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  1. #1
    Join Date
    Jun 2011
    Posts
    18

    TAC 7716 Tekmar compatability

    I am trying to take over the snowment system for a hotel. I am using a TAC/ Schnieder Electric 7716 control board to do the work. Currently they are using a Tekmar snow melt system. Everything seems to cross over ok except the moisture sensor. They are using a Tekmar 090 snow/ice sensor. This sensor has a 10k ohm slab temp sensor, a 10k heater element temp sensor and a 2,000,000 ohm moisture sensor. The 2 temp sensors work nicely with my controller as I can configure the input to accept a 10k ohm RTD style sensor. However the moisture sensor is making me scratch my head. When it senses moisture it goes from 2,000,000 ohms (dry condition) to a range of 10,000 to 300,000 ohms(wet condition). Any ideas on how I can get this down into a more manageable range? Or should I abandon ship on the moisture sensor and install a separate dry contact style of moisture sensor?

  2. #2
    Join Date
    Jul 2012
    Location
    Northern NY
    Posts
    121
    If you are just looking for making this a binary style logic and don't care about the actual level of resistance you could either user a voltage divider using an equal resistance to turn this into a voltage signal. Most panels put out some sort of voltage to read resistance so this would be your input voltage, then your sensor would be R1 and a know resistor (good sized resitance would be better) would be r2 and you could see either 1 of 2 voltages and use this to determine if you have moisture or not.

    http://www.raltron.com/cust/tools/voltage_divider.asp

    Another option is to place a resistor in parallel with your sensor to get the resistance down to a range you like. Your sensor would be R1 and another resistor (around 10K ohms) would be R2, this would give you about 9950 ohms at dry to 9677 to 5000 ohms when wet which maybe in a more readable range for your panel.

    http://www.sengpielaudio.com/calculator-paralresist.htm

    You could switch the sensor but they are expensive and resistors are cheap.

    -Jeremy

  3. #3
    Join Date
    Dec 2006
    Location
    Hartford, Connecticut
    Posts
    442
    Are there any lookup tables on those input points? Also is the range and counts (resolution) setup?

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