VR3 O2 cell calibration

EBT

Could be a capacitance change. I've had databusses before where the insulation had been "pinched". The cable passes continuity test fine, but if you try and pass a high speed datastream down it, the capacitance change rounds off the pulses.

I've seen this on a few different things, from RS422 buses, SCADA buses to UTP ethernet.

Not saying that this is the case, just pointing out that they have a point about communications being more than just continuity.

Take a good look at your cable, has it been kinked or pinched?

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mortenkjerulff

Thanks everyone.

The idea with a bad cable and/or corrosion gives me new hope.
I will check it and report back in a day or two.

By the way, I do the calibration outside the loop as I think this gives the most accurate result.

Morten

steevke

You could always put a millivolt signal instead of a cell to check everything.

You can easily create one with a small AA battery, a resistor and a (multi-turn) trimpot. You need a voltage divider - if you don't know how to build one give a yell and I'll draw up schematic. You also need a multi-meter to check voltages.

First: create a 10mV signal (usually cells put out +- 10 mV when new in air).
Apply to VR3 -> calibrate for air. Remove input, create 47.5mV signal, apply to VR3. This should give you +- 100%.

Use your cable when applying these signals. Putting voltages directly on the pins will be difficult to say the least.

And don't shoot ME if YOU f**k your VR3 up when doing this test...

Steven

mortenkjerulff

Well... As promised.

I tried different things today:

The cable seems to be fine (tried it elsewhere and the cell on it showd 21% in air and 99% in oxygen).

Notised some corrosion in the fisher connector on the VR3, down in one the female connectors, which I tried to remove. This actually helped a little, so I guess this is the way to go. Not easy though...

Must clean connector more...

Thanks for your help everyone.

Morten

Mdemon

I soak mine in citric acid every now and then - an easy way to keep contacts clean. I do the same with my Suunto Vyper as an invisible buildup between contacts can stop it going into powersave mode and eats the battery.

HTH

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darthmuhl

I had a similar problem with a VR2 and know of a problem with a VR3. My VR2 gave consistently high fO2 readings (+2-3%) when plugged into my Azimuth SCR. I tested against a VR3 that the problem was with the VR2 and not the cable or csensor.
I sent it back to Azimuth and after ten weeks they confirmed that the problem was with the VR2 and they sent me a new computer which works fine.
The guy with the VR3 sent it back and forth one or more times but never confirmed that the problem was solved and now compensates by adjusting the conservatism factor.

I remain puzzled why a computer could have software problems like this.

Carl

mortenkjerulff

After much more cleaning of the fisher connecter(s) my VR3 finally works perfect again

The next time I have problems like this, I think the "cook book" to solve the problem will be something like:


1) Unplug the cable and check what the VR3 is reading. If it is reading something (in my case some garbled numbers, much like numbers from the Klingon language ) it is the connector on the VR3 that has some corrosion on it.

2) Insert the cable without the sensor on plugged in. If the VR3 is now reading something again (f.ex. Klingon numbers or just normal numbers), the cable is probably corroded somewhere. It is probably between the small pins, but also check where the wires are soldered, as in my case water had actually had access to the back of the connector and made lots of corrosion that actually generated a little voltage by itself.

As Mdemon suggests I will check and clean my connectors more often from now on

Morten