Yesterday (Wednesday) afternoon something happened to my HMP50 temp/humidity sensor, you can see the transition clearly at http://www.wunderground.com/weatherstation/WXDailyHistory.asp?ID=IPINECAY2&day=6&year=2009&month=8&graphspan=week
I pulled the gill plates off the sensor this evening, and discovered a bunch of salt(?) encrustations on the sensor, and some pretty serious pitting of the sensor body.
Strangely enough, the CR10X thinks the temperature has returned to a more reasonable 74 degrees F, EVEN THOUGH THE SENSOR IS NOT CONNECTED!
I have a couple of questions, if anyone has some thoughts:
1) What happened to this sensor, is it just not suitable for a marine environment? I had an HMP45C up for something like 6 years without any problems, but this HMP50 didn't make a year. Is there any way to clean the sensor?
2) Why would the datalogger come up with a reasonable number without a sensor connected? It's measuring a 1000 ohm Platinum Resistance Thermometer (PRT) [OOPS! My mistake, it's a voltage output device, so the datalogger could be seing any random bias instead of the appropriate voltage.]
Thanks!
* Last updated by: wpns on 8/6/2009 @ 7:52 PM *
Howdy!
Different types of salts in a saturated solution can be used to calibrate these sensors. Salt build up on the cap of the sensor will definitely skew your measurements.
The HMP50-L has a chrome plated outer body that will corrode, or pit, but it won't effect the performance of the sensor. All the sensor circuitry inside the housing is potted with epoxy EXCEPT the components exposed at the head of the sensor. To clean the sensor cap power the sensor down and remove it from the gill radiation shield. Get a cup filled with clean distilled water. MUST BE DISTILLED. Some purified water still contains minerals. Carefully work as much of the encrustation off the cap of the sensor without tearing the Gortex membrane as possible. Soak the cap in the distilled water. Try not to use a brush! Gently swish it around to help the salts dissolve. You might have to repeat this process several times with clean water to get all the salt off. Let the cap air dry. Screw it back in place. While the sensor is out of the gill radiation shield clean the gill shield with some warm soapy water and rinse it thoroughly and let it air dry. Work all the contaminants off the shield.
I'm hoping you're not seeing salt build up on the RH chip, or the temperature chip, inside the sensor head. The platinum RTD temperature chip is the small brown ceramic looking chip with two silver leads that's soldered in place. The RH chip is plugged into gold plated sockets which should be nice and shiny and NOT green or blue with corrosion. If you see corrosion here you might have to replace the sensor.
I've seen this same problem with HMP45Cs in coastal environments and you have to go through the same cleaning process.
When everything is dry hook it all back up and give it a test drive. Good luck!