| Author | Message | |||
     Johan Gravett (johan_gravett) New member Username: johan_gravett Post Number: 3 Registered: 4-2010 |
Thank you Tony and Pierre. I have indeed registered for the NIR2011 conference and will see you in Cape Town. Regarding the ICNIRS, I am holding back a while until after the conference, then will make a final descision. Regards. | |||
| Pierre Dardenne (dardenne) Senior Member Username: dardenne Post Number: 59 Registered: 3-2002 |
Dear Tony, Thanks to promote NIR2011! Johan, indeed do register to http://www.icnirs.org/ too! Pierre | |||
| Tony Davies (td) Moderator Username: td Post Number: 254 Registered: 1-2001 |
Hi again Johan, I promised to post the references which are: A.M.C. Davies and A. Grant, Appl. Spectrosc., 41,1248 (1987). A.M.C. Davies, NIR news, 3(1), 8 (1992). K.H. Norris, NIR news, 3(3), 4 (1992). Our experience was that we moved the spectrometer so that it was as far as possible from the in-coming air. It might be helpful to install a ceiling fan to try to mix the air before it arrives at the spectrometer. Is it important? My original suggestion (like Dave's) was that it was a nuisance but probably not likely to cause calibration problems but Karl Norris disagreed. On another topic: Do you know that the International NIR Conference will be held in Capetown in May? You really should go to it and become a member of the international family. Not to be missed; I hope you are already registered! Best wishes, Tony | |||
| Johan Gravett (johan_gravett) New member Username: johan_gravett Post Number: 2 Registered: 4-2010 |
Thank you to everyone who replied and supplied the answers. Yes, we are new to the NIR as I was introduced recently into this fascinating world. Our instrument is in a small room but share a common air conditioner with the rest of the building. We are in Durban, South Africa and the humidity here is very high. I think this is were the moisture is coming from. We will try to seal this room more efficiently. | |||
| Jose Miguel Hernandez Hierro (jmhhierro) Intermediate Member Username: jmhhierro Post Number: 16 Registered: 4-2008 |
Hello Johan, I use the same instrument, this is water noise. I also recomend you to check the fan filter Best regards | |||
| David W. Hopkins (dhopkins) Senior Member Username: dhopkins Post Number: 188 Registered: 10-2002 |
Hi Johan, I have used a similar instrument for many years -- with great success. I have found that this problem is frequently observed if you run the noise test just after turning on the lamp. I would recommend that the instrument be allowed to warm up for at least 30 min, and I usually used 60 min for best results. Such differences generally disappear after even 15 minutes, in my small laboratory. By the way, to preserve the lamp life, I have found it best to turn off the lamp at the end of a work day, and turn it on an hour before I want to use the instrument. That seems to help the water vapor to equilibrate within the instrument. It is changes in the water vapor content over the times of the scans that cause the noise peaks. The presence of a nearly constant amount of water vapor is not detected by the noise test, and will ordinarily be no problem in the use of the instrument. Are these differences significant? I doubt it. You can judge from the magnitude of the changes in comparison to the magnitude of the B-coefficients for your applications, the changes are probably negligible. A more sensitive test would be to add these noise scans to a few representative samples, and see by how much the predictions change. Best regards, Dave | |||
| Tony Davies (td) Moderator Username: td Post Number: 253 Registered: 1-2001 |
Hi Johan, Welcome to the group. This is water vapour noise (WVN). We reported this around 1984 in our Neotec 6350 spectrometer at FRI, Norwich, UK. It is caused by variation in the atmospheric water vapour while the measurement of the reference and sample are made. In our case it was caused by placing the spectrometer in a small lab with a local air conditioning system. How can the spectrometer detect such a small change? You have up to a meter of pathlength inside the spectrometer and you are measuring against a noise background of around 30 x 10^5. The problem is very serious in mid-IR spectrometers so that they use a nitrogen purge to keep water vapour out of the spectrometer. What can you do about it? It depends what is causing your WVN. It may (like ours) be related to air-conditioning or it may be due to your local weather; where are you located? Ideally you should locate your spectrometer in a large air-conditioned laboratory which does not get direct sunlight. Is it important? Yes, after we reported it, Karl Norris devised an experiment which detected various amounts of WVN in a set of wheat spectra. It is very difficult to be sure how much this affects results but it is undesirable. I will find some references and post them later. Best wishes, Tony | |||
| Jos� Ram�n Cuesta (jrcuesta) Junior Member Username: jrcuesta Post Number: 10 Registered: 11-2009 |
Problems with Moisture. | |||
| Johan Gravett (johan_gravett) New member Username: johan_gravett Post Number: 1 Registered: 4-2010 |
Hi, we are getting interferences at some of our sites and when the performance test does not pass, the noise spectra looks like the one in the attached documnet. There are peaks and valleys in the range 1300 to 1450 and again at 1800 to 1900. The instrument is a FOSS 5000 with IsiScan. Can anyone tell where to start looking, because this is intermittet and does not appear every day. I think it might be some electrical interference from another instrument in the room or building. I will try to attach a screen image of the problem.
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Noise Spectra