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Bad Easy Reader?

#1
I've recently purchased a RapidRH 4.0 Easy Reader and sensors. I'm starting a resinous flooring installation on a local school and I've installed six sensors into the concrete at 40% depth of the slab.

I took readings approximately 1 day, 3 days and now a few weeks after installing the sensors. They've all came back at 99%. It is known to all involved that the slab is fairly wet.

The contractor had the vct contractor perform some relative humidity tests in the same area that my tests are in. He is getting readings in the mid 80's.

I went back to the site today and took readings again. I put the easy reader in the sensor, pulled it out and it read 99%. I waited about 10 - 15 seconds and did it again in the same sensor. It jumped down to 96%, repeated and then I got a 95%.

Why would it be getting different readings over multiple successive readings? Could the easy reader be bad?

My understanding is that all you have to do is put the reader in the sensor, wait a few seconds until it registers and pull it out and then that is your reading. It shouldn't take multiple inserts to read.

Any info is appreciated.

Thanks,

Jeremy
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#2
Jeremy:

You have multiple questions/things I would like to comment on here. I will try to take them in order:

1)
Quote:I've recently purchased a RapidRH 4.0 Easy Reader and sensors.


THANK YOU for the purchase. Used appropriately, you will find it to be a very valuable tool.

2)
Quote:The contractor had the vct contractor perform some relative humidity tests in the same area that my tests are in. He is getting readings in the mid 80's.

The best thing I can do is put a link from our website to help you understand this. The ASTM standard will soon make more of the different manufacturer's products/readings more uniform. http://www.wagnermeters.com/pdf/Accuracy_of_the_Rapid_RH.pdf

3)
Quote:I went back to the site today and took readings again. I put the easy reader in the sensor, pulled it out and it read 99%. I waited about 10 - 15 seconds and did it again in the same sensor. It jumped down to 96%, repeated and then I got a 95%.

There is NO problem with your reader. YOU ALWAYS TAKE THE FIRST READING YOU GET. All things being equal, temp. and RH% are inversely related. In other words, when you increase temp you decrease RH%. When you insert the reader over and over, you can create a small amount of heat between the contacts on the reader and the sensor plate. This increase in temp will potentially artificially decrease the RH% reading.

Jason
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#3
I will echo Jason's statement. The reader itself can influence the probe by transferring thermal energy to the probe. So if you have the reader in a hot vehicle or a warm pants pocket, the reader could be between 85 and 100 degrees, while the probe is in the slab at around 68 degrees. Leaving the mass of the reader in contact with the probe can cause the temperature of the probe to rise a tiny amount which will affect the RH reading you see. Always use the first reading you get from the probe.

The same phenomenon can happen placing a cold reader in the sensor which would cause the RH to read a bit higher if left in for an extended amount of time.

As far as the other RH readings done by others, you would need to analyze how their testing was done. Were they using Wagner Rapid RH? Where they using re-useable probes? Were those probes checked for calibration? Were they allowed to acclimate? Were their holes drilled properly?

Bottom line: The Wagner Rapid RH is NIST certified and extremely accurate when installed correctly. If you need to defend your position please let us know. We have found many ways these other probes can give improper readings. Wink
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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#4
Thank you both for the response.

I had talked to Ed with Wagner Meters yesterday morning before either of you had posted. He confirmed what you both have told me.

I haven't had a chance to confirm if the other contractor is performing his RH tests properly. All signs point to no at this point though.

I will keep you informed.

Thank you,

Jeremy
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#5
Just so you know, when you talked to Ed did you catch his last name? Huh

It's Ed Wagner!!! How cool is that? The guy is fab! Heart
JD Grafton
Concrete Answers for Flooring Problems
[email protected]
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