Inaccurate BLD5079 Humidity/WME readings

[UK developer]

Hi

I have purchased and outdoor probe with a GE Protimeter BLD5079 probe to measure the moisture level in building structures.  The GE Protimeter MMS2 with the BLD5079 measures the moisture in an industry recognised WME (Wood Moisture Equivalent) % which ranges from 0% (dry) to 100% (saturated).

The BLD5079 is a probe with two probes which are used to measure the level of conduction between the points and therefore the level of moisture (wetter = more conduction).

I connected the BLD5079 to the outdoor probe and followed the instructions.  All set up fine.  However I cannot get the probes to register higher than 24% humidity (WME) even in a saturated sponge.  If I connect the BLD5079 to my Protimeter it registers 100% in the sponge and correctly in all structures I try (verified with a second protimeter kit from another manufacturer).

I have tried to calibrate the BLD5079 at 98% (verified actual WME in sample used) but every time I save it reverts back to 24%.  I note back in 2014 that recalibration was not available for 13 bit sensors but "due to demand" was to be reinstated.

Is it possible to get the raw signal from the device so that I can apply the appropriate algorithm?

Help!  :o)

John

[Zhiheng Cao]

The industry standard WME% does not start from 0% as that will be very high resistance of over 100GOhm, no meter is capable of reading that. Normally, the WME starts from 6 or 7%. 

below is the equation we use to convert resistance (unit: MOhm) to WME% which is published in some academic papers:

(Math.Log10(Math.Log10(resistance) + 1) – 1.061) / (-0.039)

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[Zhiheng Cao]

See figure 3a from http://www.vtt.fi/inf/pdf/publications/2000/P420.pdf

On Wed, Dec 13, 2017 at 5:25 PM, Zhiheng Cao <zhihe...@gmail.com> wrote:

The industry standard WME% does not start from 0% as that will be very high resistance of over 100GOhm, no meter is capable of reading that. Normally, the WME starts from 6 or 7%. 

below is the equation we use to convert resistance (unit: MOhm) to WME% which is published in some academic papers:

(Math.Log10(Math.Log10(resistance) + 1) – 1.061) / (-0.039)

On Wed, Dec 13, 2017 at 12:15 PM, UK developer <banne...@gmail.com> wrote:

Hi

I have purchased and outdoor probe with a GE Protimeter BLD5079 probe to measure the moisture level in building structures.  The GE Protimeter MMS2 with the BLD5079 measures the moisture in an industry recognised WME (Wood Moisture Equivalent) % which ranges from 0% (dry) to 100% (saturated).

The BLD5079 is a probe with two probes which are used to measure the level of conduction between the points and therefore the level of moisture (wetter = more conduction).

I connected the BLD5079 to the outdoor probe and followed the instructions.  All set up fine.  However I cannot get the probes to register higher than 24% humidity (WME) even in a saturated sponge.  If I connect the BLD5079 to my Protimeter it registers 100% in the sponge and correctly in all structures I try (verified with a second protimeter kit from another manufacturer).

I have tried to calibrate the BLD5079 at 98% (verified actual WME in sample used) but every time I save it reverts back to 24%.  I note back in 2014 that recalibration was not available for 13 bit sensors but "due to demand" was to be reinstated.

Is it possible to get the raw signal from the device so that I can apply the appropriate algorithm?

Help!  :o)

John

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[Zhiheng Cao]

If you look at http://www.elcometer.com/images/stories/PDFs/InstructionBooks/7000_WME.pdf

you will see that WME% of 26% or above already represents 100% humidity and is therefore "relative" i.e. not useful for the purpose of Protimeter.  A 100% WME reading is simply a special case for the Protimeter to show that there is a short circuit across the probe. I bet that you cannot change the condition to make the Protimeter repeatably read 99%, 98%, 97%... etc.

If you are a professional building inspector you will know what I mean.  

[UK developer]

Hi

Thanks for the prompt reply.

You are correct below 6 or 7 my meter reads "Low" - that explains why.

Thanks for the references I will have a read through and work out how to cross reference the remote readings with Protimeter readings.

Many thanks

John

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