Do moon phases affect weighing precision on the microgram range?

In summary: The mass will apparently lose up to ~0.015 g after achieving the temperature set point, and this drift will continue for several hours. This is caused by convection currents, which are driven by the temperature of the sample. If you hold the sample at the set temperature for a few hours, the drift will stop.
  • #1
lionpauu
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TL;DR Summary
Do Moon phases affect weighing precision on the microgram range, over several hours days at elevated temperatures?
Hi,

I'm looking to improve the precision of a system over a several hour cycle of operation of +50°C operation.
The mass is ~11g and is suspended below the balance via a factory provided point. The "sample" is enclosed within a large borosilicate flask 150mm dia x 450 mm height that is trace heated the floor is also heated and all report a 0.1°C deviation from the setpoint of 50°C. The sample itself is monitored via a non-contact IR sensor and reports a 0.1g °C max variation.

So the problem is that the sample will apparently lose up to ~0.015 g after achieving the temperature set point, and this drift will continue for several hours. I have reduced this rate by better sealing the falsk to air ingress and also I think some of the system was accumulating a static charge.

So my question is has anyone an explication of why the loss and recovery inverse to temperature, the loss in air density should increase the apparent wt, could the lunar cycle be having an impact? My balance can resolve 0.0001g and I am logging the data remotely.

There is more on my problem on twitter...

 
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  • #2
Tidal accelerations are of the order of ## \frac{m_M GR_{E}}{d^3} = 5\cdot10^{-7} \frac{m}{s^2}##, for an 11 gram object that's ~5 nanonewton or the weight of ~0.5 microgram. Whatever you see, it's not coming from the Moon.

A static charge could produce a force like that.
 
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  • #3
Welcome to PF.

Convection currents, driven by the temperature of the sample, could cause problems by dragging the sample upwards.

If you think the effect is tidal, then set up a reference weight and record the reading over the next 24 hours. Does the data show two cycles of tide per day ?
 
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  • #4
Even if it's coming from the moon, it's not coming from the phase of the moon, which is a statement about from which direction the moon is lit.
 
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  • #5
Vanadium 50 said:
Even if it's coming from the moon, it's not coming from the phase of the moon, which is a statement about from which direction the moon is lit.
True, but the tidal range is significantly greater during the new or full moon. Then the Sun, Earth and Moon lie on a straight line.
 
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  • #6
mfb said:
A static charge could produce a force like that.
Should be easy enough to set up an ionizer to eliminate that variable. Probably the quickest way.
 
  • #7
Some thoughts:
Does your instrumentation drift? Check for zero shift with zero weight, both with and without heat.
Is there a chemical reaction that releases a small amount of material as a gas? Repeat test with a metal sample.
Is something evaporating? Ditto.
Is the effect temperature dependent? Check by testing at, for example, 30 and 40 deg C.
Are convective air currents pulling the warm object up?
What happens if you hold at 50 deg C for several hours, then shut the heater off while continuing logging until it cools to room temperature?
What happens if you hold at temperature for 24 (or more) hours?

You cannot assume that instrumentation is measuring what you think it is measuring. You need to check everything before running an actual test. I used to call it "testing the test".
 
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