AD592 Temperature Sensor Resolution

smattstone

Hi All!

I am new to the forum and to the Basic Stamp.· I would like to request some help.· I am building a water temperature sensor using the BS2 and a AD592 temperature probe.· I have a program written that reads the probe and reports the temperatue in degrees K and C.· The problem is I need the reported temperature to resolve to .1 degree.· I used the rctime command.· The section in the applied sensors book indicates that the codes rounds the output to the nearest degree.· Is ther away to get around this rouning function or at least alter it to round to another significant digit.· Your assistance is appreciated.

Tracy Allen

The RCTIME command is not stable enough for 0.1°C accuracy. You will need a 12 bit ADC such as the MCP3202 with a 4.096 Volt supply/reference. Terminate the current with a 10kΩ resistor, so 1µA/°C becomes 10mV/°C at the input to the ADC and then the resolution will be 1 mV = 0.1°C.

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Tracy Allen
www.emesystems.com

smattstone

Tracy:

Thanks for the response.· I have serched but can't come up with a schematic or source code to operate the adc.· I may be over-complicating.· Can you assist?· Greatly apreciated.

Steven

Franklin

Have you tried here? www.parallax.com/StoreSearchResults/tabid/768/txtSearch/mcp3202/List/0/SortField/4/ProductID/575/Default.aspx

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- Stephen

smattstone

I'm looking at that now. I don't quite understand it. I'll try to muddle through it. Thanks

smattstone

Okay Guys -- I admit I need some more help. I think I've missed something here. I using a AD592 temp probe and added a MCP3202 ADC with a 10K ohm resistor trying to obtain temperatures resolving to .10 degrees c. here is what I've done thusfar.

Using a BS2 / Board of Education / AD592 / MCP3202 / MCP3202 sample code / all connected as follows

BS2 Pin 0 to 3202.1 CS/SHDN
1 to 3202.7 Clock
2 to 3202.6 Dout
3 to 3202.5 Din

Vdd to 3202.8 Vref
Vss to 3202.4 Common

AD592 + (red) to Vdd
AD592 to 10Kohm to 3202.2 Channel 0

Any assistance is appreciated

Franklin

What do you get when you run the code? The - lead of the ad592 should go to the 3202 pin and through a ~1k resistor to ground. take a look here www.analog.com/static/imported-files/data_sheets/AD592.pdf

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- Stephen

smattstone

Using the 10k resistor the debug screen displays the following.

ADC CH0 2106
Volts 2.574

I am trying to create a temperature sensing program that resolves to the tenth of one degree celsius. Therefore converting the 1uA/1K current output of the AD592 to 10mV/1K so 1 mV = .1K. I believe I have missed something.

Tracy Allen

Oh, you should connect the AD592 + lead to Vin not to Vdd. The AD592 needs more than 2.5 Volts across it in order to operate correctly.

With 5 volt reference for the MCP3202, you will need a 12.2 kΩ resistor in order to achieve 0.1 degree resolution. That could be a 12k 1% resistor in series with a 500Ω pot, or something equivalent to set the calibration.

12207 Ω * 0.1 E-6  A = 0.0012207 V

That is the resolution of the converter with a 5 Volt supply, 1.2207 mV per bit, and 0.1 µA is the sensor change in current for 0.1°C change in temperature.

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Tracy Allen
www.emesystems.com

sam_sam_sam

I did the same thing how ever I used a MAX186

I use the code bellow and works very well

 DO

  PAUSE 5
  LOW CS                                          ' Enable ADC
  SHIFTOUT DataIn, Clock, MSBFIRST, [noparse][[/noparse]%10111101]   ' Select CH6, Single-Ended [noparse][[/noparse]%1XXX1101]
  SHIFTIN DataOut, Clock, MSBPOST, [noparse][[/noparse]KLN\12]       ' Read ADC
  HIGH CS                                         ' Disable ADC

  [color=red]tf = KLN  - 273 * 9 / 5 + 32  ' convert to tenths F[/color]

  SEROUT TX, T2400, [noparse][[/noparse]LcdLine1,"T_F ",  DEC  TC]   ' Displays voltages & digital value

  LOW CS                                          ' Enable ADC
  SHIFTOUT DataIn, Clock, MSBFIRST, [noparse][[/noparse]%11111101]   ' Select CH7, Single-Ended
  SHIFTIN DataOut, Clock, MSBPOST, [noparse][[/noparse]KLN1\12]      ' Read ADC
  HIGH CS                                         ' Disable ADC

 [color=red] tC = KLN1 - 274 ' convert to tenths C[/color]
 
  SEROUT TX, T2400, [noparse][[/noparse]LcdBLon, LcdLine1_1,"T_C ",  DEC  TC]  '

I hope this helps

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·Now wanting to learn Spin· Thanks for any··that you may have and all of your time finding them

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Sam

Post Edited (sam_sam_sam) : 6/28/2010 11:31:43 AM GMT