and reconnected the connection a couple times this actually broke the wire enough to where your PID was seeing the highest resistance it could see and translated that into a ridiculous temperature.

If the wires were shorted together then your PID would have an insanely low temperature.

 

[Ozarks Mountain Brewery]

these stainless cables from auberins can kink and short out, I went trough several before I added a nylon sleeve to my cables. its not easy to re solder the ends but its worth it to keep the readings correct

 

[lgxg]

that makes total sense. one of the wires inside the braided steel and teflon sheath is probably broken. likely one or both of the red wires. that would explain why i'm not getting continuity on wire 3. still not sure why i'm getting continuity when i test across pin 1 and 3.

does the thermocouple test that auber had me do completely rule out the PID from the equation? how about the continuity test for the male connector that's used to connect the female/female cable - does that rule out that piece?

thanks so much for your thoughts on this. i'm an accountant that's quickly learning more and more about electronics.

 

[raysmithtx]

I had a similar problem and traced it to a cold solder joint in the connector. See the thread I started, "troubleshooting advice needed". I'm on a ipad and can't post the link. It drove me crazy for a while but once I resoldered the connectors I have had no problems since.


Sent from my iPad using Home Brew

 

[Facinerous]

As far as your actual RTD is concerned I would say you are 90% safe to rule that out. I'm only gonna say 90% because I don't know how dramatic the resistance would change in varying temperatures.

That PT-100 should be 100 ohms from the red to white at 0 degrees C. So your measurement of 150-180 at ambient or I'm assuming 20 degrees C is very likely correct.

 

[lgxg]

one other quick question - is there any reason why i couldn't reuse the connectors and make my own cable?

Here is a picture of the connectors connected to the current cable:



it's pretty low gauge wire. seems like something just smaller than 18 gauge.

 

[Facinerous]

There is no reason at all that I can think of. I say go for it. Connectors can be a PITA, but it sounds like you have a good understanding of what is going on.

I will say you should make sure the problem is truly the wire, and not the connector or the connections at the connectors. I'd hate to see you buy new wire when all you needed to do is resolder a connection.

For some reason your photo link isn't working for me.

 

[lgxg]

i found your thread here: https://www.homebrewtalk.com/f170/fluctuating-temps-troubleshooting-advice-needed-487132/

this is very similar behavior that I saw at first.

I had a similar problem and traced it to a cold solder joint in the connector. See the thread I started, "troubleshooting advice needed". I'm on a ipad and can't post the link. It drove me crazy for a while but once I resoldered the connectors I have had no problems since.


Sent from my iPad using Home Brew

 

[lgxg]

i fixed the photo in the previous post.

i'm new to soldering. i'm thinking i'll just buy a new cable. after reading ray's issues i'll double check the new cable and maybe add a little solder to it.

thank you all for the help.

 

[lgxg]

these stainless cables from auberins can kink and short out, I went trough several before I added a nylon sleeve to my cables. its not easy to re solder the ends but its worth it to keep the readings correct

that's a really good idea. how did you add the nylon sleeve? I googled, but could find a tutorial.

did you just put it over the SS braided cable or did you use one of their regular cables and put a sleeve on that?

 

[Ozarks Mountain Brewery]

the only way to be sure its the wire or not is to use another, I always buy 2 of everything for that reason, the Teflon wires with a nylon sleeve will not kink by the way

 

[lgxg]

ok. i think i'll buy one of these and put a cable sleeve on it. this would bypass the male connection as well.

looks like here is a cable sleeving tutorial: [ame]https://www.youtube.com/watch?v=WNA2pkcrSMc[/ame]

the only way to be sure its the wire or not is to use another, I always buy 2 of everything for that reason, the Teflon wires with a nylon sleeve will not kink by the way

 

[augiedoggy]

I am in the process of switching over from the stainless sleeved cables to these teflon ones with the quick disconnects rtd's... already had one of the stainles ones fail at the sensor base...

http://www.ebay.com/itm/380938165742?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT
Just received these today... very impressed with the quality so far.

 

[lgxg]

I am in the process of switching over from the stainless sleeved cables to these teflon ones with the quick disconnects rtd's... already had one of the stainles ones fail at the sensor base...

http://www.ebay.com/itm/380938165742?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Those are a good deal.

 

[lgxg]

I am in the process of switching over from the stainless sleeved cables to these teflon ones with the quick disconnects rtd's... already had one of the stainles ones fail at the sensor base...

http://www.ebay.com/itm/380938165742?_trksid=p2059210.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Those are a good deal.

 

[Ozarks Mountain Brewery]

you can get different material and sizes from different places

http://www.amazon.com/gp/product/B004GE49US/?tag=skimlinks_replacement-20

http://www.ebrewsupply.com/fray-resistant-braided-sleeving.html?SID=b8fded0986d59dfdd0e5416326f4a86e

http://www.theelectricbrewery.com/custom-temperature-probes

most of the time they expand twice their size to so order small

 

[lgxg]

here's someone that did it for their cables. looks nice.

http://rottensebrewery.blogspot.com/2013/06/temperature-probes.html

 

[orangehero]

That wire rope in the sheath is absolutely unnecessary. If something happens I would rather the wire break than have damage to the connectors, temp probe, or panel. Wire is cheap to replace or resolder.