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Tekmar Slab Sensor

I'm running about 4,000 square feet of driveway snow melt with a Tekmar 667 controller.  I'm using an 073 slab sensor to monitor the slab temperature.  This is the third season in use, and it's running great except this year I'm getting a bogus reading for slab temperature.  I'm reading regularly between 88 and 95 degrees F, which I know is not reality.  I've been able to limp through the year keeping the system idling and by setting the idle temperature I'm able to regulate the supply temperature feeding the slab, thereby keeping everything melted nicely.  Has anyone had an issue like this?  If it's just a bad sensor that's a simple enough fix, but they're not cheap so I don't want to buy another one just to troubleshoot.  Any insight is appreciated.  Thanks!

Comments

  • MJS
    MJS Member Posts: 18
    Tekmar makes a

    10K Temperature Simulator 002 for around $270. It's a way to see if it's the control or the sensor that is faulty.
  • Ironman
    Ironman Member Posts: 6,703
    Wrong sensor?

    You're using the wrong sensor. The 667 requires an 090 slab sensor. The problem is that the 090 requires an 091 brass socket which is embedded in the slab.



    The 073 is a 10k ohm thermistor. It should read 10k ohms @ 77deg.



    You can find all the info you need on Tekmar's web site or call their tech support.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Randy Baerg
    Randy Baerg Member Posts: 26
    073 sensor reading too high

    The 667 can use a slab sensor for system not requiring automatic start.

    one possible issue with slab temperature reading too high would be that the sensor is located too close to a supply pipe. Can you push or pull the sensor into a spot that is not as close to the piping?

    Another possible cause is that the sensor has become infiltrated with water which reduces the resistance, leading to temp reading too high.

    Often you will see that the conduit that the sensor is inserted into is filled with water. That is not good. You should make sure the slab is warm and blow out the conduit with compressed air. Then seal it or extend it so it can not fill up with melt water.

    If the sensor is water damaged then you will need to replace it with a new 072 or 073.

    You should be sure to get the newer version of the sensor (Manufactured after June 2010). These sensors have been changed to an over-molded design which provides much better water resistance. They are also a little smaller so they are easier to fish into your conduit.

    Here is a link to the new sensors: http://tekmarcontrols.com/media/literature/072_d_06.pdf
  • Big Ed_4
    Big Ed_4 Member Posts: 1,829
    edited March 2011
    Sensors Go Bad

    They can go bad... For the fact you notice a difference from years before where it worked fine , After checking the program for any change, You would want to check the sensor next. But as stated , reading the resistance of the sensor and comparing the temperature of the slab would be the test... A temperature / ohm chart would be needed .W ater is the biggest culprit of sensors gone bad :) What was the sensor inserted in ? Always best to cap the end of the insertion tube and seal the access port .... If you notice any water if you pull it out, dry the tube out somehow before installing a new one . If your unsure if it's capped or not a vacuum test will tell .
    I have enough experience to know , that I dont know it all
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