EC150 calibrations

On 19-20 Feb, did "field check" calibrations on our 2 EC150s and the loaner IRGAson from Campbell.  (Our third EC150 is at Campbell for repair.)  For all 3, I performed the following steps:

1. Started by cleaning all lenses with isopropyl alcohol.
2. Supplied Nitrogen to the sample cell at 0.3lpm (what Andy's small cylinder produces), let settle, then clicked on "zero" using ECmon.
3. Supplied CO2 mixture to the sample cell, setting the flow rate also to 0.3lpm.  The bottle Andy gave me was labeled 396.  Read the value after settling, then clicked "span".  Checked that value was now 396.
4. Supplied H2O mixture to the sample cell from the humidity generator with a setting of 70%RH.  I didn't control the flow rate, which was larger than 0.5lpm.  (Also set the temperature set-point to 25C, but this appears not to work.)  Read both T and RH values after settling, and entered these values into a WWW-based dewpoint calculator.  Entered the resulting dewpoint into ECmon and clicked on "span".  Checked that value was now correct.

I also looked at values at 35% RH, just for sanity checking, but wasn't consistent about doing this before or after the dewpoint span.

For future reference, I'll note that the EC150 calibration cell takes 1/4" swage, the nitrogen regulator just has tygon tubing, the CO2 regulator has 1/8" swage, and the humidity generator has large hose barbs.  I made a hose to 1/4" swage fitting for the N2 and largish tubing from the humidity generator and used a 1/8-to-1/4 fitting for the CO2.  The flow gauge used 1/4" swage.  During the humidity calibration, I connected the return flow just by slipping the two tubing pieces together; during the other calibrations it was open.

Notes:

• The IRGAson behaved great.
• 1277 drifted more than usual during the calibration.  I went through the process anyway.  We should replace the scrubber chemicals.
• Before doing the calibration on 1276, I showed Kurt the scrubber chemicals.  This was a mistake, since it exposed the sensor to outside air.  Starting the calibration, there was a 45+ppm offset in CO2 using Nitrogen.  Replaced the scrubber chemicals in both bottles, reinstalled, and waited overnight (the manual says to wait 24 hours, but I only had 15 hours).  Did the "real" calibration the next morning and saw much lower offsets and perhaps less drift as well.
  
  

H2O spans seem a bit large.  I'll send this to CSI for comment.