Compatible RTD temp probes

[corley]

I'm needing some help finding an RTD, ICTD, thermocouple or whatever that works well with the TMD-100. I've tried using a 10k thermistor but the voltage return range was only 2.48 to 3.78 vdc. This is not a good enough range to provide me with an accurate temperature reading. It appears to use these types of sensors that I would need a transmittor or amplifier. I don't want to spend that much money tho. Has anyone here found a temperature probe that works well that doesn't require these things to work?

[Orlando]

Please check out our analog modules. We have a board ETRTD which accepts 4 RTD Pt1000. It provides 0-5VDC analog output voltages which can be directly connect to the AD port of the T100.
More info in www.lt-automation.com

[Fernandz]

Have you looked into an IC sensor. I have played around with the LM335 and had some good results.

[corley]

Thanks alot Orlando.. I think this would be ok solution... although I'd love to see a standard sensor without a transmitor work directly with this plc.  I'm going to play around and create an opAmp and see how it turns out too.

Please check out our analog modules. We have a board ETRTD which accepts 4 RTD Pt1000. It provides 0-5VDC analog output voltages which can be directly connect to the AD port of the T100.
More info in www.lt-automation.com

[corley]

Thanks for the reply.. I've not played with that one yet.. but I found some information today on the web about it.. Although I still wasn't sure if it would work. Were you able to directly connect this sensor without any signal conditioning, etc.?

Have you looked into an IC sensor. I have played around with the LM335 and had some good results.

[Fernandz]

http://web.mit.edu/rec/www/workshop/lm335.html   This website provided some good info including a wiring diagram. The only thing you need is a voltage divider. I need to find my notes on this but i believe the equation to read the Analog input was......
                                     
  Temp=(ADC(1)-2236)*(500)/4096     for 12bit
 
The Analog inputs are 10 bit normalized to 12 bit ....The 10 bit formula would be........................

 Temp=(ADC(1)-559)*(500)/1024      for 10bit

The LM335 puts out 10mv/DEG. K   (273 Deg K) =( 0 Deg C) =( 2.73v )=(2236 converter count @ 12 bit)...... You may have to tinker with this but i believe this is how i did it. Keep in mind that the LM335 outputs Deg.Kelvin They also make a LM35 that outputs Deg.C @10mv. Ive yet to pick one up. Plus the 5 Volts from the PLC is perfect for these IC sensors.

[corley]

I'm assuming by voltage divider you mean equation right?

Do you know if this sensor would output the full range of 0 to 5vdc? I've tried an ic type sensor before, unfortunately for me the range was 243 to 373 only. With a resistor in the circuit to convert it to 2.43 to 3.73 vdc the range was not good enough to get closer than 6-10 degrees. Also the reaction time was horrible.  I'd like to see your notes and also hear your findings on how accurate this setup was for you. The mit website, I had actually seen this too. I think they say it's accurate withing +/- 3?C which is probably ok if the reaction time isn't too slow. What did you find with that part?

Thanks alot for your help!

http://web.mit.edu/rec/www/workshop/lm335.html   This website provided some good info including a wiring diagram. The only thing you need is a voltage divider. I need to find my notes on this but i believe the equation to read the Analog input was......
                                     
  Temp=(ADC(1)-2236)*(500)/4096     for 12bit
 
The Analog inputs are 10 bit normalized to 12 bit ....The 10 bit formula would be........................

 Temp=(ADC(1)-559)*(500)/1024      for 10bit

The LM335 puts out 10mv/DEG. K   (273 Deg K) =( 0 Deg C) =( 2.73v )=(2236 converter count @ 12 bit)...... You may have to tinker with this but i believe this is how i did it. Keep in mind that the LM335 outputs Deg.Kelvin They also make a LM35 that outputs Deg.C @10mv. Ive yet to pick one up. Plus the 5 Volts from the PLC is perfect for these IC sensors.

[Fernandz]

Well no luck finding my notes but I got an interesting sensor in the mail the other day. I ordered an analog wall sensor that outputs a direct proportional reading in Deg F to voltage......So 75 'F = .75 volts. This sensor outputs .010v/'F ...........Hmmmm sounds like an LM34 sensor. The sensor and spec's can be viewed here. ATP1000  www.automated1.com  This sensor has an output of 32Deg F to 200DegF. I hooked it up to my T100MD 888 and found it to work flawless. The exact formula I am using is .

T=168*(ADC(n)-261)/1376+32          

or to display it on the LCD use:

setlcd 0,1, "Temp. =" + str$(168*(ADC(n)-261)/1376+32 )

of course keep in mind that the "n" in ADC(n) must be replaced with the correct Analog Input  1 to 8.          

[PDirac]

Hi Corley,

You might try application info. page 16 of the LT1168 from Linear Technologies. It will cost you around $10.00 and will work quite well.

PDirac