A bump, because I'm heavily into calibrating my temp transmitters.
The unit:
Moore Industries Temperature transmitter
model RIY/PRG/4-20MA/12-24DC
Specifications
Manual
(great little DIN rail mounted units, I got three, and there are still some available on eBay).
These can be configured for a single RTD (2, 3 or 4 wire) or differential RTD (3 and 2 wires, or 2 and 2 wire).
The LCD display is useless, for my purposes (only shows whole numbers). The output is a 4-20 mA, through the power supply line.
The calibration procedure calls for a "250 ohm precicion resistor, 0.01%" and a decade resistance box, also 0.01%. I'll be trying to replace the box with only the precision resistors that are needed, if I can. As for the 250 ohm resistor, I figure that it only needs to be a known resistor, and doesn't actually need to be of 250 ohm (but should be at least that much).
The resistance values for an RTD are listed here:
http://www.omega.com/temperature/Z/pdf/z252-254.pdf
(NOTE: these are for a 100 Ohm RTD, with an alpha curve of 0.003850, aka European curve)
The units are set at the "zero" and "span" points (i.e. 0% and 100% of full scale). the settings are eeprom'ed.
I'll try to contact the manufacturer, to get a copy of the linearization curve report.
For reference, all three units are set as follows:
Zero: -185
Span: 131
(I have no idea what these numbers represent)
Input: 100 Ohm RTD, alpha 385, range -200 to 850 deg C, accuracy +/- 0.05% of span, +/- 0.20 deg C
I've been going over Groth's frying pan method.
I expect I'll be putting my Fluke 8840As to work, along with the voltage reference chips.