Strange effect!

[HTwoGo]

Strange effect!

Hi all,

in preparation for some research I have built a simple sell on an electronic balance able to resolve 0.01g, the power supply and balance are controlled and report to a Pc and I am able task the system to run a setup and log the results, the preliminary results have me scratching my head.

On energizing the system I see an apparent initial INCREASE in the weight, of about 0.75 grams, with the expected loss of weight as the task is run. The complete cell weighs some 850g. the running parameters are top volts max 5 volts, middle amps 5A max, bottom weight. The conductors are as flexible as I can get and are supported some 100mm from the cell, the balance does not move up and down when weighing and will correctly weigh a 1g mass with the wires connected. If it was electro magnetic I would expect the result to be instant, the cell is covered but not sealed.

Any ideas welcome ?!!!!! 

Htwogo

[RunningBare]

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[tinu]

Excellent setup, Htwogo!!!

And awesome results!
I?ll be very, very interested in following your experiments.

For the moment I just want to let you know that I?ll be scratching my head besides you?
I?ll be thinking on the subject but right now I?m in a big hurry.

Here is one dirty idea; you?ll probably have to check it if not dismissed already:
- magnetic interaction between the cell&wires and something in the electronic balance (or something existing bellow/around it), due to the magnetic field at 5A.

If you replace the cell with a simple resistor and run the experiment again, you should know if this is the case. If it?s not, it?s needless to say that the discussion and the associated excitement will follow. The effect seems very strange indeed.

Another kind request for you in order to figure out what is happening would be to repeat the experiment and to vary the current/voltage in a linear manner from 0-5-0V and to plot the results. It may not tell much but it may reveal something extra.

I?d be also interested in telling us more about your setup (balance and software), if possible. Is it custom made?
(At that resolution and with automatic acquisition, a lot of extremely exciting hypotheses can be verified, in a lot of areas!)

I very warmly welcome you aboard,
Tinu

[HTwoGo]

...the set up is as follows at the moment...
the power supply is a Agilent 6632B able to out put up 20V and 5A the big plus with this is one it is programmable over GPIB (think USB for instruments) and it capable of voltage and current control. The power is also monitored over sense lines so what you see is what you get hence the great resolution 0.0001V and .001A, the unit was calibrated last week so the data is good.
The balance is a Mettler BB2440 it?s as old as the hills but it still calibrates and I have all of the cables and documentation, and I already have written the drivers that I need, it also has a facility for weighting animals so it doesn?t mind the constantly changing weight too much. It is capable of 2400g with a delta range of 400g @ 0.01g sort of a high resolution area that can move up and down the weight scale, this unit is controlled read over RS232 serial.
The software is LabView www.ni.com, I have been using it on and off for 17 years, the page above does not represent much work, it would have taken me longer to figure out what I wanted to do and how.
I have a number of LM35 (temperature) sensors planed for the cell, and the cell is destined for a glass reaction flask, but one thing at a time, now where are my power resistors?

[HTwoGo]

The strange weight increase seems to be due to some influence from the power leads, perhaps heating of the polymer jacket. I draw this from the recovery after the power is removed and the reported weight is seen to recover. Also I removed the leads, zeroed the balance, ran a 100 second task at 6V @ 5A powered down and removed the leads, here I only saw a steady weight reported with no change with time.

The ramp up did however show little current flow until 2.5V, I will look at this when I get my new cell configured, and running on DI water. This would suggest that the cell is not a dead resistance but has some threshold potential that must be over come before current can flow.

Best HTowGo