[Hai-users] Temp sensors accuracy again.

Sat Jan 14 10:16:08 CST 2006

In our commercial application we were looking for 1/10 degree temperature control for two reasons that I can recall.

First, we were controlling temperature in commercial buildings. There were some tenant complaints, often caused by issues outside of our control. Stuff like excess radiant heat when the sun shone through the windows, or oversized units, poor air balance, etc. When tenants complained about comfort issues they sometimes would threaten the landlord to withhold rent payment because their contract said something about the landlord keeping the property comfortable. Tenants would often bring in their own thermometers to track temperature. If there was a difference we had to go in and prove our sensors were accurate to remove ourselves from the conflict. So we had a NIST traceable thermometer we used as a temperature reference. Plus or minus 3 degrees was not good enough to win this argument.

Second, when installing systems with hundreds of sensors the labor to field calibrate each and every one was huge. So it was much better to connect and forget.

In the home, +/- 5% accuracy is more of a nuisance. If you have only one humidity sensor it's probably not noticeable, but if you have several and they read different it bugs you. It's like having every clock in the house reading a five minutes different. You begin to question the quality of the system. But 35-40% errors are nuts.

----- Original Message ----- 
  From: Brett Griffin 
  To: 'Ken Schumm' 
  Cc: hai-users at tssi.com 
  Sent: Friday, January 13, 2006 10:45 PM
  Subject: RE: [Hai-users] Temp sensors accuracy again.

  Ok, so I have read this conversation many times over the years, and have heard different explanations.  I have some questions, please take a moment to read and don't get annoyed that I take a defensive stance, I am really trying to create a good dialogue, and maybe HAI will read this and make adjustments.

  My few questions, What is everyone doing with these temperature sensors that you need .1% accuracy?  You cannot program the HAI system to respond to decimal levels.  So your programs have a 1 degree accuracy, and realistically thinking a 2 degree accuracy since you cannot and should not write a two direction program with the temps setting closer than 2 degrees.

  I have an OP2, and I had about 4 temp and humidity sensors hooked up to the system prior to my move to my new residence.  I used them for outside temp, and curious things like the temp inside my controller, my basement, and my second floor.  I could care less if the temp outside was 14 degrees or 18 degrees, regardless I had to dress warm.

  Not I understand that there are some more critical things like humidors and wine cellars, but even the accuracy is not going to make a overall difference.

  The point of the temperature sensor being next to the thermostat, I can understand the frustration that they are off by a couple of degrees.  However taking the safe assumption that the error likely tracks over the temperature range (i.e. your home temps swing about 25 degrees for extremes) why not just adjust the thermostats to match the temp sensor.

  The same being true for humidity. What are you guys doing that requires such high accuracy in your home?  The application I have run are like turning the bathroom fan on while taking a shower.  The humidity will climb close to 100% so I write rules that if it exceeds 70% turn the fan on.  If you have an air conditioned home, your humidity levels will swing between 30-45%  Much beyond those levels you got problems like static electricity build up and mold.  Again I don't see an application that requires such high accuracy.

  Now I understand the concerns of what's expected and what's reflected are not the same thing and that is a legitimate complaint.

  Now to my next question, I am done Ranting, now I am pondering...

  If you could buy a $20 radio shack sensor and make it work with the HAI system, would you buy them over the $80 temp sensor?  What if the accuracy was +/- 2 degrees.  Would you buy one for general use like I do, and buy the higher accuracy ones for humidors and wine cellars, where the accuracy was more critical?

  Just trying to get insight to your concerns, and by now means do I intend to derate your complaints.

  Brett Griffin
  Architechtronics
  www.architechtronics.com

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    From: Brad [mailto:looney2ns at sigecom.net] 
    Sent: Friday, January 13, 2006 5:46 PM
    To: 'Ken Schumm'
    Cc: hai-users at tssi.com
    Subject: RE: [Hai-users] Temp sensors accuracy again.

    Thanks for the replies Ken. Your explanation makes lots of sense. Hadn't thought of the wire length issue.

    I'm comparing the readings to a $300 Kestrel 4100 Pocket HVAC tool.
    Its temp specs are +/- 1.8 degrees.
    Humidity specs are +/-  3%

    I also have 3 of the Radio Shack gauges, and those and the Kestrel agrees with each other within a few tenths of each other on temp and Humidity.

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    From: hai-users-bounces at tssi.com [mailto:hai-users-bounces at tssi.com] On Behalf Of Ken Schumm
    Sent: Friday, January 13, 2006 4:59 PM
    To: Brad
    Cc: hai-users at tssi.com
    Subject: Re: [Hai-users] Temp sensors accuracy again.

    Just curious, if your humidity readings are off what are you comparing them to? I believe the Radio Shack humidity sensor is accurate to +/- 5 %. If the HAI is also +/- 5% the difference between the two could be 10% and they'd be within specs.

      ----- Original Message ----- 

      From: Brad 

      To: 'Wenzel, Guy' 

      Cc: hai-users at tssi.com 

      Sent: Friday, January 13, 2006 2:00 PM

      Subject: RE: [Hai-users] Temp sensors accuracy again.

      In my case, the thermostats readings are very accurate; it is the Temp.Humid sensor's that are off.

      The new temp/humid sensors can not be calibrated. The Thermostats can be if needed.

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      From: Wenzel, Guy [mailto:Guy.Wenzel at capella.edu] 
      Sent: Friday, January 13, 2006 12:40 PM
      To: Brad
      Cc: hai-users at tssi.com
      Subject: RE: [Hai-users] Temp sensors accuracy again.

      I have a similar setup with an Omnistat and a Temp sensor in the hallway near the same room and see the same 3 - 5 degree difference.  I have not cheeked to see which is more correct.  Does anyone else know if it can be adjusted or just the thermostat?

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      From: hai-users-bounces at tssi.com [mailto:hai-users-bounces at tssi.com] On Behalf Of Brad
      Sent: Friday, January 13, 2006 12:19 PM
      To: hai-users at tssi.com
      Subject: [Hai-users] Temp sensors accuracy again.

       Just installed 3 HAI temp/humidity sensors. Also installed 3 HAI OmniStats with remote temp sensors. The Thermostat remote sensors and the Temp/Humidity sensors are mounted on inside walls within 6 inches of each other, each set in a different room. Temp/Humidity sensors show temps being 3-5 degrees higher than the thermostats show.

      Apparently HAI STILL has not resolved the issue of the Temp/Humid sensor's being inaccurate.

      The Humidity is reading low on them as well. Very frustrating.

      Anyone else seeing this?

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