Dear manager
We have a CO2 and H20 Profiles system which is the newest version.When we test it we find several problem,and we don't know why it is ?
The first one is that if we don't power the pump ,and the LI-840 output the data CO2 of all the layer are about 450ppm
,but once power the pump ,the data become about 504ppm,but the 504ppm is the span value.why ?
The second one is that we use the CR1000KD to control the valves of zero and CO2 Span value ,but when we chose the 9 ,10,11 intake true ,and the CO2 is also about 504ppm when we true the zero intake ,the same to the span value intake.So
I guess if the CR1000KD control the valve success.Please help me,thanks.
Wish to your advice!
We use the LI-820 model (same device but doesn't measure water vapour) in a variety of our applications, connected to both CR10Xs and CR1000s. What we do is measure the mV output from the LI-820 and calculate the CO2 ppm inside the logger. It's a simple differential voltage measurement and you can connect the leads to any available differential port. To calculate the ppm values, you just need to know the cell length and the offset.
My initial thought is that your LI-840 is not calibrated correctly. If you knew the mV output from the IR then you would know how it is responding. If you are not pumping gas through the LI-840 then it is simply measuring the CO2 trapped in the cell. If it is pinning out at 504ppm, then your mV reading from the IR should be 5V (or 2.5V, depending on your configuration). You can pump any other gas other than CO2 through the IR (we use N2) and you can see if the IR outputs 0mV (or 0ppm). I'm not quite sure why your span range is 504ppm...the measurement range of the LI-840 is 0-3000ppm CO2.
Sorry I can't help you with your keypad issue. I don't completing under the issue you are experiencing. Can you elaborate?
FYI, we calibrate our LI-820s and LI-800s independent of the dataloggers, connected directly to a computer via RS232 using the LiCor software.
SJP
OK,Thank you very much!I have resolved this problem!