While in the process of setting up my temperature transmitters, I hit a wall; I don't have the ability to simulate an RTD.
There are few items available cheaply to do this. Ex:
http://cgi.ebay.com/NIB-Altek-RTD-Mo...temZ7603542207
(btw, that one is on a alpha curve that is american only. European curve is 3850)
For those wishing to catch up:
http://www.capgo.com/Resources/Tempe.../RTDs/RTD.html
The problem:
I need to simulate an RTD at the following temperatures:
-200 deg C
+850 deg C
+15 deg C
+20 deg C
+25 deg C
+30 deg C
+35 deg C
This is done by applying a precicion resistor (0.01% accurate) to the input of the temperature reader.
The values are (respectively):
18.52 Ohm
390.48 Ohm
105.85 Ohm
107.79 Ohm
109.73 Ohm
111.67 Ohm
113.61 Ohm
The existing equipment:
I have two Fluke 8840A multimeters capable of displaying 0 to 199.999 Ohms (on one range) with an accuracy of somewhere around 0.01 Ohm. I have the calibration certificate for one of them, but it expired in April last year. The certificate indicated that it was almost dead on on resistance and voltage, but on the edge for mA (at ~87% of tolerance). The mA scale is going to be useless for this though.
I have two REF192FS precision voltage references
http://www.analog.com/en/prod/0,,769_838_REF192,00.html
Good for 2.500 volts, +/- 0.002 volts. Can also be configured as a current reference.
I have a few AD7713 that could be used as a 200 uA source, if I can figure out how to turn it on, without building the complete circuit around it.
http://www.analog.com/en/prod/0,2877,AD7713,00.html
The non-existing equipment:
A bunch of precision resistors available on eBay, with 0.01% accuracy:
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=2558643929
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7604640652
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7552610442
http://cgi.ebay.com/ws/eBayISAPI.dll...tem=7602043682
(that last one isn't available anymore, but I'm hoping it'll be relisted shortly)
The question:
How do I simulate an RTD using the above?
Hint: I'm thinking about using an array of variable resistors, in parallel, to get to the specific resistances. Normally, one would use a decade resistance box, with 0.01% accuracy, or a resistance simulator of some kind. Both of these are insanely expensive, and I'm looking for a cheaper option.