Z axis calibration idea

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Originally Posted by jstrack2

For example if the container was just 10 x 10 cm wide then 1 g (~1 cm^3 of the salt water) would add just .1 mm of height. If the container is wider then the accuracy will be even greater. That's like the caliper. The scale has to fit the size of the container which is a drawback since the scale will have to connect to the microcontroller. Work will have to be done to get each different scale size to communicate with the microcontroller properly.

Of course with the caliper it is limited in height (maybe 150 mm), but the other two dimensions could be unlimited in size.

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How about instead of just buying a scale, one could buy load sensors that are accurate to the gram, then you can stick any container on top of it.

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Originally Posted by jstrack2

Why would it not be accurate? Calipers have extremely good accuracy. I saw on ebay one for only 9 dollars that had 0.02mm accuracy. The one posted was cheaper and had 0.1mm accuracy. Resistors will not achieve that. Plus calipers are much more reliable than using resistance.

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How do you plan on attaching a caliper to the water level?

Also, resistance would be plenty reliable. You wouldn't be measuring the resistance of the water, but the resistance in the strip, which will change lengths based on the height of the water.

Are there actually mechanical components used in the calipers or does it merely measure a difference in capacitance over the length of the slide?

the mechanical components keep the etched capacitors in close proximity and allow the scales to be moved relative to each other using a small roller wheel

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Originally Posted by mike_biddell

the mechanical components keep the etched capacitors in close proximity and allow the scales to be moved relative to each other using a small roller wheel

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The challenge would be to build that into a float cheap, but I don't know how you're going to keep them really close without having too much friction on the side of the container

It will be very hard to get the strip resistance to give accurate readings. This is why the digital calipers use capacitance.

I think that the wheel will have to be removed of course (and a few other various pieces). The caliper hopefully will then slide easily. It will be outside of the container. A thin rod attached to the caliper and float will then drop into the liquid. When the float rises the rod will be pushed up and push the caliper slide part up too. At least this is how I imagine it. It may not work, but I think its is worth trying.

Since it will move very slowly I don't know that vibrations will be a problem (although I could be wrong!).

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Originally Posted by jstrack2

It will be very hard to get the strip resistance to give accurate readings. This is why the digital calipers use capacitance.

I think that the wheel will have to be removed of course (and a few other various pieces). The caliper hopefully will then slide easily. It will be outside of the container. A thin rod attached to the caliper and float will then drop into the liquid. When the float rises the rod will be pushed up and push the caliper slide part up too. At least this is how I imagine it. It may not work, but I think its is worth trying.

Since it will move very slowly I don't know that vibrations will be a problem (although I could be wrong!).

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I think you will have a problem with with making a float big enough that it could lift the caliper. Remember that with the float, it won't start to actually float until the water level is at least the height of the float itself.

Quote:

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Originally Posted by jstrack2

It will be very hard to get the strip resistance to give accurate readings. This is why the digital calipers use capacitance.

I think that the wheel will have to be removed of course (and a few other various pieces). The caliper hopefully will then slide easily. It will be outside of the container. A thin rod attached to the caliper and float will then drop into the liquid. When the float rises the rod will be pushed up and push the caliper slide part up too. At least this is how I imagine it. It may not work, but I think its is worth trying.

Since it will move very slowly I don't know that vibrations will be a problem (although I could be wrong!).

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Why use the float to move the slider? use the float to move the scale

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Originally Posted by EthanSpitz

I think you will have a problem with with making a float big enough that it could lift the caliper. Remember that with the float, it won't start to actually float until the water level is at least the height of the float itself.

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depends on what you use as a float, some materials float better than others with less displacement.

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Originally Posted by EthanSpitz

I think you will have a problem with with making a float big enough that it could lift the caliper. Remember that with the float, it won't start to actually float until the water level is at least the height of the float itself.

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The container will have to be pre-filled some, but this shouldn't be too much of an issue.

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Originally Posted by Aztecphoenix

Why use the float to move the slider? use the float to move the scale

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I was thinking the slider would weigh less, but I think either is okay. Also though the scale will have a wire coming out of it, so moving it may be a bit messy.

I'm not sure exactly how this would be done, but perhaps using adjustable leverage on the scale could be made where the accuracy and max weight can be varied. So if the filled container is heavy then adjust it so accuracy is say 10 times less but it can hold 10 times more weight. This may be very tricky though.